CA2280553C - Conversion of firearms to fire reduced-energy ammunition - Google Patents

Abstract

A training kit is designed for use with a firearm normally having a standard bolt that is provided at the forward end with a bolt recess for receiving and embracing the head end of a standard cartridge. The training kit is provided with a training bolt having a recess that will not receive and embrace the head end of the standard cartridge by limiting placement of said standard cartridge beyond the reach of the firing pin. Rounds of reduced-energy training ammunition are provided with a head end of complementary shape that permits said head end to be seated within the recess of a conversion bolt, and therefore fired.

Description

TITLE: CONVERSION OF FIREARMS TO FIRE REDUCED-ENERGY
AMMUNITION

FIELD OF THE INVENTION
This invention relates to the fields of firearms and ammunition and provisions for modifying automatic firearms for training purposes. In particular, it relates to automatic gas-operated weapons adapted to fire reduced-energy training ammunition in a blow-back mode and to said training ammunition.

BACKGROUND TO THE INVENTION

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 adequate. An alternative type of known training ammunition, represented by United States Patent No. 5,359,937, fires a low-mass projectile relying on a special, reduced-energy cartridge designed to provide cycling of suitably-modified, recoil-operated or gas-operated automatic and semi-automatic weapons.
An advantage of the low-energy training ammunition is that it has a shorter range and lower penetration capacity than standard ammunition. This permits use of smaller, less-secure 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.

Said training ammunition, in combination with certain modifications to the weapon, 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. These modifications also serve to increase safety because the caliber of the substitute training barrel may be smaller than the diameter of the projectiles in standard 9 mm ammunition.
If an attempt is made to chamber a standard cartridge in such a training-adapted or converted firearm, the barrel will not normally admit entry of the standard projectile. This ensures

2 that such converted weapons cannot fire standard, live ammunition.

Firearms of other calibers, such as caliber .45 for pistols and 5.56 mm for automatic rifles, may also be converted to fire the same reduced-energy training ammunition using similar training barrels as described above for converted 9 mm pistols.

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 carrier assembly (for gas-operated rifles) during the beginning of their rearward motion for a period 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.
A locking mechanism couples the barrel to the slide or bolt carrier assembly for the first portion of the recoil, and then releases said slide or bolt carrier assembly, usually with the aid of a cam. Upon unlocking, the slide or bolt carrier assembly continues its rearward travel until, after the spent cartridge case has been ejected, it returns under the influence of the recoil spring to receive and chamber the next round from the magazine en route to its in-battery position.

In a training system it is necessary to omit this barrel locking mechanism and, by so doing, the recoil action becomes

3 pure blow-back of the slide or bolt carrier assembly only.
This must be done because there is not enough energy in low-energy training cartridges to precipitate sufficient recoil to unlock the barrel from the slide or bolt carrier assembly in their standard configurations.

As implied above, 5.56 mm automatic weapons, as typified by the family of gas-operated M16A2 rifles and carbines made by the 1991 Colt's Manufacturing Company Inc., can be modified to fire 9 mm reduced-energy training ammunition as represented by United States Patent No. 5,359,937. This may be done by changing the barrel in the upper receiver barrel assembly as well as altering the bolt in the bolt carrier assembly to remove the locking mechanism. While such a design ensures the exclusion of live service ammunition from being fired from a converted weapon, it is costly to implement and awkward for the user due to the excessive number of weapon components involved.

An alternative approach is to modify only the bolt carrier assembly, leaving untouched the upper receiver barrel assembly and the lower receiver buttstock assembly. In this way, the weapon can be rapidly converted to fire said reduced-energy training ammunition, by simply exchanging the service bolt carrier assembly for a training bolt carrier assembly. It is, therefore, an objective of this invention to provide a quick and easy conversion of this class of weapons

4 from its service operating configuration to a training operating configuration without modification to either said upper receiver barrel assembly or said lower receiver buttstock assembly.

This means, however, that live service ammunition would not be excluded from chambering in the standard 5.56 mm barrel, which is connected to the upper barrel receiver assembly. Thus, for this approach to be acceptable from a safety point of view, it is essential that a mechanism be included in the design of the training bolt carrier assembly, in combination with the said reduced-energy cartridge, that will positively prevent the firing of live service ammunition from a 5.56 mm weapon converted to fire said training cartridges.

