HIGH STRENGTH POLYMER-BASED CARTRIDGE CASING AND MANUFACTURING METHOD

Technical Field

The present subject matter relates to ammunition articles with plastic components such as cartridge casing bodies, and, more particularly, to making ammunition articles with a frangible neck.

Background

It is well known in the industry to manufacture cartridge cases from either brass or steel. Typically, industry design calls for materials that are strong enough to withstand extreme operating pressures and which can be formed into a cartridge case to hold the bullet, while simultaneously resist rupturing during the firing process.

Conventional ammunition typically includes four basic components, that is, the bullet, the cartridge case holding the bullet therein, a propellant used to push the bullet down the barrel at predetermined velocities, and a primer, which provides the spark needed to ignite the powder which sets the bullet in motion down the barrel.

The cartridge case is typically formed from brass and is configured to hold the bullet therein to create a predetermined resistance, which is known in the industry as bullet pull. The cartridge case is also designed to contain the propellant media as well as the primer.

However, brass is heavy, expensive, and potentially hazardous. For example, the weight of 0.50 caliber ammunition is about 60 pounds per box (200 cartridges plus links).

The bullet is configured to fit within an open end or mouth of the cartridge case. Certain bullets, mainly for non-military uses, can include a groove (hereinafter referred to as a cannelure) formed in the mid section of the bullet to accept a crimping action imparted to the metallic cartridge case therein. When the crimped portion of the cartridge case holds the bullet by locking into the cannelure or onto the diameter, a bullet pull value is provided representing a predetermined tension at which the cartridge case holds the bullet. The bullet pull value, in effect, assists imparting a regulated pressure and velocity to the bullet when the bullet leaves the cartridge case and travels down the barrel of a gun.

Furthermore, the bullet is typically manufactured from a soft material, such as, for example only, lead. The bullet is accepted into the mouth of the cartridge, and then the cartridge alone is crimped to any portion of the bullet to hold the bullet in place in the cartridge case. Though, typically, the cartridge case is crimped to the cannelure of the bullet.

However, one drawback of this design is that the crimped neck does not release from around the bullet evenly when fired. This is partly due to the fact that the brass casing is not manufactured perfectly. The material thickness around the neck is slightly different causing the case to deform at slightly different rates thus allowing the bullet to be pushed slightly off center when coming out. This leads to uncertain performance from round to round. Pressures can build up unevenly and alter the accuracy of the bullet.

The propellant is typically a solid chemical compound in powder form commonly referred to as smokeless powder. Propellants are selected such that when confined within the cartridge case, the propellant burns at a known and predictably rapid rate to produce the desired expanding gases. As discussed above, the expanding gases of the propellant provide the energy force that launches the bullet from the grasp of the cartridge case and propels the bullet down the barrel of the gun at a known and relatively high velocity.

The primer is the smallest of the four basic components used to form conventional ammunition. As discussed above, primers provide the spark needed to ignite the powder that sets the bullet in motion down the barrel. The primer includes a relatively small metal cup containing a priming mixture, foil paper, and relatively small metal post, commonly referred to as an anvil.

When a firing pin of a gun or firearm strikes a casing of the primer, the anvil is crushed to ignite the priming mixture contained in the metal cup of the primer. Typically, the primer mixture is an explosive lead styphnate blended with non-corrosive fuels and oxidizers which burns through a flash hole formed in the rear area of the cartridge case and ignites the propellant stored in the cartridge case. In addition to igniting the propellant, the primer produces an initial pressure to support the burning propellant and seals the rear of the cartridge case to prevent high-pressure gases from escaping rearward. It should be noted that it is well known in the industry to manufacture primers in several different sizes and from different mixtures, each of which affects ignition differently.

The cartridge case, which is typically metallic, acts as a payload delivery vessel and can have several body shapes and head configurations, depending on the caliber of the ammunition. Despite the different body shapes and head configurations, all cartridge cases have a feature used to guide the cartridge case, with a bullet held therein, into the chamber of the gun or firearm.

