What is claimed is:1. A hammer assembly for use in a pneumatic gun, said pneumatic gun for firing projectiles by use of compressed gas as a propellant, said pneumatic gun comprising:(1) a recock chamber, and(2) a valve, said valve normally closed and impact openable, said valve comprising a valve seat;said hammer assembly comprising:(a) an impacter, said impacter slidably translatable within said recock chamber between a cocked position and a valve-opening position, said valve-opening position closer than said cocked position to said valve seat, said impacter biased toward said valve-opening position, said impacter comprising:(i) an impacter body portion;(ii) an impact imparting face, said valve receptive to an impact by said impact imparting face when said impacter moves to said valve-opening position, so that momentum is provided to said valve by said impacter to open said valve; and(iii) an impacter contact face;(b) a recock piston, said recock piston slidably translatable within said recock chamber between a piston ready-to-fire position and an impacter-cocking position, said piston ready-to-fire position closer than said impacter-cocking position to said valve seat, said recock piston directly or indirectly biased toward said piston ready-to-fire position, said recock piston comprising:(i) a pressure receiving face, said pressure receiving face slidable within said recock chamber; and(ii) a longitudinal passageway, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal;said transfer portal disposed between said impacter body portion and said valve seat, so that the momentum provided by said impacter to open said valve passes through said transfer portal;said impacter contact face directly or indirectly engageable by said recock piston,wherein as said recock piston moves from said piston ready-to-fire position to said impacter-cocking position, said impacter moves from said valve opening position to said cocked position, andwherein said recock piston returns to said piston ready-to-fire position independently of said impacter;whereby said impacter and said recock piston separately provide a valve opening function and a recock function, respectively, for said pneumatic gun.2. A hammer assembly for use in a pneumatic gun, said pneumatic gun for firing projectiles by use of compressed gas as a propellant, said pneumatic gun comprising:(1) a first end and a second end;(2) a user actuable trigger(3) a gas reservoir, said gas reservoir for containing compressed gas therein;(4) a valve, said valve normally closed and impact openable for releasing, when open, compressed gas from said gas reservoir, said valve comprising an impact receiving face;(5) a recock chamber, said recock chamber comprising a sealable portion, said sealable portion in fluid communication with said valve so that when said valve is open a portion of the compressed gas released flows into said sealable portion,(6) an impacter sear, said impacter sear controlled by said user-actuable trigger;said hammer assembly comprising:(a) an impacter, said impacter slidably translatable within said recock chamber between a cocked position and a valve-opening position, said valve-opening position closer than said cocked position to said first end of said gun, said impacter biased toward said valve-opening position, said impacter comprising:(i) an impact imparting face, said impact imparting face acting on said impact receiving face when said impacter moves to said valve-opening position, so that momentum is provided to said valve by said impacter to open said valve;(ii) an impacter contact face; and(iii) a sear shoulder, said sear shoulder engageable by said impacter sear when said impacter is in said cocked position, so that said impacter is restrained in said cocked position until said impacter is released in response to actuation of said user-actuable trigger;(b) a recock piston, said recock piston slidably translatable within said recock chamber between a piston ready-to-fire position and an impacter-cocking position, said piston ready-to-fire position closer than said impacter-cocking position to said first end of said gun, said recock piston directly or indirectly biased toward said piston ready-to-fire position, said recock piston comprising a pressure receiving face, said pressure receiving face slidable within said sealable portion of said recock chamber, said pressure receiving face responsive to the urging of the portion of compressed gas released into said sealable portion of said recock chamber to move said recock piston from said piston ready-to-fire position to said impacter-cocking position;said impacter contact face directly or indirectly engageable by said recock piston,wherein as said recock piston moves from said piston ready-to-fire position to said impacter-cocking position, said impacter moves from said valve-opening position to said cocked position, andwherein said recock piston returns to said piston ready-to-fire position while said impacter is restrained in said cocked position by said impacter sear,whereby said impacter and said recock piston separately provide a valve opening function and a recock function, respectively, for said pneumatic gun.3. A hammer assembly for use in a pneumatic gun, said pneumatic gun for firing projectiles by use of compressed gas as a propellant, said pneumatic gun comprising:(1) a user-actuable trigger(2) a gas reservoir, said gas reservoir for containing compressed gas therein;(3) a valve, said valve normally closed and impact openable for releasing, when open, compressed gas from said gas reservoir, said valve comprising an impact receiving face and a valve seat;(4) a recock chamber, said recock chamber comprising a sealable portion, said sealable portion being in fluid communication with said valve so that when said valve is open a portion of the compressed gas released flows into said sealable portion;(5) an impacter sear, said impacter sear controlled by said user-actuable trigger;said hammer assembly comprising:(a) an impacter, said impacter slidably translatable within said recock chamber between a cocked position and a valve-opening position, said valve-opening position closer than said cocked position to said valve seat, said impacter biased toward said valve-opening position, said impacter comprising:(i) an impacter body portion;(ii) an impact imparting face, said impact imparting face acting on said impact receiving face when said impacter moves to said valve-opening position, so that momentum is provided to said valve by said impacter to open said valve;(iii) an impacter contact face; and(iv) a sear shoulder, said sear shoulder engageable by said impacter sear when said impacter is in said cocked position, so that said impacter is restrained in said cocked position until said impacter is released in response to actuation of said user-actuable trigger;(b) a recock piston, said recock piston slidably translatable within said recock chamber between a piston ready-to-fire position and an impacter-cocking position, said piston ready-to-fire position closer than said impacter-cocking position to said valve seat, said recock piston directly or indirectly biased toward said piston ready-to-fire position, said recock piston comprising:(i) a pressure receiving face, said pressure receiving face oriented toward said valve seat and slidable within said sealable portion of said recock chamber, said pressure receiving face responsive to the urging of the portion of compressed gas released into said sealable portion of said recock chamber to move said recock piston from said piston ready-to-fire position to said impacter-cocking position;(ii) a longitudinal passageway, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal, said transfer portal disposed between said impacter body portion and said valve seat, so that the momentum provided by said impacter to said valve to open said valve passes through said transfer portal;said impacter contact face directly or indirectly engageable by said recock piston, so that as said recock piston moves from said piston ready-to-fire position to said impacter-cocking position, said impacter moves from said valve-opening position to said cocked position, and so that said recock piston returns to said piston ready-to-fire position while said impacter remains restrained in said cocked position by said