Patent Application
20180080732
The present invention relates to fully automatic or select-fire firearms. More particularly, it provides a device for actuating the auto sear in an AR-platform firearm having a shortened bolt carrier.
An AR-pattern firearm (which includes, but is not limited to, the AR15, AR10, M16, M4, and clones of these) has separable upper and lower receivers. The lower receiver houses the fire control group of parts, including the hammer, trigger, disconnector, and, when capable of fully automatic fire (i.e., a machine gun), an auto sear. The upper receiver houses a longitudinally reciprocating bolt and bolt carrier. In a typical configuration, the bolt carrier extends substantially the entire length of the upper receiver and moves rearwardly beyond the confines of the upper receiver when the action cycles. In this typical configuration, a recoil spring and buffer are housed in an extension positioned reward of the upper receiver.
In compact versions, in which the recoil spring is housed within the upper receiver, usually actuated by a gas piston system, or having a simple blowback bolt, such in a pistol caliber carbine, there is no need for the bolt carrier to extend the full length of the upper receiver or to reciprocate beyond the confines of the upper receiver. Operating systems of this type allow for the use of a folding stock and/or eliminate the need for an extension to house the recoil spring and buffer in a pistol configuration. However, these compact bolt carriers are unable to trip the auto sear, which has to be tripped just prior to the bolt carrier and bolt returning to its full in-battery position, where it is situated in a standard lower receiver without significant modification to the shortened bolt carrier.
Others have proposed solutions to this challenge with “lost motion” or “slip” linkage devices that attach to and require modification of the upper receiver. For example, U.S. Pat. No. 8,667,882, issued Mar. 11, 2014, shows one such device which attaches to the upper receiver and reciprocates on elongated grooves or channels machined on the interior of the upper receiver. Another example is shown by U.S. Pat. No. 9,151,558, issued Oct. 6, 2015, which uses a sear trip bar that is held slidably captive in a groove machined on one side of the interior of the upper receiver. In rim-fire conversion devices for AR-platform firearms, auto sear trip bars have been integrated into or attached to an elongated structure that replaces the standard bolt carrier, or that are carried within the upper receiver. One example is shown in U.S. Pat. No. 3,776,095, issued Dec. 4, 1973.
One example embodiment provides an auto sear trip link for use in a firearm having separable upper and lower receivers, an auto sear, and a bolt carrier that longitudinally reciprocates substantially completely within the upper receiver without extending rearward beyond a rear end of the receivers. The link includes a pair of laterally spaced apart longitudinally extending members unconnected to the upper receiver and configured to fit at least partially between lateral sidewalls of the lower receiver and edges of a bottom opening in the upper receiver. The link has a forward portion configured to rest on an upper surface of the lower receiver and a rearward portion configured to be supported by an auto sear installed in the lower receiver. At least one engagement horn extends upwardly from the forward portion of the member. A first rear crossmember interconnects a rearward portion of the longitudinally extending members and is configured to operatively engage the auto sear. A reciprocating bolt carrier slides within the upper receiver between a forward, in-battery position and a rearward, recoil position. The carrier has at least one boss at a rear end thereof configured to engage the horn as the bolt carrier reaches an in-battery position, thereby moving the trip link and tripping the auto sear to initiate a firing cycle.
Another example embodiment provides a firearm auto sear trip linkage, including a longitudinally extending link member having a pair of laterally spaced apart elongated beams, a forward end and a rearward end. The link member is unconnected to a firearm upper receiver when installed and is configured to fit at least partially between lateral sidewalls of a firearm lower receiver and edges of a bottom opening in the upper receiver. The link member has a forward end portion configured to rest on an upper surface of the lower receiver and a rearward end portion configured to be supported by an auto sear in the lower receiver. At least one engagement horn extends upwardly from a forward end portion of the link member and is configured to be operatively interfaced with a bolt carrier of the firearm. A rear cross-member connects the beams at the rearward end and is configured to operatively interface with the auto sear.