The primary objective of the cartridge case is to hold the bullet, primer, and propellant therein until the gun is fired. Upon firing of the gun, the cartridge case seals the chamber to prevent the hot gases from escaping the chamber in a rearward direction and harming the shooter. The empty cartridge case is extracted manually or with the assistance of gas or recoil from the chamber once the gun is fired.

As shown in FIG. 1A, a bottleneck cartridge case 10 has a body 11 formed with a shoulder 12 that tapers into a neck 13 having a mouth at a first end. Note that the shoulder 12 has a uniform thickness, or width. Further, the angle of the shoulder 12 on the outside of the cartridge case 10 is the same as the angle of the shoulder 12 inside the case 10, denoted as α and θ, respectively. In the prior art, α=θ, and the shoulder angle a is dictated by the caliber of the cartridge. A primer holding chamber 15 is formed at a second end of the body opposite the first end. A divider 16 separates a main cartridge case holding chamber 17, which contains a propellant, from the primer holding chamber 15, which communicate with each other via a flash hole channel 18 formed in the web area 16. An exterior circumferential region of the rear end of the cartridge case includes an extraction groove 19a and a rim 19b.

Prior art patents in this area include U.S. Patent No. 4,147,107 to Ringdal U S. Patent No. 6,845,716 to Husseini et al., U.S. Patent No. 7,213,519 to Wiley et al., WO95/13516A1 and U.S. Patent No. 7,610,858 to Chung. The five patents are directed to an ammunition cartridge suitable for rifles or guns and including a cartridge case made of at least a plastics material. However, each has their own drawbacks.

Further, a technical report released in May 2005 by the Armament Research, Development and Engineering Center titled "Alternative Cartridge Case Material and Design" by J. S. Chung, et al. (the "Chung Paper") describes in detail the failings of certain polymers used in ammunition cartridges and cartridge designs known to the authors. Features and limitations are identified for cartridge, the polymer, and the molding process. Many drawbacks are noted.

Hence a need exists for a polymer casing that can perform as well as or better than the brass alternative. A further improvement are polymer casings that are capable of production in a more conventional and cost effective manner, i.e. by using standard loading presses and better manufacturing techniques.

Summary

The teachings herein alleviate one or more of the above noted problems with the strength and formation of polymer based cartridges.

A high strength polymer-based cartridge casing inclosing a volume, can include a first end having a mouth, a neck extending away from the mouth, and a shoulder extending below the neck and away from the first end. A projectile can be disposed in the mouth and a frangible portion can be disposed on the neck, which is capable of being split upon discharge of the projectile. In an example, the split of the frangible portion prevents a second projectile from being disposed in the mouth.

The frangible portion can be, at least, a cut-out, a reduced thickness of the neck, a scallop in the neck, or a perforated seam. The frangible portion can be disposed on an inside or outside of the casing, and can extend to approximately the shoulder.

A method of making a high strength polymer-based cartridge casing can have the steps of molding a component using a polymer. The molding step can include molding a first end having a mouth and a second end opposite the first end. Steps also include molding a neck extending away from the mouth, molding a shoulder extending below the neck and away from the first end; and forming a frangible portion on the neck capable of being split.

The method may have the step of forming at least one of a cut-out, a reduced thickness of the neck, a scallop in the neck, or a perforated seam and forming the frangible portion on an inside or outside of the neck. Further, the frangible portion can be formed approximately to the shoulder.

Brief Description of the Drawings

The drawing figures depict one or more implementations in accord with the present teachings, by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements.