impacter sear;whereby said impacter and said recock piston separately provide a valve opening function and a recock function, respectively, for said pneumatic gun.4. A hammer assembly for use in a pneumatic gun, said pneumatic gun for firing projectiles by use of compressed gas as a propellant, said pneumatic gun comprising:(1) a user actuable trigger;(2) a forward end and a rearward end;(3) a gas reservoir, said gas reservoir for containing compressed gas therein;(4) a valve, said valve normally closed and impact openable to release compressed gas from said gas reservoir, said valve comprising a rearwardly directed impact receiving face;(5) a recock chamber, said recock chamber comprising forwardly a sealable portion, said sealable portion in fluid communication with said valve so that when said valve is open a portion of the compressed gas released flows into said sealable portion,(6) an impacter sear, said impacter sear controlled by said user-actuable trigger;said hammer assembly comprising:(a) an impacter, said impacter slidably translatable within said recock chamber between a cocked position and a valve-opening position, said impacter forwardly biased toward said valve-opening position, said impacter comprising:(i) an impacter body portion;(ii) an impact imparting face, said impact imparting face forwardly directed, said impact imparting face acting on said impact receiving face when said impacter moves to said valve-opening position, so that momentum is provided by said impacter to open said valve;(iii) a forwardly-directed impacter contact face; and(iv) a forwardly-directed sear shoulder, said sear shoulder engageable on said impacter sear when said impacter is in said cocked position, so that said impacter is restrained in said cocked position until said impacter is released in response to actuation of said user actuable trigger;(b) a recock piston, said recock piston slidably translatable within said recock chamber between a piston ready-to-fire position and an impacter-cocking position, said recock piston directly or indirectly biased forward toward said piston ready-to-fire position, said recock piston comprising a forwardly-directed pressure receiving face slidable within said sealable portion of said recock chamber, said pressure receiving face responsive to the urging of the portion of compressed gas released into said sealable portion of said recock chamber to move said recock piston from said piston ready-to-fire position to said impacter-cocking position;said impacter body portion located rearward of said pressure receiving face of said recock piston;said impacter contact face directly or indirectly engageable by said recock piston,wherein as said recock piston moves from said piston ready-to-fire position to said impacter-cocking position, said impacter moves from said valve-opening position to said cocked position, andwherein said recock piston returns to said piston ready-to-fire position while said impacter is restrained in said cocked position by said impacter sear;whereby said impacter and said recock piston separately provide a valve opening function and a recock function, respectively, for said pneumatic gun.5. A hammer assembly for use in a pneumatic gun, said pneumatic gun for firing projectiles by use of compressed gas as a propellant, said pneumatic gun comprising:(1) a user actuable trigger;(2) a forward end and a rearward end;(3) a gas reservoir, said gas reservoir for containing compressed gas therein;(4) a valve, said valve normally closed and impact openable to release compressed gas from said gas reservoir, said valve comprising a rearwardly directed impact receiving face;(5) a recock chamber, said recock chamber comprising forwardly a sealable portion, said sealable portion in fluid communication with said valve so that when said valve is open a portion of the compressed gas released flows into said sealable portion,(6) an impacter sear, said impacter sear controlled by said user-actuable trigger;said hammer assembly comprising:(a) an impacter, said impacter slidably translatable within said recock chamber between a cocked position and a valve-opening position, said impacter forwardly biased toward said valve-opening position, said impacter comprising:(i) an impacter body portion;(ii) an impact imparting face, said impact imparting face forwardly directed, said impact imparting face acting on said impact receiving face when said impacter moves to said valve-opening position, so that momentum is provided by said impacter to open said valve;(iii) a forwardly-directed impacter contact face; and(iv) a forwardly-directed sear shoulder, said sear shoulder engageable on said impacter sear when said impacter is in said cocked position, so that said impacter is restrained in said cocked position until said impacter is released in response to actuation of said user-actuable trigger;(b) a recock piston, said recock piston slidably translatable within said recock chamber between a piston ready-to-fire position and an impacter-cocking position, said recock piston directly or indirectly biased forward toward said piston ready-to-fire position, said recock piston comprising:(i) a forwardly-directed pressure receiving face, said pressure receiving face slidable within said sealable portion of said recock chamber, said pressure receiving face responsive to the urging of the portion of compressed gas released into said sealable portion of said recock chamber to move said recock piston from said piston ready-to-fire position to said impacter-cocking position: and(ii) a longitudinal passageway, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal;said transfer portal located forward of said impacter body portion, so that the momentum provided by said impacter to open said valve passes through said transfer portal;said impacter contact face directly or indirectly engageable by said recock piston,wherein as said recock piston moves from said piston ready-to-fire position to said impacter-cocking position, said impacter moves from said valve-opening position to said cocked position, andwherein said recock piston returns to said piston ready-to-fire position while said impacter is restrained in said cocked position by said impacter sear;whereby said impacter and said recock piston separately provide a valve opening function and a recock function, respectively, for said pneumatic gun.6. The pneumatic gun as set forth in claim 5, further comprising:(a) a bolt chamber;(b) a loading port, said loading port when open accommodating the passage of a new projectile into said bolt chamber(c) a bolt, said bolt slidably translatable within said bolt chamber between:(i) a bolt open position, said loading port open when said bolt is in said bolt open position, and(ii) a bolt ready-to-fire position, said bolt closing said loading port when in said bolt ready-to-fire position, said bolt chambering said new projectile as said bolt moves from said bolt open position to said bolt ready-to-fire position;said bolt directly or indirectly biased forward toward said bolt ready-to-fire position;(d) a connecting rod, said connecting rod constraining said bolt and said recock piston to translate in concert.7. The pneumatic gun as set forth in claim 5, further comprising:(a) a bolt chamber;(b) a loading port, said loading port when open accommodating the passage of a projectile into said bolt chamber;(c) a bolt, said bolt slidably translatable within said bolt chamber between:(i) a bolt open position, said loading port open when said bolt is in said bolt open position, and(ii) a bolt ready-to-fire position, said bolt closing said loading port when in said bolt ready-to-fire position, said bolt chambering said new projectile as said bolt moves from said bolt open position to said bolt ready-to-fire position;said bolt directly or indirectly biased forward toward said bolt ready-to-fire position;(d) a bolt connection bar, said bolt connection bar comprising a forwardly-directed bolt contact face, said bolt contact face engageable with said recock piston so that (A) when said recock piston travels rearward to said impacter-cocking position said bolt is pushed rearward to said bolt open position, and (B) when said bolt travels forward to said bolt ready-to-fire position, said recock piston is pushed forward to said piston ready-to-fire position.8. The