Another example embodiment provides a firearm including an upper receiver, a lower receiver, a bolt carrier that longitudinally reciprocates substantially completely within the upper receiver without extending rearward beyond a rear end of the receivers, and an auto sear in the lower receiver. The bolt carrier has at least one longitudinal bottom groove and at least one boss having a portion longitudinally aligned with a rear end of the bottom groove. A longitudinally extending link member with forward and rearward ends includes a pair of laterally spaced apart and longitudinally extending beams, a horn at the forward end configured to pass through the bottom groove and to operatively interface with the boss, and a rear crossmember interconnecting a rearward portion of the beams configured to operatively interface with the auto sear. The link member is unconnected to the upper and lower receivers, and is supported at the rearward end by the auto sear and at the forward end by resting on an upper surface of the lower receiver such that, upon sufficient forward displacement of the bolt carrier within the firearm, the link member trips the auto sear to initiate a firing cycle.
Other aspects, features, benefits, and advantages of the present invention will become apparent to a person of skill in the art from the detailed description of various embodiments with reference to the accompanying drawing figures, all of which comprise part of the disclosure.
Like reference numerals are used to indicate like parts throughout the various figures of the drawings, wherein:
With reference to the drawing figures, this section describes particular embodiments and their detailed construction and operation. Throughout the specification, reference to “one embodiment,” “an embodiment,” or “some embodiments” means that a particular described feature, structure, or characteristic may be included in at least one embodiment. Thus appearances of the phrases “in one embodiment,” “in an embodiment,” or “in some embodiments” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the described features, structures, and characteristics may be combined in any suitable manner in one or more embodiments. In view of the disclosure herein, those skilled in the art will recognize that the various embodiments can be practiced without one or more of the specific details or with other methods, components, materials, or the like. In some instances, well-known structures, materials, or operations are not shown or not described in detail to avoid obscuring aspects of the embodiments.
The structure and operation of AR-pattern firearms in both semi-automatic and fully automatic modes are generally well known. As previously described, the bolt carrier in a typical configuration includes a reward extension capable of tripping the auto sear as the bolt goes into battery when the selector is positioned to “auto.” An example is shown and described in U.S. Pat. No. 3,045,555 issued Jul. 24, 1962. This rearward extension of the bolt carrier is unnecessary and not usually found in configurations where the recoil spring is housed within the upper receiver, rather than in a rear housing extension.
The present invention provides a mechanism for using such compact bolt carrier designs without modification of or connection to either the upper or lower receiver. It provides an auto sear trip linkage that is independent of both the upper and lower receivers and which may be used as a “drop in” unit to allow an upper receiver assembly otherwise configured for semi-automatic fire to be used in full-auto mode with a standard, full-auto capable AR-pattern lower receiver.
Referring first to
Referring also to
Orientation of the longitudinal beams 30 and flanges 28 provides structural rigidity for the linkage member 10, which is supported only at its ends 12, 16. The vertical orientation provides a web resistant to vertical forces. The horizontal orientation of the flange 28 strengthens the web against lateral forces. This allows the linkage member 10 to be very lightweight and use minimal material, while being resistant to deformation. Operational forces on the linkage member will be primarily longitudinal tension as engagement of the bosses 24 against the horns 22 at the forward end 16 pulls it forward as the bolt carrier 26 approaches the in-battery position and engagement with the auto sear 14, biased by the spring 44, at its rearward end 12 pulls it rearward when the bosses 24 disengage from the horns 22 when the bolt carrier 26 travels rearward or is locked back.
Referring now to
Referring to
As is well known with respect to gas-operated auto-cycling firearms, when a cartridge (not shown) is discharged, propellant is ignited creating gas pressure and pushing the projectile through the bore of the barrel. Some of the gas pressure from the burning propellant is diverted through a port in the barrel and provides energy to cycle the action. As shown in
If ammunition remains, the recoil spring 52 then returns the bolt carrier 26 assembly forward, as shown in
While one embodiment of the present invention has been described in detail, it should be apparent that modifications and variations thereto are possible, all of which fall within the true spirit and scope of the invention. Therefore, the foregoing is intended only to be illustrative of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not intended to limit the invention to the exact construction and operation shown and described. Accordingly, all suitable modifications and equivalents may be included and considered to fall within the scope of the invention, defined by the following claim or claims.
