Firearm upper receiver positioning mechanism

A firearm having a lower receiver including a takedown pin through hole and an upper receiver configured to receive the lower receiver. The upper receiver including a rear lug and the rear lug including a bore and a screw disposed in the bore. A takedown pin having a cam surface such that the upper receiver is drawn to the lower receiver as the takedown pin is inserted in the takedown pin through hole and the bore of the rear lug.

FIELD OF DISCLOSURE

The present disclosure relates generally to firearms, and more particularly, to an automatic rifle with an upper receiver positioning mechanism.

BACKGROUND

Automatic or semi-automatic rifles typically include an upper receiver and a lower receiver. The upper receiver can support a number of rifle components, for example, a barrel and sights. The lower receiver may also support and/or house other components, such as an ammunition magazine, a grip, and a trigger mechanism. The upper receiver may be pivotally attached to the lower receiver using a pivot pin. A user of the firearm may access internal rifle components by pivoting the upper receiver away from the lower receiver about the pivot pin. Access to internal rifle components may be desirable for a number of reasons, such as cleaning and maintenance. The upper receiver is typically secured to the lower receiver using a takedown pin. The takedown pin may be located opposite of the pivot pin and proximate to the aft end of the receivers. When installed, the takedown pin secures the upper receiver to the lower receiver enabling operation of the rifle.

SUMMARY

One example embodiment provides a firearm including: a lower receiver including a takedown pin through hole; an upper receiver configured to receive the lower receiver and including a rear lug, the rear lug including a bore and a screw disposed in the bore; and a takedown pin including a cam surface, wherein the upper receiver is drawn to the lower receiver as the takedown pin is inserted in the takedown pin through hole and the bore of the rear lug. In some cases, the firearm includes a threaded insert installed in a wall of the rear lug, wherein the screw is inserted into the threaded insert and a distal end of the screw extends into in the bore of the rear lug. In some such cases, the screw is installed perpendicular to a longitudinal axis of the firearm. In some cases, the screw is installed perpendicular to a transverse axis of the firearm. In other such cases, the screw is installed through a bottom surface of the rear lug. In some other such cases, the screw can be adjusted to extend or contract an effective diameter of the bore. In other cases, the cam surface includes an upwardly sloped surface configured to receive a distal end of the screw disposed in the bore of the rear lug of the upper receiver and to draw the upper receiver to the lower receiver to reduce a gap there between as the takedown pin is inserted In some such cases, the takedown pin a downwardly sloped surface, the downwardly sloped surface progressing in a direction from an insertable end to a head of the takedown pin such that, when the takedown pin is inserted the screw contacts the downwardly sloped surface to provide a lateral force that biases the upper receiver against the lower receiver to reduce horizontal movement of the upper receiver in relation to the lower receiver along a transverse axis of the firearm. In some instances, the screw is a dog-point set screw. In other instances, the upper receiver and lower receiver define a gap there between when the takedown pin is fully inserted, wherein a size of the gap is shortened or lengthened by adjusting a position of a distal end of the screw within the bore of the rear lug. In other cases, at least a portion of the cam surface is sloped downwardly progressing in a direction from the insertable end to the head. In some other cases, wherein the takedown pin includes a substantially planar first surface, a second surface and a third surface, wherein: the first surface is located at a distance from a centerline of the takedown pin, the distance being less than a largest radius of a body of the takedown pin; the second surface is a tapered contoured surface adjacent the first substantially planar surface, the second surface tapered upwardly as it extends from the first substantially planar surface towards a head of the takedown pin; and the third surface having a first end and a second end, the first end transitioning from the second surface toward the head of the takedown pin, wherein at least a portion of the third surface is sloped downwardly from the first end to the second end. In other instances, when the takedown pin is installed, the cam surface is to face downward towards the lower receiver. In some other instances, the cam surface is positioned about 90 degrees around the takedown pin from to a longitudinal groove in the takedown pin, the longitudinal groove constructed and arranged for receiving a detent plunger. In some such cases, the longitudinal groove includes a depression in each end of the groove, each depression positioned and sized to receive the detent plunger in an extended position. In yet other cases, the cam surface is formed in a floor of a longitudinal groove for receiving a detent plunger. In some such cases, the longitudinal groove includes a depression in each end of the groove, each depression positioned and sized to receive the detent plunger in an extended position. In some cases, the upper receiver further comprises: a forward lug disposed on the upper receiver, wherein the forward lug includes a bore and an adjustable bushing disposed in the bore; and a pivot pin installed in the lower receiver and the bushing, wherein the upper receiver is pivotally attached to the lower receiver. In other instances, the rear lug further includes a threaded hole located within a bottom surface of the rear lug and perpendicular to the bore of the rear lug. In some such instances, the firearm includes a lock nut disposed on the screw, wherein the lock nut is to be tightened against the rear lug to secure the screw within the threaded hole of the rear lug. In some other such instances, the lock nut is a jam nut. In other cases, the firearm includes a self-locking element disposed on one or more threads of the screw, wherein the self-locking element is to engage one or more threads of a threaded hole of the rear lug to secure the screw in the threaded hole of the rear lug. In some such cases, the self-locking element is a nylon patch.