apparatus as set forth in claim 5, wherein said valve further comprises a valve seat and a valve ball, said valve ball comprising a first surface providing said impact receiving face and a second surface providing a valve seal, said valve ball sealingly engageable on said valve seat, said valve ball displaceable from said valve seat in response to impact to open said valve.9. The apparatus as set forth in claim 5, wherein said valve further comprises a valve pin, said valve pin comprising said impact receiving face.10. The apparatus as set forth in claim 9, wherein said valve pin fits in sliding engagement within and effectively seals said transfer portal against the passage of compressed gas during at least a portion of the rearward travel of said recock piston from said piston ready-to-fire position to said impacter-cocking position.11. The apparatus as set forth in claim 5, said impacter further comprises an elongated nose portion, said elongated nose portion comprising said impact imparting face, said elongated nose portion sized to fit slidably within said longitudinal passageway.12. The apparatus as set forth in claim 11, wherein said elongated nose portion is sized to substantially seal said longitudinal passageway, so that during recocking of said gun said elongated nose portion effectively prevents the escape of compressed gas through said longitudinal passageway during a portion of the rearward movement of said recock piston from said piston ready-to-fire position to said impacter-cocking position.13. The apparatus as set forth in claim 12, wherein said elongated nose portion is sufficiently short that when said impacter is in said cocked position, said longitudinal passageway is open during a portion the forward movement of said recock piston from said impacter-cocking position to said piston ready-to-fire position, so that compressed gas in said sealed portion of said recock chamber can escape through said longitudinal passageway and said transfer portal.14. The apparatus as set forth in clam 12, wherein said elongated nose portion further comprises a flat extending longitudinally on said elongated nose portion so when said impacter is in said cocked position, said longitudinal passageway is open to the flow of compressed gas from said recock chamber during a portion the forward displacement of said recock piston from said impacter-cocking position to said piston ready-to-fire position, so that compressed gas in said sealed portion of said recock chamber can escape through said longitudinal passageway and said transfer portal.15. The apparatus as set forth in claim 5, wherein said recock piston further comprises a transfer pin, said transfer pin situated interposed between said impact imparting face and said impact receiving face, said transfer pin transferring momentum of said impacter to said valve to open said valve, said transfer pin sized and shaped for close fitting engagement with, and slidingly translatable movement within, said transfer portal.16. The apparatus as set forth in claim 5, wherein said transfer portal is slidably receptive therethrough of one or more members selected from the group consisting of (A) an elongated nose portion of said impacter, said elongated nose portion comprising said impact imparting face, (B) a valve pin portion of said valve, said valve pin portion comprising said impact receiving face, and (C) a transfer pin, said transfer pin comprising (i) a transfer pin impact receiving face engageable on said impact imparting face of said impacter, and (ii) a transfer pin impact imparting face engageable on said impact receiving face of said valve.17. The apparatus as set forth in claim 5, said impacter body portion further comprises a middle portion, and wherein said recock piston further comprises a cavity, said cavity defined by interior sidewalls, said cavity sized and shaped so that said middle portion is slidable at least partially within said cavity.18. The apparatus as set forth in claim 17, wherein said recock piston further comprises a registration slot, and wherein said impacter further comprises a registration boss, said registration boss traveling slidingly rearward and forward through said registration slot and substantially preventing said impacter from rolling on its longitudinal axis.19. The apparatus as set forth in claim 18, wherein said registration boss is detachably affixable to said impacter.20. The apparatus as set forth in claim 18, wherein said registration boss further comprises said impacter sear shoulder.21. The apparatus as set forth in claim 5, said recock piston further comprises a recock piston bore defined by interior sidewalls, and wherein said impacter body portion fits slidably within said recock piston bore.22. The apparatus as set forth in claim 5, wherein said impacter body portion further comprises a middle portion, and wherein said recock piston further comprises a generally horizontally U-shaped structure having an interior sidewall, said structure having a primary open end oriented rearward, said U-shaped structure sized and shaped so that said middle portion is slidable at least partially within said structure.23. The apparatus as set forth in claim 5, wherein said gun further comprises a piston sear, and wherein said recock piston further comprises a piston sear engagement shoulder engageable on said piston sear to selectively restrain said recock piston in said impacter-cocking position.24. A hammer assembly for use in a pneumatic gun, said pneumatic gun for firing projectiles by use of compressed gas as a propellant, said pneumatic gun comprising:(1) a user actuable trigger,(2) a forward end and a rearward end;(3) a gas reservoir, said gas reservoir for containing compressed gas therein;(4) a valve, said valve normally closed and impact openable to release compressed gas from said gas reservoir, said valve comprising a rearwardly directed impact receiving face;(5) a recock chamber, said recock chamber comprising forwardly a sealable portion, said sealable portion in fluid communication with said valve so that when said valve is open a portion of the compressed gas released flows into said sealable portion,(6) an impacter sear, said impacter sear controlled by said user-actuable trigger;(7) a bolt chamber,(8) a loading port;(9) a bolt, said bolt slidably translatable within said bolt chamber between:(i) a bolt ready-to-fire position, said bolt when in said bolt ready-to-fire position closing said loading port, and(ii) a bolt open position, said bolt when in said bolt open position opening said loading port to accommodate the passage of a projectile into said bolt chamber forward of said bolt,said bolt directly or indirectly biased forward toward said bolt ready-to-fire position;said hammer assembly comprising:(a) an impacter, said impacter slidably translatable within said recock chamber between a cocked position and a valve-opening position, said impacter forwardly biased toward said valve-opening position, said impacter comprising:(i) an impacter body portion;(ii) an impact imparting face, said impact imparting face forwardly directed, said impact imparting face acting on said impact receiving face when said impacter moves to said valve-opening position, so that momentum is provided by said impacter to open said valve;(iii) a forwardly-directed impacter contact face; and(iv) a forwardly-directed sear shoulder, said sear shoulder engageable on said impacter sear when said impacter is in said cocked position, so that said impacter is restrained in said cocked position until said impacter is released in response to actuation of said user-actuable trigger;(b) a recock piston, said recock piston slidably translatable within said recock chamber between a piston ready-to-fire position and an impacter-cocking position, said recock piston directly or indirectly biased forward toward said piston ready-to-fire position, said recock piston comprising:(i) a forwardly-directed pressure receiving face, said pressure receiving face slidable within said sealable portion of said recock chamber, said pressure receiving face responsive to the urging of the portion of compressed gas released into said sealable portion of said recock chamber to move said recock piston from said piston ready-to-fire position to said impacter-cocking position; and(ii) a longitudinal