It is, therefore, another objective of this invention to provide a conversion system for the class of gas-operated weapons typified by the family of M16A2 rifles and carbines that will permit the safe firing of training ammunition while positively excluding the firing of a live round of service ammunition should one be inadvertently chambered during training exercises or practice scenarios.

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 principal of the invention and the manner of

5 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.
SUMMARY OF THE INVENTION

This invention is preferably directed to gas-operated automatic weapons, as typified by the Colt M16A2 family of rifles and carbines, converted to fire reduced-energy training ammunition as represented by United States Patent No.
5,359,937. The invention is also applicable to all cases where a training bolt carrier assembly is substituted in place of a standard service bolt carrier assembly without further modification to the weapon. It is a feature of the invention that the training bolt carrier assembly is free to recoil as part of a blow-back cycling operation for reloading the weapon.

While retaining the standard pin, extractor and ejection pin, such a training bolt carrier assembly may omit the barrel locking feature present in the standard weapons by: (1) replacing the cam groove in the bolt carrier by a simple cylindrical hole through which a standard cam pin rigidly attaches the training bolt to the training bolt carrier; and (2) eliminating the gas port. Since the bolt locking lugs are, therefore, unable to rotate and engage the barrel extension in the in-battery or closed position, the converted

6 weapon operates in a pure blow-back mode when firing said reduced-energy training ammunition.

In order to exclude the possibility of firing inadvertently-chambered, live 5.56 mm standard ammunition, according to one feature of the invention the diameter of the annular recess of the front or breech end of the bolt, which houses the extractor, the ejector and the striking end of the firing pin, is reduced slightly in relation to what is required to accept standard 5.56 service ammunition.

Normally, the rim at the head end of a standard round of service ammunition fits snugly into this recess and is gripped there by the extractor, which fits over said rim and settles into the extraction groove. In this position, the primer face at the head end of the cartridge is flush against the flat bottom of the bolt recess, adjacent the tip of the retracted firing pin located therein. When the trigger is pulled, the firing pin thrusts forward and strikes the primer, thereby firing the weapon.

With a reduced diameter, however, the recess in the front end of the training bolt is not large enough to accept a standard round of 5.56 mm service ammunition. Therefore, since the depth of the recess is considerably greater than the stroke of the firing pin, there is no contact between the tip of the firing pin and the primer after the firing pin has been activated and thrust into the recess. As a result, the round

7 does not fire and the modified weapon will jam when a standard round is chambered.

The external form of the 5.56 mm invention version of the reduced-energy training ammunition as represented by United States Patent No. 5,359,937, is identical to that of the standard 5.56 mm cartridge case except for the diameter of the rim at the head of the case. This diameter is reduced so that it will fit snugly into the reduced diameter of the training bolt. Thus, said training ammunition will seat properly in said training bolt, with its head end flush against the bottom of the recess and the retracted tip of the firing pin. In this configuration, the firing pin will strike the primer and fire the weapon in the normal way when said firing pin is activated.

The foregoing summarizes the principal features of the invention and some of its optional aspects. The invention may be further understood by the description of the preferred embodiments, in conjunction with the drawings, which now follow.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the major components of a typical prior art rifle in the class of M16A2 gas operated rifles and carbines.

8 Figures 2A and 2B are respectively side and end views of a prior art bolt from the bolt assembly carrier of Figure 1.
Figures 3A and 3B are the same views as in Figures 2A and 2B of a training bolt according to the invention.

Figure 4A is a top view of a prior art bolt carrier from the bolt carrier assembly of Figure 1.

Figure 4B is a side view of a prior art cam pin from the bolt carrier assembly of Figure 1.

Figure 5 is the same top view as in Figure 4A of a training bolt carrier according to the invention.

Figure 6 is a side cross-section of a training bolt carrier assembly of Figure 5 according to the invention.
Figures 7A and 7B show side and end views of a prior art standard 5.56 mm service cartridge.

Figures 8A and 8B show side and end views of a 5.56 mm reduced-energy training cartridge as represented by United States Patent No. 5,359,937.