• FIG. 1A is a cross sectional view of a conventional bottleneck cartridge case;
• FIG. 1B is a side view of a conventional bullet with cannelure;
• FIG. 2 is a side perspective view of the outside of an example of a cartridge case;
• FIG. 3 is a longitudinal cross-section of the upper component of the cartridge;
• FIG. 4 is a bottom, side, perspective, radial cross-section of the upper and lower components of the cartridge;
• FIG. 5 is an end view of the upper component without the lower component and insert;
• FIG. 6 is a side view of the lower component without the upper component and insert;
• FIG. 7 is a bottom front perspective view of the lower component of FIG. 6;
• FIG. 8 is a longitudinal cross-section view of the lower component of FIG. 6;
• FIG. 9 is a side view of the insert without the upper and lower components;
• FIG. 10 is a bottom front perspective view of the insert of FIG. 8;
• FIG. 11 is a longitudinal cross-section view of the insert of FIG. 8;
• FIG. 12 is a longitudinal cross-section view of a further example of a cartridge case;
• FIG. 13A is a top, side , perspective view of the upper component of the further example;
• FIG. 13B is a longitudinal cross-section of another example of the upper component of the cartridge;
• FIG. 13C is a longitudinal cross-section of the example of the upper component of the cartridge of FIG. 13B with a projectile;
• FIG. 14 is a longitudinal cross-section view of another example of a ribless cartridge;
• FIG. 15A is a top, side perspective longitudinal cross-section view of a portion of an upper component with a relief;
• FIG. 15B is a longitudinal cross-section view of the insert of FIG. 14;
• FIG. 16 is a longitudinal cross-section view of an example of a straight wall cartridge case;
• FIG. 17 is a longitudinal cross-section view of the cartridge case of FIG. 2;
• FIG. 18 is a longitudinal cross-section view of the lower component and insert under pressure;
• FIG. 19 is a flow-chart of an example of the manufacturing method of a cartridge case;
• FIG. 20 is a is a top, side, perspective view of the upper component of another example;
• FIG. 21 is a top, side perspective longitudinal cross-section view of a portion of an upper component of FIG. 20; and
• FIG. 22 is a top, side perspective view of the frangible upper component after firing.

Detailed Description

In the following detailed description, numerous specific details are set forth by way of examples in order to provide a thorough understanding of the relevant teachings. However, it should be apparent to those skilled in the art that the present teachings may be practiced without such details. In other instances, well known methods, procedures, components, and/or circuitry have been described at a relatively high-level, without detail, in order to avoid unnecessarily obscuring aspects of the present teachings.

The present example provides a cartridge case body strong enough to withstand gas pressures that equal or surpass the strength required of brass cartridge cases under certain conditions, e.g. for both storage and handling.

Reference now is made in detail to the examples illustrated in the accompanying drawings and discussed below. FIG. 2 illustrates an example of a cartridge case 100. The cartridge case 100 includes an upper component 200, a lower component 300, and an insert 400. In this example, the upper component 200 and the lower component 300 are made of a polymer, while insert 400 is made from a metal, an alloy of metals, or an alloy of a metal and a non-metal. Regardless of materials, the outer dimensions of the cartridge case 100 are within the acceptable tolerances for whatever caliber firearm it will be loaded into.

The polymer used is lighter than brass. A glass-filled high impact polymer can be used where the glass content is between 0%-50%, preferably between 5% and 20%. In another example the glass content can be 10% and another of 15%. An example of an impact modified nylon polymer without the glass content is BASF's Capron^® BU50I. The insert 400 can be made of steel, and, in an example, heat treated carbon steel, 4140. The 4140 steel has a rating on the Rockwell "C" scale ("RC") hardness of about 20 to about 50. However, any carbon steel with similar properties, other metals, metal alloys or metal/non-metal alloys can be used to form the insert. Heat treating a lower cost steel alloy to improve its strength is a point of distinction from the prior art, which have typically opted for more expensive alloys to deal with the strength and ductility needed for a cartridge casing application.

FIGs. 20, 21 and 22 illustrate an example of an upper component 800. The upper component 800 includes a first end 810 having a mouth 808 to receive a projectile (not illustrated). Below the mouth 808 is a neck 806 and shoulder 804. The neck 806 has one or more frangible portions 860 which can include, at least one of, cut-outs, reduced material wall thickness, scallops, or perforated seams. The frangible portion 860 is designed such that the neck 806 can tear or split along the frangible portions 860 when the cartridge is fired. The tears 865 in the frangible portion 860 are caused by the pressures formed in the cartridge on firing. The frangible portion 860 is designed to withstand the rigors of a normal cartridge but not to withstand these pressures.