passageway, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal;said transfer portal located forward of said impacter body portion, so that the momentum provided by said impacter to open said valve passes through said transfer portal;said impacter contact face directly or indirectly engageable by said recock piston,wherein as said recock piston moves from said piston ready-to-fire position to said impacter-cocking position, said impacter moves from said valve-opening position to said cocked position, andwherein said recock piston returns to said piston ready-to-fire position while said impacter is restrained in said cocked position by said impacter sear;said bolt constrained to travel rearward when said recock piston travels rearward, and said recock piston constrained to travel forward when said bolt travels forward, so that when said recock piston moves rearward to said impacter-cocking position said bolt moves rearward to said bolt open position, and so that when said bolt moves forward to said bolt ready-to-fire position said recock piston moves forward to said piston ready-to-fire position;whereby said impacter and said recock piston separately provide a valve opening function and a recock function, respectively, for said pneumatic gun.25. The apparatus as set forth in claim 24, said bolt further comprising a rearwardly-directed bolt contact face, said bolt contact face engageable with said impacter so that as said recock piston moves rearward, said recock piston directly engages said bolt to move said bolt rearward, and said recock piston indirectly engages said impacter to move said impacter rearward.26. The apparatus as set forth in claim 24, said gun further comprises a bolt spring, said bolt spring directly biasing said bolt forward, said bolt spring indirectly biasing said recock piston forward.27. The apparatus as set forth in claim 24, said gun further comprises a frame, said frame comprising a single longitudinal cavity, said single longitudinal cavity comprising said recock chamber, and said bolt chamber.28. The apparatus as set forth in claim 27, wherein said gun further comprises a connecting rod, said connecting rod comprising an elongated generally U-shaped link-like member having an extended body portion and relatively short first end and second end members, said first and said second end members fitting within corresponding first and second connecting rod recesses in said bolt and said recock piston, respectively, said connecting rod constraining said bolt and said recock piston to translate in concert.29. The apparatus as set forth in claim 24, wherein said gun further comprises a frame, said frame comprising a first longitudinal cavity, said first longitudinal cavity comprising said bolt chamber, said frame further comprising a second longitudinal cavity, said second longitudinal cavity comprising said recock chamber.30. A hammer assembly for use in a pneumatic gun, said pneumatic gun for firing projectiles by use of compressed gas as a propellant, said pneumatic gun comprising:(1) a user actuable trigger;(2) a forward end and a rearward end;(3) a gas reservoir, said gas reservoir for containing compressed gas therein;(4) a valve, said valve normally closed and impact openable to release compressed gas from said gas reservoir, said valve comprising a rearwardly directed impact receiving face;(5) a recock chamber, said recock chamber comprising forwardly a sealable portion, said sealable portion in fluid communication with said valve so that when said valve is open a portion of the compressed gas released flows into said sealable portion,(6) an impacter sear, said impacter sear controlled by said user-actuable trigger;(7) a bolt chamber(8) a loading port;(9) a bolt, said bolt slidably translatable within said bolt chamber between:(i) a bolt ready-to-fire position, said bolt when in said bolt ready-to-fire position closing said loading port, and(ii) a bolt open position, said bolt when in said bolt open position opening said loading port to accommodate the passage of a projectile into said bolt chamber forward of said bolt,said bolt directly or indirectly biased forward toward said bolt ready-to-fire position;said hammer assembly comprising:(a) an impacter, said impacter slidably translatable within said recock, chamber between a cocked position and a valve-opening position, said impacter forwardly biased toward said valve-opening position, said impacter comprising:(i) an impacter body portion;(ii) an impact imparting face, said impact imparting face forwardly directed, said impact imparting face acting on said impact receiving face when said impacter moves to said valve-opening position, so that momentum is provided by said impacter to open said valve;(iii) a forwardly-directed impacter contact face; and(iv) a forwardly-directed sear shoulder, said sear shoulder engageable on said impacter sear when said impacter is in said cocked position, so that said impacter is restrained in said cocked position until said impacter is released in response to actuation of said user-actuable trigger;(b) a recock piston, said recock piston slidably translatable within said recock chamber between a piston ready-to-fire position and an impacter-cocking position, said recock piston directly or indirectly biased forward toward said piston ready-to-fire position, said recock piston comprising:(i) a forwardly-directed pressure receiving face, said pressure receiving face slidable within said sealable portion of said recock chamber, said pressure receiving face responsive to the urging of the portion of compressed gas released into said sealable portion of said recock chamber to move said recock piston from said piston ready-to-fire position to said impacter-cocking position; and(ii) a longitudinal passageway, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal;said transfer portal located forward of said impacter body portion, so that the momentum provided by said impacter to open said valve passes through said transfer portal;said impacter contact face directly or indirectly engageable by said recock piston,wherein as said recock piston moves from said piston ready-to-fire position to said impacter-cocking position, said impacter moves from said valve-opening position to said cocked position, andwherein said recock piston returns to said piston ready-to-fire position while said impacter is restrained in said cocked position by said impacter sear;said pneumatic gun further comprising a member selected from the group consisting of:(i) a connecting rod, said connecting rod constraining said bolt and said recock piston to translate in concert, and(ii) a bolt connection bar, said bolt connection bar constraining said bolt to travel rearward when said recock piston travels rearward, andconstraining said recock piston to travel forward when said bolt travels forward;so that when said recock piston moves rearward to said impacter-cocking position said bolt moves rearward to said bolt open position, and so that when said bolt moves forward to said bolt ready-to-fire position said recock piston moves forward to said piston ready-to-fire position:whereby said impacter and said recock piston separately provide a valve opening function and a recock function, respectively, for said pneumatic gun.31. A hammer assembly for use in a pneumatic gun, said pneumatic gun for firing projectiles by use of compressed gas as a propellant, said pneumatic gun comprising:(1) a user actuable trigger;(2) a forward end and a rearward end;(3) a gas reservoir, said gas reservoir for containing compressed gas therein;(4) a valve, said valve normally closed and impact openable to release compressed gas from said gas reservoir, said valve comprising a rearwardly directed impact receiving face;(5) a recock chamber, said recock chamber comprising forwardly a sealable portion, said sealable portion in fluid communication with said valve so that when said valve is open a portion of the compressed gas released flows into said sealable portion,(6) an impacter sear, said impacter sear controlled by said user-actuable trigger;said hammer assembly comprising:(a) an impacter, said impacter slidably translatable within said recock chamber between a cocked position and a valve-opening position, said impacter forwardly biased toward said valve-opening position, said impacter comprising:(i) an