Figure 9 depicts a reduced-energy training cartridge fitted into the recessed end of a training bolt according to the invention at the moment that the firing pin has just been activated and struck the primer.

Figure 10 depicts a live 5.56 mm standard service round unable to enter the front-end bolt recess of a training bolt according to the invention and, therefore, not coming into

9 contact with the firing pin at the moment when said firing pin is activated.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In Figure 1 the four major groups of a typical prior art rifle in the class of 5.56 mm M16A2 gas operated rifles and carbines are shown: upper receiver barrel assembly 1, bolt carrier assembly 2, lower receiver buttstock assembly 3, and magazine 4. According to the invention, only bolt carrier 2 will be altered to convert the prior art weapon to a training configuration that will fire a recoil activating round, such as a reduced-energy training ammunition as represented by United States Patent No. 5,359,937 in a 5.56 mm version (training cartridge 21 in Figure 8A).

Figures 2A and 2B show a prior art bolt 5, which is part of prior art bolt carrier assembly 2. Bolt 5 contains locking hole 6, gas seal 7, bolt locking lugs 8, front end recess 9, ejector 10, firing pin 20 and extractor 12. The diameter of front end recess 9 is denoted by the letter A.
Figures 3A and 38 depict training bolt 13 of the invention as modified with respect to prior art bolt 5. Since the training configuration is not gas operated, the gas seal 7 has been eliminated to reduce the cost of fabrication. Locking hole 6, bolt locking lugs 8, ejector 10, firing pin 20 and extractor 12 are all identical to the prior art. Training recess 14, however, differs from prior art recess 9 in that its diameter, denoted by the letter B, is smaller than prior art diameter A (i.e., B < A) by approximately 0.020 inch, although this may vary depending on the design of the training cartridge 21 (Figure 8A).

Figure 4A shows a prior art bolt carrier 15, which is another part of prior art bolt carrier assembly 2, containing cam groove 16 and gas port 16A. Figure 4B shows prior art cam pin 17, which goes through both cam groove 16 of prior art bolt carrier 15 and locking hole 6 of prior art bolt 5 after bolt 5 is inserted into bolt carrier 15 to form prior art bolt carrier assembly 2.

Figure 5 depicts training bolt carrier 18 of the invention as modified from prior art bolt carrier 15. Since the training configuration is not gas operated, the gas port 16A has been eliminated to reduce the cost of fabrication. In addition, prior art cam groove 16 has been replaced by locking hole 19. After training bolt 13 is inserted into training bolt carrier 18 to form training bolt carrier assembly 18A, as illustrated in Figure 6, locking hole 6 of training bolt 13 is aligned with locking hole 19 of training bolt carrier 18 so that cam pin 17 can be inserted through said locking holes 19 and 6 to rigidly attach said training bolt 13 to said training bolt carrier 18.

Figures 7A and 7B depict a standard 5.56 mm service cartridge 23 containing standard primer 24, head end rim 25 and extraction groove 26. The diameter of rim 25 is denoted by the letter C.

Figures 8A and 8B depict reduced-energy training cartridge 21, as represented by United States Patent No.
5,359,937, in contrast to prior art cartridge 23. Prior art primer 24 may or may not differ from training primer 22, while extraction groove 26 is identical for both cartridges. Both rounds 21,23 have case dimensions that allow them to be chambered, and fully seated in the chamber portion of the barrel of the firearm. The diameter D of training rim 27, however, is slightly smaller than the diameter of prior art rim 25 (i.e., D< C), this difference being approximately 0.020 inch, depending on the diameter B of recess 14 of training bolt 13 (Figure 3B). This difference in diameter is intended to ensure that the recess 14 of training bolt 13 will not receive a standard, prior art cartridge containing prior art rim 25.
Since only the training bolt carrier assembly 18A is different after a prior art M16A2-type weapon has been converted to fire said reduced-training ammunition 21, it is possible that a live round of 5.56 mm service ammunition 23 may be inadvertently chambered in the training weapon during a training session. An object of the invention is to ensure that a standard round will not be fired by a modified weapon.
The manner in which the possible firing of such a live round of service ammunition is excluded by the invention is illustrated in Figures 9 and 10.
As already described, the diameter of recess 14 of training bolt 13 (diameter B in Figure 3B) and the rim diameter 27 of training round 21 (diameter D in Figure 8B) are both slightly smaller than the corresponding dimensions for prior art bolt 5 (diameter A in Figure 2B) and a standard service round of 5.56 service ammunition 23 (diameter C in Figure 7B). Further, diameter D of rim 27 of reduced-energy training cartridge 21 is such that the head end 28 of reduced-energy training cartridge 21 will fit snugly into diameter B
of recess 14 of training bolt 13 and be gripped there by the extractor 12, which fits over said rim 27 and settles into extraction groove 26. In this position, face 28 of primer 22 is flush against both the flat bottom of said recess 14 and striker tip 11 of retracted firing pin 20 located therein.
When the weapon is activated, firing pin 20 thrusts forward and its striker tip 11 strikes primer 22, as shown in Figure 9, thereby igniting primer 22 and firing reduced-energy training round 21.