According to another example embodiment, a firearm includes a lower receiver including two mounting brackets, each mounting bracket defining a through hole and having an interior and an exterior surface; an upper receiver configured to receive the lower receiver and including a forward lug, the forward lug including a bore and an adjustable bushing disposed in the bore; and a pivot pin installed in the forward lug and the two mounting brackets, wherein the upper receiver is pivotally attached to the lower receiver. In some cases, the bushing can be horizontally adjusted in the bore of the forward lug, such that, when the pivot pin is installed, the interior surface of each mounting bracket is in contact with either the adjustable bushing or the forward lug and prevents side-to-side movement of the upper receiver in relation to the lower receiver. In other cases, the adjustable bushing includes a head, such that, the head provides a bearing surface to distribute an applied force transmitted from the upper receiver to the lower receiver. In some such cases, the head of the adjustable bushing includes one or more cut outs for receiving a tool. In other cases, the upper receiver further comprises: a rear lug disposed on the upper receiver, wherein the rear lug includes a bore and a screw disposed in the bore; and a takedown pin having a cam surface, wherein the takedown pin is installed in the lower receiver and the bore of the rear lug, such that, the cam surface contacts the screw causing the upper receiver to make contact with the lower receiver.

According to another example embodiment, a firearm includes a lower receiver including a takedown pin through hole; an upper receiver configured to receive the lower receiver and including a rear lug and a forward lug, wherein: the rear lug includes a bore, a threaded portion passing through the rear lug into the bore, and a screw, wherein the screw is installed in the threaded portion and disposed in the bore; and the forward lug including a bore and a bushing, wherein the bushing is installed in the bore; a takedown pin having a cam surface, wherein the upper receiver is drawn to the lower receiver as the takedown pin is inserted into the takedown pin through hole and the bore of the rear lug; and a pivot pin installed in the lower receiver and the bushing, wherein the upper receiver is pivotally attached to the lower receiver.

DETAILED DESCRIPTION

General Overview

As previously discussed, automatic rifles may include an upper and lower receiver that are attached and secured together using a pivot pin and takedown pin. Dimensional tolerances of rifle components, however, affect how automatic rifles are constructed and assembled. For efficiency and ease of assembly, component tolerances may be larger than ideal, resulting in both vertical and horizontal play between the upper and lower receivers when the rifle is fully assembled. This movement may occur about the pivot pin, takedown pin or both during rifle firing. Movement about the pivot pin, for example, may occur along a transverse axis of the rifle in a horizontal direction. The upper receiver may move horizontally in relation to the lower receiver because a forward lug of the upper receiver may not fully fill the space between the brackets on the lower receiver when the pivot pin is installed. As a result, a gap may exist between these components. This gap may allow the upper receiver to move in a horizontal direction in relation to the lower receiver. This movement may be, for example, approximately 0.010 to 0.020 inches.

Movement about the takedown pin may occur in the horizontal and vertical directions. The upper receiver may move horizontally because, due to necessary manufacturing tolerances, a rear lug of the upper receiver may not contact both adjoining interior surfaces of the lower receiver when the takedown pin is installed. As a result, the upper receiver may move horizontally in relation to the lower receiver by a distance approximately equal to the gap between the rear lug and the interior surfaces of the mounting brackets in the lower receiver. When fully assembled, the upper receiver may also move vertically in relation to the lower receiver because the mating surfaces of the upper and lower receivers may not be biased against one another. This may be the result of a takedown pin that has an outer diameter that is smaller than the inner diameter of the bore through the rear lug, the bore through the bracket, or both. As a result, there is some play around the takedown pin when it is installed resulting in a gap along the longitudinal interface between the upper and lower receivers. This gap may permit the upper receiver to move vertically up and down in relation to the lower receiver during rifle firing. This gap may be, for example, approximately 0.010 to 0.020 inches. Thus, more than one gap may be present due to the necessary tolerances in the upper and lower receivers as well as the pivot pin and takedown pin. No matter which gap is present, any play between the upper receiver and lower receiver may diminish the accuracy of the rifle because the barrel and projectile may move in conjunction with the upper receiver in response to recoil forces generated during rifle firing. As the manufacturing tolerances cannot be reduced for mass produced firearms without a greatly increased scrap rate, the resulting gaps are necessary and common, and these gaps and resulting movement have become expected by firearm users.

In accordance with a set of embodiments, an upper receiver positioning mechanism for an automatic rifle is disclosed. In some embodiments, the upper receiver positioning mechanism can adjust the upper receiver to reduce or otherwise eliminate vertical, horizontal, and/or rolling motion of the upper receiver about the takedown pin. In other embodiments, the upper receiver positioning mechanism can adjust the forward end of the upper receiver to reduce or eliminate any side-to-side movement of the upper receiver about the pivot pin. In yet further embodiments, the upper receiver positioning mechanism may constrain the movement of the upper receiver about both the pivot pin and takedown pin.

