SHIM SUPPORTED UPON A PIVOT PIN BETWEEN UPPER AND LOWER RECEIVERS OF AN AR-15/M16/M4 STYLE FIREARM AND FOR REDUCING MISALIGNMENT AND PLAY

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention claims the priority of U.S. Ser. No. 61/530,429 filed Sep. 2, 2011.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention teaches an improved shim stock design, improving upon prior art disc shaped shims. The improved shim exhibits a thin arcuate body with a flat bottom which matches the profile of either of the spaced apart ears associated with the lower receiver and between which seats a tubular shaped and downwardly extending protrusion associated with the upper receiver. The shim can be employed either singularly or in a plural/stackable fashion and in order to eliminate the existence of excess tolerance (spacing) exhibiting between the upper and lower receives, such as which is further characterized as “slop” or “play” and which can otherwise result in misalignment between the receivers.

2. Background of the Relevant Art

Firearms such as the M16/M4/AR15 rifle include upper and lower receivers assembleable receivers which, upon assembly, engage at both a rear barrel location of the upper receiver which seats within an upper projecting annular support of the lower receiver which is proximate its stock, as well as at a forward location in which a cross wise apertured and underside extending lug associated with the upper receiver is aligned between outer apertures formed in a pair of spaced apart ears associated with an upper surface of the lower receiver. A pin is laterally displaced through the aligning apertures in order to affix the upper and lower receivers together.

A problem commonly associated with such assembled receivers is the incidence of “slop” or “play” and which is defined as any degree of looseness in the tolerance established between the aligning lugs and ears. Such looseness in the inter-fitting of the parts can be the cause of undesirable rattling or noise.

One solution proposed for addressing looseness between the mounting locations of the upper and lower receivers includes the installation of shims for taking up the excess lateral dimension, such as is depicted by the AR-15/M16 receiver shims produced by Brownells. The Brownells shim depicts a thin walled washer style configuration constructed of a tempered stainless steel for reducing side-to-side play between the receiver halves and the hammer/trigger components.

SUMMARY OF THE PRESENT INVENTION

The present invention discloses an improved shim stock design insertable between a mounting location established between upper and lower assembleable receivers of a firearm. As described, a first (typically lower) of the receivers exhibits a pair of spaced apart ears, each of which exhibiting an arcuate profile with a level base surface.

A pair of widthwise aligning apertures extend through the ears. The other of the receivers (typically upper) exhibits a generally cylindrical shaped projection aligning between said spaced apart ears, a widthwise extending aperture defined through the cylindrical shaped portion and which communicates with the aligning apertures in the ears.

The improved shim construction incorporates a thin body exhibiting a profile generally matching a selected ear and including an arcuate perimeter with an flat interconnected base surface. The body exhibits an aperture defined therein such that, upon placement between an inner facing surface of a selected ear and the intermediate positioned cylindrical shaped portion and subsequent widthwise traversing installation of a pivot pin, the body is sandwiched between the receivers and occupies an excess tolerance, thereby reducing or eliminating instances of misaligning slop or play exhibited between the receivers.

Additional features include the shim exhibiting a thickness in a range of 0.001″ to 0.010″. A plurality of shims can be provided as a kit and which are applied in scalable fashion to compensate for varying excess tolerance established between the receivers.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the attached drawings, when read in combination with the following detailed description, wherein like reference numerals refer to like parts throughout the several views, and in which:

FIG. 1 is a close up exploded view of a forward pivot pin arrangement established between upper and lower receivers of an AR15 type firearm, this interpreted as including both M16 and M4 variants, and including spaced apart ears associated with the lower receiver and between which seats a tubular shaped and downwardly extending protrusion associated with the upper receiver for enabling a widthwise displacing pin in alignment with mating apertures established between the ears and central protrusion to engage the receivers together;

FIG. 2 is a rotated view of the upper and lower receivers in separated fashion as shown in FIG. 1;

FIG. 3 is a perspective view of a separated lower receiver and depicting both the forward pivot pin and rearward spaced take down pin;

FIGS. 4A and 4B are successive disassembly views of the upper and lower AR15 receivers and depicting the unique shim stock design of the present invention;

FIG. 5 illustrates the unique shim stock shape, such as exhibiting a 0.004″ thickness, and which generally matches the profile of a selected ear associated with the lower receiver take down pin;

FIG. 6A is a pre-assembly view similar to that shown in FIGS. 1 and 2 depicting the upper receiver lugs and lower receiver ears in an aligned and pre-installed position;

FIG. 6B is a similar illustration to that shown in FIG. 6A and depicting a multiple shim arrangement arranged in stackable fashion according to a further embodiment;

FIG. 6C illustrate a successive assembly steps for positioning the unique shim stock portion on the lower receiver ear concurrent with assembling the upper receiver tubular potion such that the shim stock is sandwiched therebetween;

FIGS. 6D and 6E illustrates progressive assembly steps in which the upper and lower receivers are progressively assembled; and

FIG. 6F illustrates a further progressive assembly step in which the pivot pin is progressively displaced inwardly across the widthwise extending and aligned components of the upper and lower receivers with the shim stock installed in place in order to reduce or eliminate the instance of play or slop exhibited between the assembled receivers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention teaches an improved shim design which improves upon prior art disc shaped shims. As will be described in reference to the succeeding description, the improved shim exhibits a thin arcuate body with a flat bottom which matches an inner facing profile of either of the spaced apart ears associated with the lower receiver, and between which seats a tubular shaped and downwardly extending protrusion associated with the upper receiver. The shim can be employed either singularly or in a plural/stackable fashion and in order to eliminate the existence of excess tolerance (spacing) exhibiting between the upper and lower receives, such as which is further characterized as “slop” or “play” and which can otherwise result in misalignment between the receivers.