impacter body portion;(ii) an impact imparting face, said impact imparting face forwardly directed, said impact imparting face acting on said impact receiving face when said impacter moves to said valve-opening position, so that momentum is provided by said impacter to open said valve;(iii) a forwardly-directed impacter contact face; and(iv) a forwardly-directed sear shoulder, said sear shoulder engageable on said impacter sear when said impacter is in said cocked position, so that said impacter is restrained in said cocked position until said impacter is released in response to actuation of said user-actuable trigger;(b) a recock piston, said recock piston slidably translatable within said recock chamber between a piston ready-to-fire position and an impacter-cocking position, said recock piston directly or indirectly biased forward toward said piston ready-to-fire position, said recock piston comprising:(i) a forwardly-directed pressure receiving face, said pressure receiving face slidable within said sealable portion of said recock chamber, said pressure receiving face responsive to the urging of the portion of compressed gas released into said sealable portion of said recock chamber to move said recock piston from said piston ready-to-fire position to said impacter-cocking position; and(ii) a longitudinal passageway, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal;said transfer portal located forward of said impacter body portion;said transfer portal slidably receptive therethrough of one or more members selected from the group consisting of: (A) an elongated nose portion of said impacter, said elongated nose portion comprising said impact imparting face, (B) a valve pin portion of said valve, said valve pin portion comprising said impact receiving face, and (C) a transfer pin;so that the momentum provided by said impacter to open said valve passes through said transfer portal;said impacter contact face directly or indirectly engageable by said recock piston,wherein as said recock piston moves from said piston ready-to-fire position to said impacter-cocking position, said impacter moves from said valve-opening position to said cocked position, andwherein said recock piston returns to said piston ready-to-fire position while said impacter is restrained in said cocked position by said impacter sear,whereby said impacter and said recock piston separately provide a valve opening function and a recock function, respectively, for said pneumatic gun.32. A firing mechanism for a pneumatic gun, said pneumatic gun comprising a frame, said frame comprising a forward end and a rearward end, said firing mechanism comprising:(a) a gas reservoir, said gas reservoir for containing compressed gas therein;(b) a recock chamber, said recock chamber comprising a forward end;(c) a valve, said valve having a normally closed position wherein the gas in said gas reservoir is prevented from flowing, and an open position wherein said valve permits flow of compressed gas out of said gas reservoir, and a portion of said compressed gas is allowed to flow into said recock chamber, said valve responsive to impact to transition from said closed position to said open position;(d) an impacter, said impacter forwardly biased and slidably translatable in said recock chamber between a rearward, cocked position and a forward, valve-opening position, said impacter comprising an impact imparting face;(e) a recock piston, said recock piston directly or indirectly forwardly biased in said recock chamber and slidably translatable therein between a forward piston ready-to-fire position and a rearward impacter-cocking position, said recock piston comprising:(i) a forwardly-directed pressure receiving face,(ii) a longitudinal passageway, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal, and(iii) a rearwardly directed recock piston contact face, said recock piston contact face directly or indirectly engageable on said impacter as said recock piston moves from said piston ready-to-fire position to said impacter-cocking position, so that said impacter moves to said cocked position;said impact imparting face of said impacter operable to impact said valve to actuate said valve from said closed position to said open position;said impacter forwardly slidable in said recock chamber independently from said recock piston when said recock piston is in said piston ready-to-fire position.33. A pneumatic gun for firing projectiles by use of compressed gas as a propellant, said pneumatic gun comprising:(a) a forward end and a rearward end;(b) a frame, said frame comprising a bolt chamber and a recock chamber;(c) a bolt, said bolt forwardly biased and slidably translatable within said bolt chamber between an open, projectile-loading position and a closed, bolt ready-to-fire position;(d) a firing chamber, said firing chamber adapted to hold a projectile for receipt of compressed gas to propel said projectile from said pneumatic gun;(e) a loading port in said bolt chamber, said loading port providing when said bolt is in said open, projectile-loading position, a passageway for entry of a projectile into a position in front of said bolt for transport of said projectile by said bolt to said firing chamber;(f) a gas reservoir, said gas reservoir for containing compressed gas therein;(g) a normally closed valve, said valve situated to control release of compressed gas from said gas reservoir, said valve including a valve seat and a valve seal displaceable from said valve seat, wherein said valve prevents the flow of gas through said valve seat when said valve seat is sealingly engaged by said valve seal, and wherein said recock chamber is in fluid communication with said valve and adapted to receive compressed gas therefrom;(h) a recock piston, said recock piston located in said recock chamber, said recock piston slidably translatable and forwardly biased in said recock chamber, said recock piston comprising:(i) a forwardly-directed pressure receiving face responsive to compressed gas received by said recock chamber, and(ii) a longitudinal passageway, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal;(i) an impacter, said impacter comprising an impact imparting face, said impacter located in said recock chamber, said impacter slidably translatable in said recock chamber from a rearward,cocked position to a forward, valve-opening position, said impacter biased toward said valve-opening position;said recock piston slidable in said recock chamber from a forward, piston ready-to-fire position to a rearward, impacter-cocking position;said impacter responsive to rearward movement of said recock piston, so that when said recock piston moves rearward to said impacter-cocking position, said impacter moves rearward to said cocked position, andsaid recock piston forwardly slidable to said piston ready-to-fire position while said impacter remains rearward in said cocked position;said valve seal responsive, directly or indirectly, to an impact from said impact imparting face of said impacter, to move from (1) a closed, sealed position to (2) an open, gas release position wherein gas is released, with one portion of the gas released provided into said recock chamber to move said recock piston rearward to said impacter-cocking position, which movement of said recock piston rearward (A) directly or indirectly moves said bolt rearward to said open, projectile-loading position, and (B) directly or indirectly moves said impacter rearward to said cocked position.34. A pneumatic gun for firing projectiles by use of compressed gas as a propellant, said pneumatic gun comprising:(a) a frame, said frame comprising a front end and a rear end;(b) a gas reservoir, said gas reservoir for containing compressed gas therein;(c) a normally-closed impact-openable valve, said valve situated to control release of compressed gas from said gas reservoir, said valve having a closed position wherein compressed gas in said gas reservoir is prevented from flowing, and an open position wherein said valve releases compressed gas from said gas reservoir, said valve comprising:(i) a valve body, said valve body comprising a rearwardly directed face, and(ii) a valve seat;(d) a recock chamber, said recock chamber defined within said frame rearward of said rearwardly directed face of said valve body; said recock chamber comprising