The tears 865 can render the upper component 800 of the cartridge unsuitable for reloading purposes. This creates a one-time use cartridge. The frangible portions 860 can be in any number or size around the circumference of the neck 806 and can extend a short distance or extend a significant distance toward the shoulder 804. The frangible portions 860 can also be on the outside of the neck 806, or an alternating outside/inside pattern. Further, the frangible portion 860 can be in a spiral shape.

As noted, the mouth 808 having the frangible portion 860 is initially capable of being loaded and retaining a projectile as a normal cartridge does. The frangible portion 860 also does not affect the discharge of the projectile on firing. Further, the frangible portion 860, in one example, does not splinter or leave any portion unattached to the cartridge as a whole. In this way, the tearing of the frangible portion 860 does not interrupt, or hinder, the cartridge extraction after the projectile is fired.

In an example, the frangible portion 860 remains attached to the upper component 800 and can open, after projectile discharge, like the petals of a flower. On the initial firing and extraction, this is not a problem. The chamber of the weapon has such small tolerances to fit the cartridge, that the frangible portion 860, even while split along the tears 865, cannot "open" fully. The frangible portion 860 also does not inhibit extraction since the extracting force is rearwards, which has the effect of keeping the frangible portions 860 together, as opposed to separating them. Once the cartridge is extracted, the frangible portions 860 can expand. See, FIG. 22.

This expansion then causes a number of problems, which makes the cartridge unsuitable for reloading. Problems include that the neck 806 is naturally weakened, which can cause problems when the second projectile is both seated and fired. The diameter of the neck 806 is expanded, making it difficult to properly seat a projectile. This also causes problems chambering the reloaded cartridge. The tolerances between the chamber and cartridge are such that the expanded neck 806 cannot fit into the chamber. Additionally, the force of loading the reloaded cartridge into the chamber can cause the weakened neck 806 to expand, since forces are pushing the edges outward.

A further example can be that the frangible portion 860 detaches from the upper component 800 entirely. In this example, the frangible portions 860 exit through the muzzle of the barrel of the weapon. The frangible portions 860 can be carried down barrel by the gas that is created on firing and that is propelling the projectile. The frangible portions 860 can be outside the chamber before the next cartridge is loaded into the chamber.

Yet another example of preventing the reloading of a cartridge can include weakening the weld between a "short" upper component 800 and the lower component 300. In this example, the upper component 800 itself separates from the lower component 300 upon the firing of the projectile. The lower component 300 is extracted by the usual means and the upper component 800 exits through the muzzle, as discussed above. Once the upper component 800 separates from the lower component 300, the pressures generated by the gasses are such that the upper component 800 "folds," collapses, or changes shape significantly enough to fit down the barrel of the weapon and exit the muzzle. Again, both the portions of the cartridge are out of the chamber before the next cartridge is loaded.

Further to the separating upper component example, to facilitate the collapse of the upper component, a weakened seam can be added. This is a frangible portion 860 that can extend longitudinally from the mouth 808 to past the shoulder 804, or any lengths in between. The seam splits upon firing, allowing the upper component to collapse more easily to assure discharge out the muzzle of the barrel.

In another example, the frangible portion 860 can be, or formed with, the relief 250 described above. The relief 250 can be formed thin enough to act as the frangible portion 860 after firing of the projectile. Note that the frangible portion 860 can be included in both ribbed and smooth (ribless) examples, along with both bottleneck and straight cartridges (noted below).

The forming of the frangible portion 860 can be, in one example, done at the time of molding the upper component 800 (see below for manufacturing methods). Alternately, after the upper component 800 is molded, the frangible portion 860 can be created by mechanical or chemical processes to create the weakened sections. For example, the neck 806 could be etched with a solvent to form any particular frangible pattern. Also, for example, the neck 806 can be mechanically perforated or have the neck wall thickness reduced. The frangible portion 860, regardless of its formation method, can be capable of withstanding normal handling of a cartridge and only split/tear after projectile discharge.