By controlling the slop existing between the upper and lower receivers at the front mounting location (the takedown pin defining a second rearward spaced mounting location), the firearm (rifle) can be easily disassembled in a field environment in order to perform any required remedial action (cleaning/clearing obstruction/repair). The shim stock also helps to maintain the normal operation of both the pivot and takedown pins while controlling potential inter-misalignment (again slop) in both rotational and horizontally mounted instances.

The shim stock, see as best shown at 10 in FIG. 5 includes a thin piece of metal stock or other suitable material (including metal or hard plastic alloys and the like) such as which can exhibit any thickness not limited to a dimensional range of 0.001″ to 0.010″ (typically 0.004″). The shim stock body exhibits an arcuate profile 12 generally matching the profile of a selected ear associated with the firearm receiver and further includes a flat base surface 14, this further generally matching the corresponding profile of the base surface of the lower receiver where the ears (see as subsequently depicted at 26 and 28 in FIG. 1) is integrally formed therewith and which, upon installing the shim 10 in a manner best depicted in FIGS. 6C et seq., seats the thin shim stock body in a secure and non-rotating fashion upon the inner seating surface of the ear prior and during interposed insertion and installation of the upper receiver tubular mounting projection.

The shim includes an inner aperture (see inner perimeter wall 16) which matches the corresponding aligned apertures associated with the upper and lower receiver pivot pin mounts. The outer profile of the shim 10 further exhibits angled corner locations 18 and 20, these aligning and seating with corresponding edge profiles of the lower receiver ear surface (see again FIG. 6C) to securely mount the shim body in place, as well as to prevent rotation or any other undesirable movement of the shim body.

Upon installation, the shim 10 removes the existence of any excess tolerance or play between the upper and lower receivers, thereby creating a tighter fit of the two parts. It is further noted that the shim, when installed, will not hinder the operation of the firearm at any time, with the receivers further being broken open for responding to any desired remedial action without changing the process as to how the operator manipulates the firearm, thus allowing the shim to be installed in any firearm or for any operator to use the firearm (rifle) with the shim installed without any additional training.

Having provided a brief description of the structure and manner of installation of the uniquely configured shim, a brief description of the supporting drawings is provided with FIG. 1 being a close up exploded view of a forward pivot pin arrangement established between upper 22 and lower 24 receivers of an AR15 type firearm and including spaced apart ears 26 and 28 associated with the lower receiver and between which seats a tubular shaped and downwardly extending lug protrusion 30 associated with the upper receiver. A crosswise plurality of aligning apertures is depicted at 27 and 29 in inner perimeter defining fashion for each of ears 26 and 28, in combination with a further inner aperture defining closed perimeter 31 (see again FIG. 1) and which, upon alignment with the protrusion 30, enables a widthwise displacing pin to engage the upper 22 and lower 24 receivers together. A widthwise projecting pin 32 extends from selected ear 28, typically in a fully laterally retracted position as depicted in FIG. 1, such that unobstructed clearance is provided for locating the central protrusion 30 and one or more desired shim elements 10.

FIG. 2 complements FIG. 1 and is a further separated view of the upper and lower receivers. FIG. 3 is a perspective view of a separated lower receiver and depicting both the forward pivot pin construction previously depicted in FIG. 1 in combination with rearward spaced take down pin 34 associated with the lower receiver 24 and which engages a corresponding lateral extending profile of the upper receiver 22 (not shown in this view) upon seating the cylindrical rear end of the upper receiver barrel (also not shown) within a receiving/seating profile 36 associated with the lower receiver 24 and extending upwardly approximate its handle or stock 38.

FIGS. 4A and 4B are successive disassembly views of the upper and lower AR15 receivers and depicting the unique shim stock design of the present invention, with FIG. 5 again illustrating the unique shim shape, such as exhibiting a 0.004″ thickness, and which generally matches the profile of a selected ear associated with the lower receiver take down pin 32 depicted in FIG. 6A. FIGS. 6A-6C illustrate successive assembly steps for positioning the unique shim stock portion 10 on selected lower receiver ear concurrent with assembling the upper receiver tubular potion such that the shim stock is sandwiched therebetween, with FIGS. 6C and 6D again being illustrative of progressive assembly steps taken from the explanation provided above.

FIG. 6B is an alternate depiction of a kit of shims depicted in one exemplary plurality at 10, 10′ and 10″, and which is capable of being provided in any desired stacked fashion as an alternate to using a single shim 10 as previously described. The variant of FIG. 6B is useful in particular in situations where an excessive amount of lateral side-to-side slop or play results from any gross degree of excess tolerance, and which in particular can result when upper and lower receivers of a given weapon type are interchanged.

FIGS. 6C-6F depict further progressive assembly steps (also applicable to the alternate kit arrangement of FIG. 6B) in which the pivot pin 32 is initially fully retracted to an initially located and pre-installed position (FIGS. 6D-6E), following which the pin 32 is progressively displaced inwardly (FIG. 6F) across the widthwise extending and aligned components of the ears 26 and 28 of the upper 22 receiver and the interposed lug protrusion 30 of the lower 24 receiver, with the shim stock 10 previously installed in place between the selected inner facing side of an ear 26 and 28 (such as depicted in FIG. 6C in which the flat base surface 14 adheres against a flat inner edge 40) and the lateral exterior edge of the lug protrusion 30. In this fashion, the shims (either singularly applied 10 or in plural fashion 10, 10′, 10″) are better retained in immovable/non-rotating fashion at the mounting interface during installation or takedown.

Having described my invention, other and additional preferred embodiments will become apparent to those skilled in the art to which it pertains, and without deviating from the scope of the appended claims.