forwardly a sealable portion;(e) recock gas porting, said recock gas porting fluidly directing one portion of the gas released by said valve to said sealable portion of said recock chamber;(f) propulsion gas porting, said propulsion gas porting fluidly directing another portion of the gas released by said valve to a projectile to be fired by said gun;(g) an impacter, said impacter slidably translatable in said recock chamber between a forward, valve-opening position and a rearward, cocked position, said impacter forwardly biased in said recock chamber toward said valve-opening position, said impacter comprising:(i) a forwardly-directed sear shoulder,(ii) an impacter body portion, and(iii) a forwardly-directed impact imparting face, said impact imparting face operable when said impacter moves to said valve-opening position to transfer momentum of said impacter to said valve and to actuate said valve from said closed position to said open position:(h) a recock piston, said recock piston slidably translatable in said recock chamber between a forward, piston ready-to-fire position and a rearward, impacter-cocking position, said recock piston forwardly biased in said recock chamber, said recock piston comprising:(i) a forwardly-directed pressure receiving face, said pressure receiving face slidable within said sealable portion of said recock chamber, and(ii) a longitudinal passageway, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal;said recock piston sufficiently responsive to force exerted by the portion of gas provided to said sealable portion of said recock chamber to recock said gun;said impacter body portion larger in transverse cross section than said transfer portal, and said impacter body portion positioned rearward of said transfer portal;so that when said recock piston moves rearward to said impacter-cocking position said impacter moves rearward to said cocked position, and so that said recock piston can move forward to said piston ready-to-fire position white said impacter is restrained in said cocked position.35. A pneumatic gun which uses compressed gas as a propellant for firing projectiles, said pneumatic gun comprising:(a) a frame, said frame comprising a front end, and a rear end;(b) a user-actuable trigger;(c) an impacter sear, said impacter sear operably linked to said user-actuable trigger;(d) a gas reservoir, said gas reservoir for containing compressed gas therein;(e) a normally-closed impact-openable valve, said valve situated to control release of compressed gas from said gas reservoir, said valve having a valve closed position wherein gas in said gas reservoir is prevented from flowing, and a valve open position wherein said valve releases gas from said gas reservoir, said valve comprising:(i) a valve body, said valve body comprising:(A) a rearwardly directed face, and(B) a valve seat;(ii) a valve stem, said valve stem comprising:(A) a seal body, said seal body comprising a rearwardly directed valve seal sealingly engageable with and forwardly displaceable from said valve seat, and(B) a valve pin, said valve pin terminating rearwardly in an impact receiving face;(f) a recock chamber, said recock chamber extending rearwardly within said lower cavity from said rearwardly directed face of said valve body, said recock chamber comprising forwardly a sealable portion;(g) recock gas porting, said recock gas porting fluidly directing one portion of the compressed gas released by said valve to said sealable portion of said recock chamber;(h) propulsion gas porting, said propulsion gas porting fluidly directing another portion of compressed gas released by said valve to a projectile to be fired by the gun;(i) an impacter, said impacter slidably translatable in said recock chamber between a rearward, cocked position and a forward, valve-opening position, said impacter biased toward said valve-opening position by an impacter power spring, said impacter comprising:(i) an impacter body portion,(ii) a forwardly-directed impacter contact face,(iii) an elongated nose portion, said elongated nose portion terminating forwardly in an impact imparting face, and(iv) a forwardly-directed sear shoulder, said sear shoulder receptive when said impacter is in said cocked position to engagement by said impacter sear to restrain said impacter in said cocked position;(j) a recock piston, said recock piston slidably translatable in said recock chamber between a piston ready-to-fire position and a rearward, impacter-cocking position, said recock piston comprising:(i) a forwardly-directed pressure receiving face, said pressure receiving face slidable within said sealable portion of said recock chamber, and(ii) a longitudinal passageway, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal;(k) a bolt chamber,(l) a loading port, said loading port when open accommodating the passage of a projectile into said bolt chamber;(m) a bolt, said bolt slidably translatable within said bolt chamber between a bolt ready-to-fire position and a rearward, bolt open position, said loading port open when said bolt is in said bolt open position, said bolt forwardly biased by a bolt spring;(n) a connecting rod, said connecting rod constraining said bolt and said recock piston to translate in concert, so that said recock piston is thereby forwardly biased within said recock chamber by said bolt;said recock piston sufficiently responsive to force exerted by the compressed gas provided to said sealable portion of said recock chamber to recock said gun;said impacter body portion located rearward of said transfer portal;said impacter body portion larger in transverse cross section than said transfer portal;said elongated nose portion fitting slidably through said transfer portal;said valve pin fitting slidably through said transfer portal;said impact receiving face of said valve pin receptive to impact by said impact imparting face of said elongated nose portion, so that forward momentum of said impacter is transferred through said transfer portal and imparted to said valve to actuate said valve from said valve dosed position to said valve open position;said impacter contact face of said impacter impingeable on said recock piston, so that when said recock piston moves rearward to said impacter-cocking position said impacter moves rearward to said cocked position, and so that said recock piston can move forward to said piston ready-to-fire position while said impacter is restrained in said cocked position.36. A pneumatic gun for firing projectiles by use of compressed gas as a propellant, said pneumatic gun comprising:(a) a frame, said frame comprising a front end and a rear end;(b) a gas reservoir, said gas reservoir for containing compressed gas therein;(c) a normally-closed impact-openable valve, said valve comprising an impact receiving face, said valve situated to control release of compressed gas from said gas reservoir;(d) propulsion gas porting, said propulsion gas porting directing one portion of the compressed gas released by said valve when said valve is open to a projectile to be fired by said pneumatic gun:(e) a recock chamber, said recock chamber comprising a forward chamber end, said recock chamber comprising at said forward chamber end a sealable portion, said sealable portion receptive of another portion of the compressed gas released by said valve when said valve is open:(f) an impacter, said impacter slidably translatable in said recock chamber between a cocked position and a valve-opening position, said impacter forwardly biased in said recock chamber toward said valve-opening position, said impacter comprising:(i) a forwardly-directed impact imparting face, said impact imparting face acting on said impact receiving face when said impacter moves to said valve-opening position, so that momentum is provided to said valve by said impacter to open said valve, and(ii) an impacter body portion;(g) a recock piston, said recock piston slidably translatable in said recock chamber between a forward, piston ready-to-fire position and a rearward, impacter-cocking position, said recock piston directly or indirectly forwardly biased in said recock chamber, said recock piston comprising:(i) a forwardly-directed pressure receiving face, said pressure receiving face slidable within said sealable portion of said recock chamber, and(ii) a longitudinal passageway, said