Note that the above examples illustrated a bottleneck cartridge. Many of the features above can be used with any cartridge style, including straight wall cartridges used in pistols. FIG. 16 illustrates an example of a straight wall cartridge 500. The straight wall cartridge 500 is a one-piece design of all polymer. The cartridge 500 has a body 502 and a mouth 508 at a first end 510. The walls 518 of the cartridge casing has ribs 516 along a majority of it length. The ribs 516 are similar in size, and shape to the ribs 216 described above. Also, the ribs can be excluded for a smooth straight wall example similar to the examples in FIGs. 12 and 14.

The ribs 516 are dimensioned and shaped pursuant to the requirements of the particular caliber. To that end, the ribs 516 begin set back from the first end 510 based on the depth the rear of the bullet sits in the cartridge. Further, in this example, as the walls transition into a lower bowl 514, the ribs 516 extend into the bowl. This aids in the strength of a back end 512 of the cartridge 500, since this example lacks a hardened metal insert.

The lower bowl 514 curves downward toward a flash hole 517 which then opens to a primer pocket 519. Both are similar to the features described above. Further, the back end is molded to form a rim 506.

Turning now to an example of forming the cartridge case 100, FIG. 17 illustrates a cross-section of all three elements engaged together to illustrate how they interface with each other. While the below example of the method is explained sequentially, one of ordinary skill in the art is aware that one or more steps can be performed either in sequence or in parallel.

The insert 400 is formed from a metal, metal alloy or metal/non-metal alloy. It can be formed by any known method in the art, including milling, hydroforming, casting, etc. All of the features of the groove 404, rim 406, ridges 410, keys 412, primer pocket 416, flash hole 418, basin 420 and ring 422 can be formed at the same time or over a series of steps. The insert 400 is then placed is a mold to be overmolded by the lower component 300.

As the lower component 300 is overmolded onto the insert 400, the liquid polymer spreads along two paths. One path spreads to the outside of the of the insert 400, engages around the ridges 410 and forms the bands 320 and sheath 316. The second path spreads to the inside of the insert 400 and flows down basin 420. This polymer flow forms the inner bowl 314. The second polymer flow is stopped by ring 422 which prevents any of the polymer from flowing into the flash hole 418. This has the effect of forming hole 312. It is the shape of the basin 420 and the ring 422 that act as a mold for a portion the inner bowl 314 and the hole 312. Further, preventing polymer from flowing into the flash hole 418 maintains the proper dimensions of the flash hole 418 which is important in igniting the powder and makes for a more reliable cartridge.

The remainder of the inner wall 310, the tapered portion 306 and the collar 308 of the lower component 300 are also formed during the overmolding process, but through the forms of a mold and not as a function of the contours of the insert 400, in this particular example.

For this example, in a separate process, the upper component 200 is also formed from a polymer. This can be the same polymer used in the lower component 300, as it is in this example, or they can be formed from separate polymers. Herein, the overlap portion 222, ribs 216, wall 218, shoulder 204, neck 206, lip 214, and mouth 208 are all formed as one piece. The ribs 216 aid in the flow of the polymer and glass additive during the molding process by providing more gap for the glass and polymer to flow through. Without ribs, the wall 218 can be formed thin and the glass additive in the polymer has difficulty in dispersing evenly throughout the entire component. The upper component 200 and the lower component 300/insert 400 overmolded piece are then bonded together. As noted above, the interface between the upper 200 and lower 300 components can be joined by any method known to those of skill in the art, including an ultraviolet (UV) light or heat cured resin, a spin weld, a laser weld or an ultrasonic weld.

The specific outer dimensions of the three elements and certain inner dimensions (e.g. mouth 208, lip 214, flash hole 418, and primer pocket 416) are dictated by the caliber and type of the firearm and type of ammunition. The cartridge casing 100 of the present example is designed to be used for any and all types of firearms and calibers, including pistols, rifles, manual, semi-automatic, and automatic firearms.

The present cartridge casing 100, as well as a typical cartridge casing made of brass, is typically not designed to withstand the pressures generated by the explosion of the powder within when the cartridge is outside the chamber of a firearm. Once inside the chamber, as the cartridge casing expands under the pressures of the explosion, the walls of the chamber support the casing and contain the pressures. This happens without rupturing the casing. The present examples take advantage of this fact to provide a stronger, lighter weight casing that improves accuracy and decreases the amount of powder needed.