According to an embodiment, the upper receiver positioning mechanism may include a takedown pin positioning mechanism. The takedown pin positioning mechanism may comprise a lug including a bore therethrough, a screw adjustable in the bore, and a takedown pin. The lug may be in the upper or lower receiver. In an example case, the adjustable screw may be installed in a rear lug of the upper receiver. In this case, the screw may be inserted into a bottom surface of the rear lug, such that, an end of the screw can be advanced into the bore of the rear lug. The lug may include a threaded insert for receiving the screw. In other embodiments, the lug itself may be threaded to receive the screw. The screw can be positioned so that it protrudes into the bore of the lug to interface with a cam surface of the takedown pin when the takedown pin is inserted through the bore. Advancement of the end of the screw into the bore can reduce the effective diameter of the bore. In this embodiment, the takedown pin may include three surfaces: (1) an installation surface, (2) a cam surface and (3) an adjustment surface. The installation surface may reduce the effective diameter of the takedown pin to enable quick and efficient insertion of the takedown pin by providing ample clearance and less lateral resistance between the leading portion of the pin and the screw. As the takedown pin is pushed further through the lug bore, the screw may contact the cam surface. In this case, the cam surface may be tapered to guide the screw along the pin to prevent binding or damage to the screw, pin or combination thereof. The cam surface can interface with the screw and the resulting cam action provides a vertical force causing the upper receiver to move vertically. In some embodiments, this vertical movement of the upper receiver is downward, pulling the upper receiver into the lower receiver. When the takedown pin is fully installed, the screw may contact the adjustment surface. The adjustment surface may provide a bearing surface for the screw to maintain the upper receiver in the adjusted position. In some instances, the adjustment surface may be sloped with respect to the axis of the takedown pin so that the upper receiver is biased against an interior surface of the lower receiver in a horizontal direction.

In an exemplary embodiment, the positioning of the upper receiver may be adjusted to eliminate movement of the upper receiver in relation to lower receiver (as previously described) by installing the takedown pin having a cam surface. As the takedown pin passes through the lower receiver and into the bore of the rear lug of the upper receiver, the screw may contact the one or more of the cam surfaces. With the screw properly adjusted and the takedown pin fully installed, the downward force applied to the exposed end of the screw from contact with the cam surface causes the screw and the rear lug to be displaced downward until the upper receiver contacts the lower receiver.

In one set of embodiments, the upper receiver positioning mechanism may include a pivot pin positioning mechanism. The pivot pin positioning mechanism can include an adjustable bushing. In this example case, the bushing can be externally threaded for installation into a threaded bore of a forward lug of the upper receiver. The bushing may include a head that provides a bearing surface for transferring the applied load from the upper receiver to the lower receiver when the bushing bridges a gap between the two receivers.

In this embodiment, the gap between the forward lug of the upper receiver and the walls of the lower receiver may be reduced or eliminated using the bushing. In this case, the bushing may be installed into the bore of the forward lug, such that, when the pivot pin is installed into the upper and lower receivers, the bushing may contact the lower receiver. With the bushing bridging or filling the horizontal gap between the two receivers, the upper receiver can be prevented from moving in the horizontal direction.

As will be appreciated in light of this disclosure, some embodiments may realize benefits and advantages as compared to existing approaches. For instance, the embodiments described herein may improve the accuracy of the rifle, because the relative motion between the upper receiver and the lower receiver is reduced or eliminated. The reduction of the gap between the upper and lower receivers can also provide a more solid feel to the firearm. The increased level of contact between the upper and lower receivers can prevent any motion of the upper receiver caused by recoil forces generated during rifle firing, and thus improve overall rifle accuracy. In other instances, the embodiments described herein may allow manufacturers of automatic rifles to produce rifles more efficiently and easily without the use of additional or special tooling while maintaining rifle accuracy. Manufacturers, for example, can mass produce rifles as currently done in the industry and then install the mechanisms described herein, to fine tune the installation of rifle components. With significant variation in sizes and tolerances of rifle components, these mechanisms may enable a rifle manufacturer to quickly and easily adjust the rifle assembly without undue delay. The embodiments described herein can also be implemented subsequently during the service life of the rifle. The takedown pin mechanism, for example, can enable users to subsequently adjust the position of the upper receiver during the life of the rifle to compensate for wear of components over time. In this instance, a user may simply tighten or loosen the screw to re-position the upper receiver. Similar adjustments may be accomplished at the forward pivot pin mechanism to reduce or eliminate relative motion between the upper receiver and the lower receiver in the horizontal direction. In this case, the bushing may either be threaded into or out of the forward lug, as needed, to allow for pivoting while maintaining contact between the bushing and the brackets of the lower receiver.

Rifle Structure

FIG. 1is a perspective view of one embodiment of an automatic rifle100having a lower receiver104and an upper receiver108.FIG. 2is a perspective cut-away view of the automatic rifle100with an upper receiver108rotated about a pivot pin112, in accordance with an embodiment of the present disclosure. The lower receiver104may be positioned beneath and support the upper receiver108. The lower receiver104may include other rifle components, for example, a grip or trigger mechanism. Other components of the rifle100, such as a barrel and sights, can be supported or housed by the upper receiver108. The upper receiver108may be pivotally attached to a lower receiver104using a pivot pin112. The pivot pin112pivotally connects the forward ends of upper receiver108and lower receiver104. As can be seen inFIG. 2, when rotated or pivoted about the pivot pin112, the upper receiver108can be separated from the lower receiver104to facilitate cleaning and maintenance of the rifle100without completely separating the two receivers from one another. To fix or secure the upper receiver108to the lower receiver104, a takedown pin116may be installed. The takedown pin116maintains the position of the upper receiver108in relation to the lower receiver104when the pin116is installed into the aft end of the receivers. With the takedown pin116installed, the upper receiver108and the lower receiver104may define a gap120(as shown) along mating surfaces132of the lower receiver104. The gap120may be caused by component tolerances that are necessary for manufacturing the rifle100or through the wear of individual rifle components over time.