longitudinal passageway penetrating said recock piston and said pressure receiving face and defining thereby a transfer portal in said pressure receiving face;said recock piston sufficiently responsive to force exerted by the portion of compressed gas provided to said sealable portion of said recock chamber to recock said pneumatic gun:said impacter body portion larger in transverse cross section than said transfer portal, and said impacter body portion located rearward of said transfer portal;so that the momentum provided by said impacter to open said valve passes through said transfer portal;and so that:(A) when said recock piston moves rearward to said impacter-cocking position, said impacter is thereby moved rearward to said cocked position, and(B) when said impacter is in said cocked position, said recock piston is forwardly slidable independently of said impacter, and(C) when said recock piston is in said piston ready-to-fire position, said impacter is forwardly slidable independently of said recock piston.37. A pneumatic gun for firing projectiles by use of compressed gas as a propellant, said pneumatic gun comprising:(a) a frame comprising a front end and a rear end;(b) a gas reservoir, said gas reservoir for containing compressed gas therein;(c) a normally-closed impact-openable valve, said valve situated to control release of compressed gas from said gas reservoir;(d) a propulsion gas porting, said propulsion gas porting directing one portion of the compressed gas released by said valve when said valve is open to a projectile to be fired by said pneumatic gun;(e) a recock chamber, said recock chamber comprising a forward chamber end, said recock chamber comprising at said forward chamber end a sealable portion in fluid communication with said valve, said sealable portion receptive of another portion of the compressed gas released by said valve when said valve is open;(f) an impacter, said impacter slidably translatable in said recock chamber between a cocked position and a valve-opening position, said impacter forwardly biased in said recock chamber toward said valve-opening position, said impacter comprising:(i) a forwardly directed impact imparting face, said impact imparting face operable to impact said valve when said impacter moves to said valve-opening position, so that momentum is provided to said valve by said impacter to open said valve,(ii) an impacter body portion, and(iii) an impacter contact face;(g) a recock piston, said recock piston slidably translatable in said recock chamber between a forward piston ready-to-fire position and a rearward impacter-cocking position, said recock piston forwardly biased in said recock chamber, said recock piston comprising:(i) a forwardly-directed pressure receiving face, said pressure receiving face slidable within said sealable portion of said recock chamber,(ii) a longitudinal passageway, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal;(h) a bolt chamber within said frame;(i) a loading port, said loading port when open accommodating therethrough the passage of a new projectile into said bolt chamber;(j) a bolt, said bolt slidably translatable and forwardly biased in said bolt chamber between a rearward, open position, wherein said loading port is open, and a forward, bolt ready-to-fire position, wherein said loading port is closed;said transfer portal slidably receptive therethrough of one or more members selected from the group consisting of: (A) an elongated nose portion of said impacter, said elongated nose portion comprising said impact imparting face, (B) a valve pin portion of said valve, said valve pin portion comprising said impact receiving face, and (C) a transfer pin;said impacter body portion larger in transverse cross section than said transfer portal, and said impacter body portion positioned rearward of said transfer portal, so that the impact provided by said impacter to open said valve passes through said transfer portal;said recock piston sufficiently responsive to force exerted by the gas provided to said sealable portion of said recock chamber to recock said gun;said impacter contact face directly or indirectly engageable by said recock piston, so that:(A) when said recock piston moves rearward to said impacter-cocking position, said impacter moves rearward to said cocked position, and(B) when said impacter is in said cocked position, said recock piston is forwardly slidable independently of said impacter, and(C) when said recock piston is in said piston ready-to-fire position, said impacter is forwardly slidable independently of said recock piston;said bolt constrained to travel rearward when said recock piston travels rearward, and said recock piston constrained to travel forward when said bolt travels forward, so that when said recock piston moves rearward to said impacter-cocking position said bolt moves rearward to said bolt open position, and so that when said bolt moves forward to said bolt ready-to-fire position said recock piston moves forward to said piston ready-to-fire position.38. A method of opening a normally-closed impact-openable valve in a pneumatic gun, said method comprising the steps of:(a) providing a gas reservoir, said gas reservoir for containing compressed gas in said pneumatic gun;(b) providing a recock chamber in said pneumatic gun;(c) positioning said valve in said pneumatic gun to control the release of compressed gas from said gas reservoir;(d) providing said valve with a valve seat;(e) providing in said pneumatic gun an impacter, said impacter slidably translatable in said recock chamber between a cocked position and a valve-opening position, said valve-opening position closer than said cocked position to said valve seat, said impacter restrainable in said cocked position, said impacter comprising an impacter body portion;(f) biasing said impacter toward said valve-opening position;(g) providing said valve with an impact receiving face, said impact receiving face receptive of impact by said impacter to open said valve;(h) providing in said pneumatic gun a recock piston, said recock piston slidably translatable in said recock chamber between a piston ready-to-fire position and an impacter-cocking position, said piston ready-to-fire position closer than said impacter-cocking position to said valve seat;(i) biasing said recock piston toward said piston ready-to-fire position;(j) providing a pressure receiving face on said recock piston, said pressure receiving face disposed between said impacter body portion and said valve seat;(k) providing a longitudinal passageway in said recock piston, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal;(l) restraining said impacter in said cocked position;(m) releasing said impacter to travel to said valve-opening position;(n) passing the momentum provided by said impacter through said transfer portal and to said valve;(o) opening said valve.39. A method of opening a normally-closed impact-openable valve in a pneumatic gun, said pneumatic gun comprising a forward end and a rearward end, said method comprising the steps of:(a) providing a gas reservoir, said gas reservoir for containing compressed gas in said pneumatic gun;(b) providing a recock chamber in said pneumatic gun;(c) positioning said valve in said pneumatic gun to control the release of compressed gas from said gas reservoir;(d) providing in said gun an impacter, said impacter slidably translatable in said recock chamber between a cocked position and a valve-opening position, said valve-opening position forward of said cocked position;(e) providing said impacter with an impacter body portion and a forwardly-directed sear shoulder:(f) biasing said impacter toward said valve-opening position;(g) providing in said gun an impacter sear, said impacter sear for restraining said impacter in said cocked position;(h) providing in said gun a user actuable trigger, said user actuable trigger operably linked to said impacter sear for releasing said impacter from said cocked position;(i) providing said valve with an impact receiving face, said impact receiving face receptive of impact by said impacter to open said valve;(j) providing in said gun a recock piston, said recock piston slidably translatable in said recock chamber between a piston ready-to-fire position and an impacter-cocking position, said piston ready-to-fire position