FIG. 18 illustrates one advantage of the overmolded design of the lower component 300 and the insert 400. When the primer is struck, igniting the powder residing in the lower 300 and upper 200 components, the explosion of the powder generates gasses. The gasses cause a pressure that can expand the cartridge casing in both the longitudinal and radial directions. In the present example, radial pressures Pr act on the lower bowl 314 and the inner wall 310. The pressures Pr act normal to whatever surface they encounter. This pressure forces the inner bowl 314 against the basin 420. As the casing expands it encounters the chamber of the firearm, which in turn provides support for the casing. The sheath 316 of the lower component 300 contacts the chamber and provides a counter force Fc to the pressures Pr. The two forces provide a compression force or a "pinching" effect. Thus, the insert 400 engages the lower component 300 with increased strength allowing the overmolded components to stay together under the high pressures. For this example, the compression forces are further used to the advantage that the casing is typically still under pressure when it is removed from the chamber by the extractor (this is very typical when the ammunition is being fired from an automatic weapon). This additional strength helps assure that the cartridge case 100 remains intact as it is extracted.

A further exemplary effect of the pinching forces is that since the inner bowl 314 and basin 420 are forced closer together, this acts like a gasket, preventing the gasses from getting between the lower component 300 and the insert 400. If gases get between the two elements, this could separate the two, leaving the majority of the cartridge casing in the chamber while the insert 400 is extracted. This would cause the firearm to jam and fail.

An exemplary construction of the upper component 200 also aids in withstanding the pressures generated. As noted above, the ribs 216 increase the strength of the wall 218 of the upper component 200. In the present example, the upper component 200 accounts for anywhere from 70% to 90% of the length of the cartridge casing 100. A reduction in weight of the upper component 200 greatly affects the weight of the empty cartridge case 100. The ribs 216 provide strength for a minimal loss of powder capacity or increase in weight. Prior art designs increased the entire thickness of the wall 218, thus adding more weight than necessary.

Material and manufacturing examples noted throughout the above. The figures below describe another example of the method of manufacturing the polymer casing described above. Portions of the method described below can be performed either in series or in parallel.

Fig. 19 illustrates an exemplary manufacturing method. As an example, the insert 400 can be formed 4140 steel. The 4140 steel can start as bar stock and be machined down and stamped to the proper dimensions (step 600). The 4140 steel has a hardness high enough that the material does not require heat treatment after machining. However, the high hardness makes machining more difficult and expensive. Both 12L14 and 1015 steels can be used. Both are "softer" than the 4140 steel and that makes them easier to machine. However, after machining, the inserts need to be heat treated to increase their hardness so as to withstand the stresses during firing (step 602). Further, regardless of the steel chosen, the insert can be plated to reduce/resist corrosion (step 604). In one example, the insert can be plated with yellow zinc to a thickness of approximately 0.0005".

In a further example of the machining method, the stop 405 and the rim 406 have the same outer diameter. The matching diameters assist in the machining process. These two points provide sufficient surface area to properly hold the insert as its being formed. The transition between the groove 404 and the stop 405 can be a gradual transition with a sloping increase in diameter, or a more direct and steeper angle, even vertical. The step 405 acts as a rear "shutoff" to the overmolded area 408 during molding, so the molten polymer stops short of the extraction groove 404.

Once the insert is formed, the lower component can then be molded (step 606). In the example illustrated in FIG. 14, the lower component is approximately 1/3 the length of a total length of the cartridge. In other examples, the lower component can be upwards of 2/3 of the total length. The length ratio of the upper and lower components do not materially affect the molding process other than to change the size of the mold.

After the lower component 300 is molded to the insert 400, the piece is inspected to make sure it meets standards (step 608). The inspection, in one example, can be performed by a video inspection system that can determine if the insert 400 is properly overmolded and that the first end 302 is sufficiently round, and not oblong, in cross-section. Other standards are discussed below.