FIG. 3is a perspective view of an embodiment of a lower receiver104illustrating forward mounting brackets204and aft mounting brackets208. The forward mounting brackets204receive and support the pivot pin112. In general, the forward mounting brackets204may have any shape and/or be located at any position suitable for receiving the pivot pin112and the upper receiver108. In an example case, the forward mounting brackets204can be positioned at the forward end of the lower receiver104and may extend from a forward surface of the lower receiver104in a direction along the longitudinal axis124(FIG. 1). The forward mounting brackets204may also be parallel with one another along the transverse axis128(FIG. 1). The forward mounting brackets204can also include a bore for receiving the pivot pin112. While the forward mounting brackets204may support the pivot pin112, the aft mounting brackets208can support the takedown pin116. To this end, the aft mounting brackets208may be any size or shape suitable for receiving the takedown pin116and the upper receiver108. In this case, the aft mounting brackets208can be integrated into the aft end of the lower receiver104and include a bore for receiving the takedown pin116. To pivotally attach the upper receiver108to the lower receiver104, the upper receiver108can be configured to receive the pivot pin112and takedown pin116.

FIG. 4is a perspective view of an embodiment of an upper receiver including a forward lug304and a rear lug308. The upper receiver108may be configured such that the forward lug304and rear lug308are received by forward mounting brackets204and aft mounting brackets208(respectively). The forward lug304may connect the upper receiver108to the lower receiver via pivot pin112to enable the upper receiver108to pivot or rotate about the pivot pin112. In an example case, the forward lug304may be located at the forward end of the upper receiver108and may extend downward from a bottom surface of upper receiver108. The forward lug304may include a bore306in the direction of the transverse axis128to receive the pivot pin112. The bore306may be threaded for receiving a bushing, as will be described further herein. While the forward lug304may receive the pivot pin112, the rear lug308can receive the takedown pin116. The rear lug308may connect the upper receiver108to the takedown pin116to secure or otherwise fix the upper receiver108to the lower receiver104. In this example case, the rear lug308can be located proximate to the aft end of the upper receiver108and may extend downward from the bottom surface of the upper receiver108. The rear lug308may include a bore310having an axis in the direction of the transverse axis128to receive the takedown pin116to facilitate assembly of rifle100.

For ease of rifle assembly, the components of the rifle100may be manufactured with machining tolerances that enable efficient rifle assembly without an excessive scrap rate and without the use of additional or special tooling. As previously described, these tolerances may allow the upper receiver108to be displaced vertically in relation to the lower receiver or move horizontally in relation to the lower receiver or both during firing of rifle100. As a result, the movement of the upper receiver108may cause inaccuracies during rifle firing. To limit or otherwise eliminate movement of the upper receiver108and thus improve the accuracy of the rifle100, the devices and mechanisms disclosed herein can securely and tightly attach the upper receiver108to the lower receiver104.

Takedown Pin Positioning Mechanism Structure and Operation

As previously described, during firing of automatic rifle100the upper receiver108may be displaced in relation to the lower receiver104due to recoil forces. This displacement may result in the upper receiver108moving in a vertical and/or horizontal direction in relation to the lower receiver104. To reduce or eliminate this movement, a takedown pin positioning mechanism is provided that draws down the upper receiver108onto the lower receiver104and thus reduces or eliminates the gap120defined by the receivers. With the gap120eliminated, the upper receiver108can maintain its position in relation to the lower receiver104and movement between the two receivers is reduced or eliminated. In some embodiments, the gap120may be eliminated so that the upper and lower receivers are in frictional contact with one another at portions of, or the entire region of, the previous position of the gap. In other embodiments, the gap120is reduced so that the freedom of movement between the upper and lower receivers is reduced. For instance, the positioning mechanism can reduce the gap120by 50%, 75% or greater than 90% at one or more points along the interface between the receivers. Similarly, when compared to the same rifle without the positioning mechanism, the gap120may be decreased by approximately 0.010 to 0.020 inches.

FIG. 5is a cross-sectional view of automatic rifle100illustrating a takedown pin positioning mechanism400, in accordance with an example embodiment. The positioning mechanism400may include a threaded insert404, screw408, and takedown pin412. As can be seen, the rear lug308of the upper receiver108includes a hole for receiving the threaded insert404. This hole may be located perpendicular to the bore310for receiving the takedown pin412and may be located anywhere in the bottom surface of the rear lug308, such that, the threaded insert404may be installed.

When installed in the rear lug308, the threaded insert404can provide a threaded hole for receiving a fastener (e.g., screw408as will be described). The threaded insert404may include external and internal threads for engaging the rear lug308and the fastener (respectively). Accordingly, the rear lug308itself may be internally threaded to receive the insert404or, in some cases, receive the screw408(as described below). The threaded insert404can be any type of insert, such as a helical insert or screw-thread insert, and may be comprised of, for example, steel. An example of a helical insert is a HELI-COIL® threaded insert. Other types of inserts may include a press-fit insert or a threaded bushing. The threaded insert404can be manufactured from any material that is capable of withstanding the forces generated during use and firing of the rifle100, for example, metals such as carbon steel and aluminum, polymers or graphite. The threaded insert404may be installed into the rear lug308using a locking feature, for example, a locking compound, locking pellet, or a flattened thread.