Again as previously described, the diameter of rim 25 of a standard round of 5.56 mm service ammunition 23 (diameter C
in Figure 7B) is larger than the diameter of recess 14 of training bolt 13 (diameter B of Figure 3B), having been designed to fit into diameter A of recess 9 of prior art bolt 5. Thus, should a round of live service ammunition 23 be chambered in the upper receiver barrel assembly 1 of a M16A2 weapon converted to fire reduced-energy training ammunition 21, the diameter C of rim 25 of said standard cartridge 23 will not fit into diameter B of recess 14 of training bolt 13, as shown in Figure 10. Since the depth of recess 14 is approximately 0.125 inch and the maximum stroke of firing pin 20 is only about 0.025 inch, striker tip 11 of firing pin 20 does not nearly reach primer 24, hence said live service round is not fired and the weapon will jam to signal that there is a problem.

Many rounds of various types of standard 5.56 mm service ammunition have been tested in M16A2 rifles converted to fire reduced-energy training ammunition to demonstrate the live-fire exclusion feature of the invention with complete success. Similarly, large numbers of 5.56 mm reduced-energy training ammunition with reduced rim diameters, as represented by a 5.56 mm version of united states Patent No.

5,359,937, have been fired from the same converted rifles to demonstrate conclusively that only the bolt carrier assembly need be changed to yield, in conjunction with the live-fire exclusion feature, a reliable and safe training weapon system.

The invention, while demonstrated by the M16A2 rifle is applicable to all firearms wherein a conversion to fire low-energy ammunition is combined by the safety features of live-fire exclusion.

CONCLUSION
The foregoing constitutes a description of specific embodiments showing how the invention may be applied and put into use. These embodiments are only exemplary. The invention in its broadest and more specific aspects is further described and defined in the claims which follow. These claims, and the language used therein, are to be understood in terms of the variants of the invention which has been described. They are not to be restricted to such variants, but are to be read as covering the full scope of the invention as is implicit within the invention and the disclosure that has been provided herein.

Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A firearm having:
a) a standard barrel and standard chamber of respective given diameter that are dimensioned to fire standard ammunition, the standard ammunition having a cartridge with a head end and a case that are of a diameter that is substantially equal to the diameter of said chamber;
b) a standard upper receiver assembly for connection to said standard barrel;
c) a standard lower receiver buttstock assembly;
d) a magazine; and e) a training bolt carrier assembly comprising a training bolt carrier and a training bolt with a firing pin and training bolt recess with a base through which the firing pin will operate by advancement into said recess upon firing, said training bolt recess being dimensioned or shaped to exclude the seating of the head end of said standard ammunition in said bolt recess whereby the firing of standard ammunition is precluded, said training bolt carrier assembly being dimensioned for mounting in the firearm with said training bolt and training bolt carrier being free to recoil upon firing so as to effect cycling of the firearm through a blow-back operation, said firearm being in combination with a reduced-energy cartridge having:

f) a case dimensioned to allow said reduced-energy cartridge to seat fully in the standard barrel chamber of said firearm, g) a head end which is dimensioned or shaped to seat fully in the training bolt recess, within reach of said firing pin upon firing, and h) a case that is divided into two portions that expand longitudinally upon firing to effect cycling of the weapon through blow-back operation.