While the insert 400 and the lower component 300 are being machined and molded, in one example, the upper component 200 can be molded as well (step 610). The polymer used in molding the lower component can be the same, or different from the polymer used for the upper component. Similar to the lower component 300, the upper component 200 can also be inspected (step 612). In one example, both the mouth 208 and the second end 212 can be checked for roundness, among other standards.

Once both the upper and the lower components have been inspected, in this example, the two components can be bonded together. In this example, the bonding can be by UV laser welding (step 614). The roundness of the second end 212 and the first end 302 facilitate this process since the two components must be fitted together before the welding. Once the welding is complete, the casing 100 is inspected again to verify that the casing meets standards (step 616).

Once inspected, the casing is ready for loading. In this stage, the primer is inserted into the primer pocket 416, the powder is filled into the casing (i.e. the inside of the upper and lower components 200, 300) and the bullet is inserted into the mouth 208 (step 618). The type of primer and bullet and type and quantity of powder are dictated by the caliber being produced and the performance requirements for that caliber or round. Different type of bullets can be used depending if the bullet is used for commercial or military use. In another example, the amount of powder required in the cartridge case of the present example as opposed to a brass cartridge case can differ, as explained below.

After the bullet is set in the casing, an adhesive can be applied (step 620). The adhesive is applied to the mouth 208 and wicks in to surround the bullet in the relief 250. As noted above, the adhesive can have numerous purposes, or not used at all. Either after the bullet insertion or after the adhesive is applied, the finished round can be inspected one last time (step 622) prior to being boxed and ready for sale.

The intermediate inspections determine the "fitness" of the individual components. That is, their actual dimension relative to the specified norm and whether or not the components are acceptable to be assembled. At the final inspection of the assembled round, one or more other criteria can be used. For example, categories such as "Match," "Commercial," and "Non-Conforming." This permits separation for the absolute best of the best round in terms of shape and seal, the average rounds that are within tolerance, but a broader deviation, and the ones that are rejected and considered "failed". The "match" and "average" grades can be sorted and separately boxed, allowing for a price differential between the two types of rounds. Failed cartridges can be disposed of, and depending on the particular defect, certain components may be re-used. The failed cartridges can also undergo yet another inspection (or this can be included in the final inspection as a fourth category) to determine if the "failed" cartridge is still useable, i.e. the round has a strictly cosmetic flaw. The still useable cartridge can be sold as a "factory second" at a lower price.

In one example, the process above can result in components with a particular length and wall thickness. Table 1 below sets forth some of these dimensions. The length is the length in inches of the particular component for the particular caliber. The wall thicknesses are some of the thinnest portions of the cartridge wall, typically taken at about 1/2 to 2/3 of the length of the component. The wall length and wall thickness ratio is helpful when looking at the types of polymers and pressures necessary to injection mold the components.

Caliber

Upper (200)

Lower (300)

Thickness (in)

Length (in)

L/D

Thickness (in)

Length (in)

L/D

5.56

0.0188

1.43

76

0.02

0.31

16

.308

0.025

0.825

33

0.025

1.145

46

300WM

0.03

2.02

67

0.025

0.672

27

338LM

0.037

1.03

28

0.039

1.762

45

50 BMG

0.035

1.275

36

0.039

2.577

66

More examples of the above method are below. One example of molding the lower component is to place the insert into the mold, and inject the polymer to overmold the overmolded area 408 of the insert and form the remaining features. One element formed is the inner bowl 314 as it is shaped against the basin 420. The ring 422 of the insert 400 acts as dam and prevents any polymer from flowing into the flash hole 418 and primer pocket 416. This is also discussed above.

In another example, the only required difference between the upper and lower components' polymers is an additive that makes one of the polymers either opaque or transparent to particular wavelengths of light. In the example illustrated in FIG. 14, the outer tapered portion 342 can be transparent to UV laser light to allow it to pass to the opaque underskirt portion 240. This allows the laser's energy to heat the underskirt portion 240 and the upper and lower components can be welded together. One additive to make the polymer opaque, to at least UV light, is carbon black. Thus, numerous additives can be included in one or both of the polymer mixes to change the color or pattern of the upper or lower components.