In other embodiments the takedown pin positioning mechanism400may not include a threaded insert404. In these cases, the rear lug308may include a threaded hole to receive the screw408. To maintain the screw408within the threaded hole of the rear lug308, the takedown pin positioning mechanism400may also include a retention device. The retention device may be any device capable of retaining the screw408in an installed position, such as, a lock nut or self-locking element. The lock nut in some instances may be a jam nut having a low profile. A jam nut may lock the screw408in position when the jam nut is disposed onto the threads of the screw408and tightened against the surface of the rear lug308. Jam nuts may be preferred in some instances, where vibrations may cause the fastened joint to loosen or separate. Similarly, self-locking elements may also prevent the screw408from loosening or unthreading from the rear lug308due to vibrations. A self-locking element may be installed onto one or more threads of the screw408, such that, when installing the screw408the element engages a number of threads of the threaded hole in the rear lug308. As a result of the engagement between the self-locking element and the threads of the threaded hole, the necessary force to unthread or loosen the screw408may increase. Some examples of self-locking elements may include a nylon pellet, a nylon strip, or a nylon patch. No matter whether a threaded insert404is installed in the rear lug308or not, the rear lug is to receive a screw408.

Screw408may be disposed within the rear lug308. When installed, the screw408may interface or engage the takedown pin412to position the upper receiver108in contact with the lower receiver104(as will be discussed in further detail). In this case, the screw408can be any type or size screw that can be installed into the threaded insert404and configured to engage the takedown pin412. In many cases, the screw408is inserted so that none of the screw protrudes from the bottom of insert404. This can help, for example, to minimize interference between the rear lug308and the lower receiver104. In an example case, screw408may be a headless screw such as a dog-point set screw. A dog-point set screw may be preferred in some embodiments, because the dog-point provides a flat surface for interfacing with the takedown pin412. In many embodiments, screw408provides an axial force to draw the upper receiver108towards the lower receiver104and a larger surface area in contact with the takedown pin412can improve this interface. In other cases, the screw408may be flat, plain cup, or half-dog point set screw. The screw408may also be a different type, for example, hex or Allen head cap screw. As shown, screw408is made of carbon steel and is able to withstand the applied loading and recoil forces generated during rifle firing. In a more general sense, the screw408can be any type of fastener that can be installed in the rear lug308and engage the takedown pin412to draw the upper receiver108onto the lower receiver104.

The screw408may interface with takedown pin412to position the upper receiver108onto contact with the lower receiver104. When installed the takedown pin412may secure the upper receiver108to the lower receiver104. In this example case, the takedown pin412may include a cam surface that interfaces with screw408(as will be discussed in further detail). The takedown pin412may be of any length suitable for installation into the receivers104and108. To this end, note that the length of the takedown pin412should be sufficient to allow the pin412to be properly supported by the aft mounting brackets208of the lower receiver104and permit proper function of the takedown pin detent mechanism (not shown). In this case, the takedown pin412may have a length of approximately 1.188 inches. The takedown pin412may be manufactured from a variety of materials, for example hardened steel, that are capable of withstanding the forces applied to the pin412during firing of the rifle100.

FIGS. 6A-6Dillustrate one embodiment of the takedown pin412including a cam surface524, in accordance with the present disclosure. In an example case, the takedown pin412can be a cylinder-shaped pin having a head504, a shank508, a groove512, and a cam surface524. In other cases, the takedown pin412may have a conical taper, the leading end having a smaller diameter than the trailing end, as inserted into the rifle. The head504of the takedown pin412may provide a surface for rifle users to apply a force against when inserting the takedown pin412into the lower receiver104and upper receiver108. The head504may also include an indicator to instruct a user how to orientate the takedown pin412prior to pin installation. The indicator may ensure that the user installs the takedown pin412such that the screw408can be aligned with the cam surface524. The indicator may be any visual cue that alerts the user as to how to install the takedown pin412with the cam surface524aligned with the screw408. In an example case, the indicator may be a set of arrows. One arrow may be located on the head504and the other on the lower receiver104. When the arrows are pointing at one another, then the takedown pin412can be properly installed into the lower receiver104and rear lug308of the upper receiver108. The head504may be any size or shape for ease of removal and installation of the takedown pin412from rifle100. In this case, the head504can be round having a diameter of 0.437 inches. In other cases, the head504may be a square or hexagon and the surface may be flat or rounded. No matter the style or shape, the head504may be attached to the shank508of the takedown pin412.

Attached to the underside of the head504may be a body or shank508. When fully inserted, the shank508of the takedown pin412maintains the upper receiver108in contact with the lower receiver104. The shank508may be any size that permits installation into the bores of the aft mounting brackets208of the lower receiver104and the rear lug308of the upper receiver108. In this example case, the shank508may be a round cylinder having a diameter of approximately 0.275 inches. As can be seen, the shank508may also include a groove512and one or more surfaces to facilitate the installation of the takedown pin412(e.g., an installation surface520, cam surface524, and adjustment surface528).

The shank508may also include groove512for receiving a detent plunger. The groove512interfaces with the detent plunger during installation and removal of the takedown pin412. The detent plunger can help to ensure that the takedown pin412is properly oriented and does not fall out when the rifle is dismantled. The groove512may be located along the surface of the shank508such that the groove512can interface with a plunger of a detent mechanism for the rifle100. As can be seen inFIG. 6A, in this example case the groove512may be located parallel to a centerline of the takedown pin412and positioned about 90 degrees away from the cam surface524.

The shank508may include an installation surface520. While installing the takedown pin412, the installation surface520can provide clearance and less lateral resistance between the screw408and the pin412, as the pin412travels through the bore310of the rear lug308. Without this additional clearance, protruding screw408may prevent installation of the takedown pin412or increase the force necessary to install the pin412. This surface can also help to orient the takedown pin412, as the installation surface should be aligned with the screw408in order for it to be inserted into the rear lug308. As can be seen, the installation surface520may be generally flat having a length and width that allows the takedown pin412to pass over the screw408with little or no lateral resistance. In this case, the installation surface520is approximately 0.500 inch in length having a chamfered surface at one end and a tapered surface at the other end extending into the cam surface524.