forward of said impacter-cocking position;(k) biasing said recock piston toward said piston ready-to-fire position;(l) providing a forwardly-directed pressure receiving face on said recock piston;(m) positioning said impacter body portion rearward of said pressure receiving face in said recock chamber;(n) providing a longitudinal passageway in said recock piston, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal;(o) restraining said impacter in said cocked position;(p) releasing said impacter to travel to said valve-opening position;(q) passing the momentum provided by said impacter through said transfer portal and to said valve;(r) opening said valve.40. A method of operating a pneumatic gun, said gun comprising a forward end and a rearward end, said method comprising the steps of:(a) providing in said gun a gas reservoir, said gas reservoir for containing compressed gas;(b) providing in said gun a recock chamber,(c) providing in said gun a normally-closed impact-openable valve, said valve in fluid communication with said recock chamber and with said gas reservoir, said valve when open permitting release of compressed gas from said gas reservoir;(d) providing in said gun an impacter, said impacter slidably translatable within said recock chamber between a rearward, cocked position and a forward, valve-opening position;(e) providing said impacter with an impacter body portion, a forwardly-directed impact imparting face, a forwardly-directed impacter contact face and a forwardly-directed sear shoulder;(f) providing said valve with a valve seat, and with a rearwardly directed impact receiving face receptive to an impact by said impact imparting face when said impacter moves to said valve-opening position;(g) providing impacter bias, said impacter bias forwardly biasing said impacter;(h) providing in said gun an impacter sear, said impacter sear for restraining said impacter in said cocked position;(i) providing in said gun a user actuable trigger, said trigger operably linked to said impacter sear for releasing said impacter from said cocked position;(j) providing in said gun a recock piston, said recock piston slidably translatable within said recock chamber between a forward, ready-to-fire position and a rearward, impacter-cocking position;(k) providing a forwardly-directed pressure receiving face on said recock piston, said pressure receiving face disposed between said impacter body portion and said valve seat;(l) providing a longitudinal passageway, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal;(m) providing piston bias, said piston bias forwardly biasing said recock piston, either directly or indirectly;(n) restraining said impacter in said cocked position in preparation for firing;(o) moving said recock piston to said ready-to-fire position in preparation for firing;(p) releasing said impacter from said cocked position;(q) moving said impacter in response to said impacter bias to said valve-opening position;(r) passing momentum of said impacter through said transfer portal and to said valve;(s) opening said valve;(t) releasing compressed gas from said gas reservoir;(u) passing one portion of said released gas to a projectile to be propelled from said gun;(v) passing another portion of said released gas into said recock chamber;(w) moving said recock piston from said ready-to-fire position toward said impacter-cocking position in response to the urging of the portion of released gas passed into said recock chamber;(x) engaging said impacter contact face with said recock piston;(y) moving said recock piston to said impacter-cocking position,(z) moving said impacter to said cocked position;(aa) restraining said impacter in said cocked position; and(ab) moving said recock piston to said ready-to-fire position;so that said pneumatic gun is again ready to fire.41. A method of opening a loading port of a pneumatic gun for the introduction of a new projectile as said gun is being recocked after firing, and of subsequently closing said loading port and chambering said new projectile while leaving said gun cocked and ready to fire again, said gun comprising a forward end and a rearward end, said method comprising the steps of:(a) providing a bolt chamber in said gun:(b) providing in said gun said loading port, said loading port when open providing space to accommodate the passage of said new projectile into said bolt chamber forward of said bolt;(c) providing in said gun a bolt, said bolt slidably translatable within said bolt chamber between:(i) a rearward bolt open position, said loading port open when said bolt is in said bolt open position, and(ii) a forward bolt ready-to-fire position, said bolt closing said loading port when in said bolt ready-to-fire position, said bolt chambering said new projectile as said bolt moves from said bolt open position to said bolt ready-to-fire position;(d) providing in said gun a spring, said spring forwardly biasing said bolt;(e) providing in said gun a recock chamber;(f) providing in said gun a gas reservoir, said gas reservoir for containing compressed gas;(g) providing in said gun a normally-closed impact-openable valve, said valve openable in response to momentum of a forwardly-biased impacter moving forward from a cocked position, said valve when open releasing compressed gas from said gas reservoir, a portion of the released compressed gas flowing to said recock chamber to recock said gun;(h) providing in said gun a recock piston, said recock piston slidably translatable within said recock chamber between a forward, ready-to-fire position and a rearward, impacter-cocking position,(i) constraining said bolt to move rearward when said recock piston moves rearward;(j) constraining said recock piston to move forward when said bolt moves forward;(k) providing on said impacter a forwardly-directed impacter contact face, said impacter contact face engageable by said recock piston as said recock piston moves rearward to said impacter-cocking position;(l) providing on said recock piston a forwardly-directed pressure receiving face, said pressure receiving face receptive of the rearward urging of the compressed gas provided to said recock chamber;(m) providing a longitudinal passageway in said recock piston, said longitudinal passageway penetrating (A) said recock piston and (B) said pressure receiving face, to define in said pressure receiving face a transfer portal;(n) restraining said impacter in said cocked position in preparation for firing;(o) providing urging by said spring to move said recock piston to said piston ready-to-fire position, and said bolt to said bolt ready-to-fire position, in preparation for firing;(p) releasing said impacter to move forward from said cocked position;(q) passing the momentum of said impacter through said transfer portal to open said valve and release compressed gas from said gas reservoir,(r) passing a portion of the released gas into said recock chamber;(s) moving said recock piston rearward from said piston ready-to-fire position to said impacter-cocking position in response to the urging of the portion of compressed gas in said recock chamber;(t) imparting the rearward motion of said recock piston to said impacter to move said impacter to said cocked position;(u) imparting the rearward motion of said recock piston to said bolt to move said bolt to said bolt open position, opening said loading port and compressing said spring;(v) introducing said new projectile into said bolt chamber through said open loading port;(w) moving said bolt and said recock piston forward in response to the urging of said spring, chambering said new projectile and closing said loading port.42. The method as set forth in claim 41, wherein said gun further comprises a connecting rod, said connecting rod constraining said bolt and said recock piston to translate in concert.43. The method as set forth in claim 41, said gun further comprises a bolt connection bar, said bolt connection bar comprising a forwardly-directed bolt contact face, said bolt contact face engageable with said recock piston so that (A) when said recock piston travels rearward to said impacter-cocking position said bolt is pushed rearward to said bolt open position, and (B) when said bolt travels forward to said bolt ready-to-fire position, said recock piston is pushed forward to said piston ready-to-fire position.