2. A firearm as in claim 1 wherein the training bolt recess is circular and is of a reduced diameter that will exclude the reception and seating of the head end of a standard cartridge, and the head end of the reduced-energy cartridge is circular and of a diameter that will allow said reduced energy cartridge head end to seat in said training bolt recess.

3. A firearm as in claim 2 wherein the training bolt is fixed to the training bolt carrier for recoil of said training bolt and training bolt carrier as a unit upon firing as part of said blow-back operation.

4. A firearm as in claim 1 wherein the base of the training bolt recess comprises a protrusion which will preclude the seating of a standard cartridge the training bolt recess, and the reduced-energy cartridge is provided at its head end with a recess that is of complementary shape to said protrusion to permit the head end of the reduced-energy cartridge to seat in said training bolt recess.

5. A firearm as in claim 4 by wherein the training bolt is fixed to the training bolt carrier for recoil of said training bolt and training bolt carrier as a unit upon firing as part of said blow-back operation.

6. A firearm as in claim 1 wherein the training bolt is fixed to the training bolt carrier for recoil of said training bolt and training bolt carrier as a unit upon firing as part of said blow-back operation.

7. A standard firearm in combination with a training kit for use in converting the standard firearm into a training configuration for firing reduced energy ammunition, the standard firearm having:

a) a standard chamber of a given diameter fitted within a standard barrel and b) a standard bolt provided at its forward end with a standard bolt recess for receiving and embracing the head end of a standard cartridge having a casing and head end both of a diameter that is substantially the same as the chamber diameter, c) a standard receiver with a bolt carrier assembly that receives said standard bolt, and standard bolt carrier, wherein said training kit comprises:

d) a training bolt with a training bolt firing pin and a training bolt recess fitted within a training bolt carrier wherein the training bolt firing pin and training bolt recess are dimensioned or shared to exclude the reception and seating of the head end of said standard cartridge, whereby, with the standard cartridge loaded in said chamber and the training bolt installed in the firearm, the training bolt recess will not embrace the head end of the standard cartridge so that when said firing pin is released to advance into the training bolt recess, the head end of the standard cartridge is beyond the reach of the training bolt firing pin, said training bolt and training bolt carrier being dimensioned for mounting in the standard receiver of the firearm in a position to serve in place of the standard bolt and standard bolt carrier, but with said training bolt being free to recoil upon firing so as to effect cycling through a blow-back operation, and e) a reduced-energy cartridge having a casing that is dimensioned to be chambered in said standard chamber and having a head end that is dimensioned or shaped to be received and embraced by the training bolt recess to permit firing of said reduced-energy cartridge by said firing pin, said reduced-energy cartridge being provided with a case that is divided into two portions that expand longitudinally upon firing to effect cycling of the weapon through blow-back operation whereby the standard firearm is convertible to fire said reduced energy cartridge, excluding the chambering of a standard cartridge.

8. A standard firearm in combination with a training kit as in claim 7 wherein the training bolt recess is circular, having a reduced diameter that will exclude the reception and seating of the head end of a standard cartridge, and the head end of the reduced-energy cartridge is of a circular diameter that will allow said reduced-energy cartridge head end to seat in the training bolt recess.

9. A standard firearm in combination with a training kit as in claim 8 wherein the training bolt is fixed to the training bolt carrier for recoil of said training bolt and training bolt carrier as a unit upon firing as part of said blow-back operation.

10. A standard firearm in combination with a training kit as in claim 7 wherein a base of the training bolt recess comprises a protrusion which will preclude the seating of a standard cartridge in the training bolt recess, and the reduced-energy cartridge is provided at its head end with a recess that is of complementary shape to said protrusion to permit the head end of the reduced-energy cartridge to seat in the training bolt recess.

11. A standard firearm in combination with a training kit as in claim 10 wherein the training bolt is fixed to the training bolt carrier for recoil of said training bolt and training bolt carrier as a unit upon firing as part of said blow-back operation.

12. A standard firearm in combination with a training kit as in claim 7 wherein the training bolt is fixed to the training bolt carrier for recoil of said training bolt and training bolt carrier as a unit upon firing as part of said blow-back operation.