The shank508can also include a cam surface524that is adjacent to the installation surface520. In an example embodiment, the cam surface524is located between the installation surface520and the adjustment surface528. During installation of the takedown pin412, the cam surface524contacts the screw408to produce a camming action in which the upper receiver108is drawn to the lower receiver104to reduce a gap120therebetween during installation of the takedown pin412into firearm100, as will be described further herein. In addition, the cam surface524may guide the end of the screw408onto the adjustment surface528. In many embodiments, the cam surface524can be any size or shape capable of contacting the screw408and converting the lateral force applied to the takedown pin412into a vertical force pulling the two receivers toward each other. The cam surface524may also enable the takedown pin412to contact the end of the screw408and permit further installation of takedown pin412. The cam surface524, for example, may be a curved or planar surface that is sloped, or otherwise contoured depending on the application. In this case the cam surface524can comprise one, two, three or more adjoining surfaces of varying slopes. For example, the slopes of adjoining surfaces, from proximal to distal ends, may change from shallow to steep to shallow. The transition may be continuous or may be in steps. For example, the cam surface524, in some embodiments, includes a first curved portion525of, for example, a 0.125 inch radius. From this radius, the cam surface524further includes a portion526that slopes upwardly along an axis532of the takedown pin412as shown inFIG. 6C. This upwardly sloped portion526is followed by a second curved portion527, for example a 0.030 inch radius, to join or otherwise provide a transition to the adjustment surface528. In more detail, as the takedown pin412is pushed through rear lug308, the greatest point of resistance, and greatest resulting vertical force, may be when the highest or otherwise uppermost portion of the cam surface524(e.g., curved portion527) passes the distal end420of screw408. It is at this point that the two receivers are most tightly drawn together. As the takedown pin412advances past this point, the slight downward slope of the adjustment surface528along axis536means that the vertical force pulling the two receivers together is slightly reduced or otherwise relaxed, possibly resulting in an expansion of gap120between the upper and lower receivers when compared to the size of gap120when screw408was in contact with the cam surface524. In other embodiments, the adjoining upper and lower receivers may exhibit enough elasticity that they can be compressed together at the uppermost portion of cam surface524and still remain in contact after a reduction in compression force as the screw408passes along the downwardly sloping adjustment surface528. The final position of rest on the adjustment surface528can be very stable because vibrations are unlikely to back out takedown pin412as the horizontal force required to do so will be inadequate to move the cam surface524past screw408.

The cam surface524may guide the screw408to its final location along the adjustment surface528adjacent thereto. The adjustment surface528can provide a bearing surface to maintain the upper receiver108in position relative to the lower receiver104. In addition, the adjustment surface528, in some embodiments, can be a slight sloped surface to keep a horizontal force on takedown pin412that prevents the takedown pin412from backing out during rifle firing. In addition, surface528can also laterally position the upper receiver108and lower receiver104relative to one another to prevent horizontal movement of the receivers104and108relative to one another along the transverse axis128, as described further herein. The adjustment surface528, for example, may be flat or otherwise planar surface that is sloped, and/or contoured depending on the application. In this case, the adjustment surface528may be sloped, for example, at 0.25 degrees from the centerline of the takedown pin412in a downward direction along axis536as shown inFIG. 6D. In many embodiments, the adjustment surface528may be capable of maintaining contact with the screw408and re-positioning the upper receiver108horizontally relative to the lower receiver104. In such embodiments, the upper receiver108can be biased laterally against a surface of the lower receiver104to prevent or otherwise reduce movement of the upper receiver108relative to the lower receiver104. The upper receiver108can be biased in a direction along the transverse axis128of the firearm100. Thus, with the two receivers in multiple points of contact with one another, the receivers may no longer move in either the vertical or horizontal directions relative to one another during rifle firing.

The surfaces of the takedown pin412that interface with the distal end of the screw408or otherwise facilitate the installation of pin412(e.g., an installation surface520, cam surface524, and adjustment surface528) can be machined into the cylindrical body of the takedown pin412to produce, for instance, flat, tapered or curved surfaces. The surfaces520,524, and528may be located anywhere along the circumference of the shank508, as long as the end of screw408can contact the cam surface524and adjustment surface528. As can be seen, these surfaces520,524, and528, in an example embodiment, are located 90 degrees from groove512that receives the detent plunger. Together the surfaces520,524and528can be any suitable size or length capable of interfacing with the screw408. The combined length of these surfaces, for example, can be of a length, such that, when the takedown pin412is fully installed, the adjustment surface528is in contact with the screw408. In addition, the width of the surfaces520,524, and528can be any width capable of receiving part or all of the screw408. In a more general sense, the surfaces520,524, and528can be any size or shape, such that: (1) the takedown pin412can be physically installed into the bore310of the rear lug308with screw408disposed in the bore; and (2) when the takedown pin412is installed, the screw408may contact the cam surface524to re-position the upper receiver108.