The change in the color or pattern of the cartridge can be used to signify different types of loads. For example different colors can designate different bullet weights, performance, subsonic rounds, blank rounds, etc. Currently, when in military use, the tip of the bullet can be painted. However, paint can rub off or come off when firing, and the paint can cause fouling of the weapon. In contrast, the color change in the present example can be inherent in the manufacturing of the cartridge. The color differential can also be extended to the insert 400. The insert itself can be colored or plated with a different color.

The upper component is also molded, in one example, out of polymer. As noted above, the polymer used is lighter than brass. An example of an impact modified polymer is BASF's Capron^® BU50I. In an example, the high impact polymer can be mixed with fibers to increase its strength. Examples include glass fibers, carbon fibers, nanoclay, and carbon nanotubes. The fiber content of the polymer can be between 10-50% and 5-20% depending on the type of fiber and length of the fiber. In one example, the polymer for the upper and lower components can contain 10 % or 15% short glass fibers. Other polymers include PP, PA6, PA66, PBT, PET, thermoplastic polyurethane, polyamide, nylon 6, 66, nylon 12, nylon 12 copolymers, PA610, PA612, LCP, PPSU, PPA, PPS, PEEK, PEKK, polyester copolymers, PSU, PAEK and PES.

Another advantage of the polymer described above is that it expands uniformly in both the radial/lateral direction and the longitudinal direction. The longitudinal expansion of the polymer, combined with the ribbed design expands better than a brass cartridge. The neck 206 and/or shoulder 204 (depending on the type of cartridge, i.e. bottleneck, straight wall, etc.) expands forward toward the barrel, as well as outward in the radial direction. The cartridge casing 100 expands more effectively than brass, this forms a tighter seal between the cartridge and the barrel. In one example, none of gases expelled out the mouth 208 of the cartridge 100 passed backwards past the shoulder 204.

A experiment performed with 5.56 caliber ammunition of the illustrated example showed no residue from the shoulder back toward the rear of the cartridge. This is the proof that no gas passed the seal formed by the cartridge on firing. Similar results with a brass cartridge can usually only occur if the brass is hand loaded and fire formed to a specific gun chamber.

The tighter seal provided by the cartridge case of the present example means that more gas is used to propel the bullet. This can lead to higher muzzle velocities with the same amount of powder used in a brass casing. Said differently, the same muzzle velocities as provided by a standard brass cartridge can be achieved in one example of the present invention using less powder. At the rate at which ammunition is mass produced, this can lead to a significant cost savings. Alternately, the same firearm can now fire a bullet a farther distance and/or the impact has more kinetic force.

The tighter seal provided by the exemplary cartridge case also reduces fouling in the chamber which increases reliability of the firearm. Reduced fouling also extends the periods between when the firearm needs to be cleaned, extending its active service cycle.

Another advantage of the polymer design is its insulation properties. The polymer disclosed herein is a superior insulator to brass. This leads to a number of advantages. An advantage during firing is that less heat can be transferred to the cartridge/chamber. This can provide more energy to propel the bullet, since the energy is not heating its surroundings. This can also be a cause for the greater muzzle velocities discussed above. This is evidenced by observational data in which brass extracted from a firearm is very hot to the touch while, in contrast, the polymer rounds can be handled without discomfort immediately after being extracted from the chamber.

Less heat exchanged to the chamber can lead to a longer service life for the chamber/firearm. Constantly heating and cooling metals can alter their properties. Further, more rounds can be fired through the barrel before it becomes too hot, where high heat can lead to "baking" the fouling in the barrel which in turn can result in a significant loss of accuracy.

Another benefit of a better insulated cartridge case is that it can insulate the powder from the external storage temperatures. Preventing the temperature of the powder from deviating greatly aids in consistent ballistic performance. Studies have been performed linking changes in the peak pressures generated to changes in the temperature of the powder in the cartridge (see, for example http://www.shootingsoftware.com/ftp/Pressure%20Factors.pdf, last visited January 12, 2011).

The polymer construction of the cartridge case also provides a feature of reduced friction between the cartridge and chamber of the firearm. Reduced friction leads to reduced wear on the chamber, further extending its service life.