Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
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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
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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
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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
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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
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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
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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.
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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
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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
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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.
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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
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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
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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-
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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.