FIGS. 7A-7Dillustrate installing a takedown pin412to reduce or eliminate the gap120between the upper receiver108and lower receiver104, in accordance with the present disclosure. As can be seen in the cutaway view ofFIG. 7A, the takedown pin412is in a retracted or unlocked position. In the retracted or unlocked position, the upper receiver108can be extended or pivoted away from the lower receiver104because the takedown pin412is not engaged in the rear lug308of the upper receiver108. In some cases, the takedown pin412may be entirely removed from the lower receiver104. Or, as can be seen, the takedown pin412can be partially installed into one of the aft mounting brackets208. In this position the takedown pin412may be prevented from being completely removed from the lower receiver104by a detent plunger (not shown). A gap120may also be present between the lower receiver104and upper receiver108. The gap120may be present when the upper receiver108and lower receiver104do not make contact with one another. As a result, during rifle firing the upper receiver108may move (as previously described). To address this issue, the rear lug308of the upper receiver108may include an adjustable screw408as shown. As can be seen, the distal end420of the screw408may protrude into the bore310of the rear lug308.

FIG. 7Billustrates the screw408in contact with the installation surface520of the takedown pin412. As the assembler of the rifle100begins to install the takedown pin412, the assembler may apply an axial force to the head504of the takedown pin412. The force may be applied to the takedown pin412using a finger, thumb, tool, or any combination thereof. As a result of the applied force, the takedown pin412may move into the bore310of the rear lug308of the upper receiver108. In this position, the takedown pin412is also partially inserted into the opposing aft mounting bracket208of the lower receiver104(as shown). When the takedown pin412begins to move into the opposing aft mounting bracket208, the distal end420of screw408is adjacent to, but may or may not contact the installation surface520of the pin412. As can be seen, the gap120may be reduced, but not eliminated as a result of the screw408contacting the installation surface520of the takedown pin412or the takedown pin412contacting an inner surface of the opposing aft mounting bracket208(or both). The gap120may be further reduced or eliminated when the screw408contacts the cam surface524.

FIG. 7Cis a cross-sectional view illustrating the screw408contacting the cam surface524of the takedown pin412and thus reducing the gap120. As can be seen, the takedown pin412is positioned further into the aft mounting brackets208of the lower receiver104, but is not yet completely installed. As the screw408contacts the cam surface524, a downward force is applied to the screw408causing the upper receiver108to move downward vertically. In this example case, the cam surface524may include curved portions, such as a 0.125 and 0.030 radius (as previously described). These curved portions may be, for example, at the entry and exit of the cam surface524. The radii may create a domed-shape surface, such that, when the distal end420of the screw408contacts the raised portion of the curved surface the maximum amount of vertical force may be applied to the upper receiver108. In response to this contact, the screw408and upper receiver108may be drawn down towards the lower receiver104. It is at this point that the two receivers are the most tightly drawn together. As can be seen, the upper receiver108may be in two points of contact,610A and610B, with the lower receiver104. The screw408and upper receiver108move downward because the takedown pin412is constrained from moving upward by the aft mounting brackets208. As a result of the downward movement of the upper receiver108, the gap120can be reduced or eliminated. With the gap120reduced or eliminated, the takedown pin412may be completely or fully installed into the rifle100.

FIG. 7Dillustrates the screw408in contact with the adjustment surface528of the takedown pin412to maintain the upper receiver108in a fixed position relative to lower receiver104. As can be seen, the takedown pin412is completely installed into the rifle100and thus the takedown pin412is positioned within both aft mounting brackets208and the rear lug308. With the takedown pin412in this position, the distal end420of the screw408may contact the adjustment surface528. In some cases where the adjustment surface528is contoured, for example sloped, the screw408may also horizontally align the upper receiver108with respect to the lower receiver104. In such a case, when the distal end420contacts the sloped adjustment surface528the screw408may re-positioned itself horizontally along that surface until the rear lug308contacts an interior surface of the lower receiver104. Once the rear lug308contacts the lower receiver104, the upper receiver108can be prevented from moving horizontally in relation to the lower receiver104.

The previous figures illustrate an example embodiment where the screw408has been previously set to a desired position to eliminate the gap120defined by the upper receiver108and lower receiver104. In some instances, however, the position of the screw408may need to be determined or adjusted to achieve the desired position of the upper receiver108. One such instance, for example, may be during initial assembly of the rifle100. As previously mentioned, rifle components can have significant tolerances that allow for ease of assembly but also create gaps between components. The amount of adjustment for reducing/eliminating the gap120may be dependent on the tolerances of the individual rifle components being assembled. Similarly, throughout the service life of the rifle100there may be other instances where the further adjustment of the upper receiver108may be desired.

The position of the upper receiver108may be adjusted by varying the distance the screw408extends into the bore310of the rear lug308. Increasing the distance that the screw408protrudes into the bore310of the rear lug308, for example, may increase the downward force applied to the upper receiver108. As a result, the upper receiver108may move further downward, reducing the gap120. Retracting the screw408from the bore of the rear lug308may increase the amount of play between the lower receiver104and the upper receiver108and thus increase the size of the gap120(if present). The position of screw408within the bore310of the rear lug308may be set at time of assembly of the rifle100or during subsequent repairs/adjustments. The screw408may be adjusted such that the takedown pin412can be removed/retracted using manual force and the gap120can be eliminated when the pin412is fully installed. Once the position of the screw408is set, the takedown pin412may be subsequently removed and re-installed any number of times without further adjustment to the position of the screw408.

FIG. 8is a cross-sectional view of the automatic rifle100illustrating another example embodiment of the present disclosure, including a takedown pin positioning mechanism700. As previously described in relation toFIG. 5, the takedown pin positioning mechanism700may include a threaded insert404and screw408installed into the rear lug308. Unlike the example embodiment shown inFIG. 5, in this case, the illustrated embodiment also includes a detent plunger708. The detent plunger708prevents the takedown pin704from being inadvertently removed from the rifle100during firing or while performing maintenance. As depicted here, the screw408and detent plunger708may be in axes parallel to one another. As a result, both the screw408and detent plunger708engage the same surface of the takedown pin704.

