In military and police firearms applications almost all of the ammunition consumed is used in training. For some training purposes, however, normal ammunition is not appropriate. An alternative type of ammunition, which has much lower energy and is represented by U.S. Pat. No. 5,359,937 (adopted herein by reference), fires a low-mass projectile relying on a special, low-energy cartridge designed to provide cycling of suitably modified, recoil-operated automatic and semi-automatic weapons. The cartridge case portion of this low-energy training ammunition expands telescopically on firing to provide force to cycle the firearm. An advantage of low-energy training ammunition is that it has a shorter range and lower penetration capacity than standard ammunition. This permits use of smaller firing ranges as training facilities. If standard ammunition were accidentally employed in these facilities, unexpected dangers would arise from the increased striking power and range of standard ammunition.
Low-energy training ammunition, in combination with certain modifications to the weapon being used, allows normal recoil and cartridge case ejection through a pure blow-back action. Such a system, when firing appropriate marking cartridges, makes for effective close-range, force-on-force training. This system enhances the realism and training value of interactive scenario tactical training because it allows trainees to use their service weapons in a representative manner in exercises simulating, for example, counter-terrorism, close quarters combat, trench clearing, fighting in wooded areas, urban fighting, and protection of dignitaries.
Modifications required to permit cycling of 9 mm automatic or semi-automatic weapons while firing low-energy ammunition, for example, generally include replacing or modifying the barrel and sometimes replacing or adding one or two other components, depending on the weapon involved. Such modifications are exemplified by U.S. Pat. Nos. 5,983,773; 6,276,252 and 6,442,882. These modifications may also serve to increase safety because the calibre of the substitute training barrel may be smaller than the diameter of the projectile in standard 9 mm ammunition. If an attempt is made to chamber a standard cartridge in such a training-adapted firearm, the barrel will not normally admit entry of the standard projectile. This ensures that such converted weapons cannot fire standard, live ammunition.
The same approach can be adopted for converting automatic 5.56 mm gas-operated firearms, for example, to fire low-energy training ammunition. However, using a bore diameter different than 5.56 mm to prevent the chambering of normal service ammunition involves modifications to the weapon that can become prohibitively expensive. U.S. Pat. No. 6,625,916, the contents of which are incorporated herein by reference has overcome this problem in M16A2 rifles and carbines made by the Colt's Manufacturing Company, LLC, for example, by limiting the modifications to the bolt carrier assembly. Safety is ensured by having a training bolt carrier assembly, comprising in part a training bolt having a recess on its bearing face which accommodates low-energy training cartridges while ensuring that conventional ammunition does not seat, thereby avoiding the accidental firing of live ammunition. This same live fire exclusion safety feature can also be applied to similar weapons such as, for example, the 5.56 mm FNC assault rifle made by FN Herstal S.A. of Belgium.
When firing standard ammunition, with its abundant associated energy, it is necessary in many weapons to lock the barrel to the slide (for pistols), or to the bolt assembly for gas-operated automatic rifles, during the first portion of the firing cycle. These parts must be locked together for a period of time long enough for the projectile to exit the barrel muzzle while the breech is still closed. This allows the chamber pressure to drop before the breech opens to extract and eject the spent cartridge case. In rifles and carbines, the locking mechanism that couples the barrel to the bolt assembly for this first portion of the recoil process, and then releases said bolt assembly, is activated usually with the aid of a camming interface between the bolt and the bolt carrier assembly. Upon unlocking, the bolt carrier assembly continues its rearward travel until, after the spent cartridge case has been ejected, it returns under the pressure of the recoil spring to pick-up and chamber the next cartridge from the magazine, en route to its in-battery position.
In a training system using low energy cartridges, it is necessary to omit this barrel locking mechanism and, by so doing, the recoil action becomes pure blow-back of the bolt carrier assembly. This must be done because there is not enough energy in low-energy training cartridges, as represented by U.S. Pat. No. 5,359,937 to furnish sufficient recoil to unlock the barrel from the bolt carrier assembly in their standard configurations.
In the 5.56 mm FNC assault rifle, after replacing the standard bolt carrier assembly by a training bolt carrier assembly to permit the weapon to fire low-energy training cartridges, the absence of a locking mechanism between the barrel and the bolt assembly allows the recoiling bolt assembly to bounce off the base of the cartridge case, after chambering of the low-energy training cartridge in full automatic or three-round burst modes. The resulting, unwanted rebound sometimes leads to “short cycling” of the second or subsequent rounds, wherein the weapon misfires. Such rebound disrupts the synchronization of the firing cycle, resulting in a possible misfire since, in this instance, if the hammer is activated to hit the firing pin while the bolt carrier assembly is rebounding backward, it may not reach the cartridge primer. It is, therefore, an objective of this invention to provide, for the FNC 5.56 mm assault rifle when converted to fire low energy training ammunition, a means of attenuating possible rebound of the bolt when it chambers the cartridge.
It is a further objective of this invention to extend this method of rebound attenuation to other automatic and semi-automatic weapons of the blow-back class generally, and particularly weapons converted to fire low-energy training cartridges. While the invention is preferably directed to gas-operated automatic and semi-automatic weapons, as typified by the FN Herstal's FNC assault rifle, converted to fire low-energy training ammunition as represented by U.S. Pat. No. 5,359,937, the invention is also applicable to all blow-back automatic weapons where there is a need to ensure that the bolt or equivalent will not bounce or rebound off the base of the cartridge case during the feeding cycle so as to cause a misfire.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention and the manner of its implementation. The invention in its broadest and more specific forms will be further described and defined, in each of the individual claims which conclude this specification.