FIGS. 9A and 9Billustrate the takedown pin704including a cam surface824positioned along the bottom or floor of the groove812, in accordance with the present disclosure. The takedown pin704may include a head804, a shank808, a groove812and one or more surfaces to interface with the exposed end of the screw408(e.g., an installation surface820, a cam surface824, and an adjustment surface828). The head804and shank808have been previously described in relation toFIGS. 6A and 6B. As can be seen, the takedown pin704includes a groove812. The groove812may interface with the detent plunger708along the length of the takedown pin704during removal or installation of pin704. As a result, the detent plunger708maintains contact with the takedown pin704while the pin704is re-positioned. In this example case, however, the groove812may also receive the screw408. The groove812can be any size and/or shape to receive components of the detent plunger708and screw408. The screw408may contact the groove812along the installation surface820, cam surface824, and adjustment surface828. The installation surface820, in this example case, is sloped, but in other embodiments, the surface may be flat or otherwise contoured depending on the application. The configurations and operation of the surfaces820,824, and828are similar to installation surface520, cam surface524, and adjustment surface528previously described herein in relation toFIGS. 6A-6D and 7A-D.

Pivot Pin Positioning Mechanism Structure and Operation

As previously described, the upper receiver108may also move in relation to the lower receiver104about the pivot pin112. This movement about the pivot pin112may be caused by tolerances of rifle components or wear of individual components overtime. To reduce or eliminate the movement of the upper receiver108about the pivot pin112, the present disclosure discloses a pivot pin positioning mechanism. This mechanism, in operation, pivotally attaches the upper receiver108to the lower receiver104and reduces or eliminates horizontal movement between the receivers.

FIG. 10is a cross-sectional view of the automatic rifle100illustrating a pivot pin positioning mechanism900, in accordance with an example embodiment. As can be seen, the pivot pin112can be installed into the forward mounting brackets204of the lower receiver104and the forward lug304of the upper receiver108. The positioning mechanism900may include an adjustable bushing904(hereinafter referred to as bushing904). The forward lug304may include a threaded bore306for receiving bushing904, as previously described. Without installing bushing904, a gap may exist between the forward lug304and lower receiver104. The gap may allow the upper receiver108to move horizontally in relation to the lower receiver104during rifle firing. As a result of this movement, the accuracy of the rifle100may be diminished. To reduce or eliminate the horizontal movement of the upper receiver108, the bushing904may be installed.

The forward lug304of the upper receiver108may include a bushing904. The bushing904may eliminate or bridge the gap by establishing contact with the lower receiver104. The bushing904may be initially installed into the forward lug304and then its position can be adjusted to eliminate the gap. As previously described, there are many factors that contribute to creating the gap. To compensate for a range of potential sizes of the gap, the position of the bushing904within the forward lug304can be varied. The position of the bushing904can be adjusted by threading the bushing904into or out of the forward lug304. The bushing position may be adjusted until the bushing904contacts the surface of the lower receiver104and thus eliminates the gap, as shown.

FIG. 11is a perspective view of the bushing904, in accordance with the present disclosure. As previously described, the bushing904may be installed into the forward lug304of the upper receiver108to reduce/eliminate horizontal movement of the upper receiver108in relation to the lower receiver104. The bushing904may be manufactured from any suitable material that is capable of withstanding the forces generated during rifle firing, for example, stainless steel. The length of the bushing904may vary depending on the application and dimensions of any interfacing components (e.g., upper receiver108, lower receiver104, or forward lug304). As can be seen inFIG. 10, the bushing904may be of sufficient length to fill the gap while having several threads of engagement with the bore306of the forward lug304. In a more general sense, however, bushing904may be installed into the bore306, such that, the number of threads engaged is sufficient to withstand the applied loading. In this case, the length of bushing904can be approximately 0.740 inches. To ensure the thread engagement is maintained between the bushing904and forward lug304, a locking device may be installed. The locking device can be any material or device that can prevent inadvertent movement of the bushing904(i.e., unthreading or backing out), for example, a nylon pellet or a locking compound. In this example case, the bushing904may be installed using a locking compound, such as, LOCTITE® threadlocker. The bushing904may also include a bore1004. The bore1004can be of any size or shape for receiving the pivot pin112. In this case, the bore1004may have a diameter of approximately 0.276 inches. The bushing904may further include a head1008and a body or shank1016.

The bushing904may include a head1008for maintaining contact with a surface of the lower receiver104to transfer the applied forces from the upper receiver108. The head1008can be any size and shape to install the bushing904and withstand the applied forces to maintain the upper receiver108in contact with lower receiver104. In this case, the head1008may be round having approximately 0.500 inch diameter. The head1008may also include machined cut outs1012for receiving a tool. In other cases, the head1008may be in the shape of a hexagon or a square.

Attached to the head1008may be a shank1016. The shank1016may transfer the applied forces from the forward lug304of the upper receiver to the head1008. In this example case, the shank1016can be externally threaded, such that, the bushing904can be installed into the forward lug304. The external threads can be any thread size or type suitable for the applied loading. In this case, the threads may be ⅜-24UNF-2A, matching the internal threads in the bore306of the forward lug304. In other embodiments, however, portions of the shank1016may be a smooth cylindrical shape or otherwise contoured for installation of the bushing904.