Note: Descriptions are shown in the official language in which they were submitted.
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ROUND OF RIFLE AMMUNITION AND
METHOD FOR MAKING SAME
RELATED APPLICATIONS
This application claims the benefit of provisional application
S.N. 60/ 174,797, filed January 6, 2000, entitled: ROUND OF
RIFLE AMMUNITION AND METHOD FOR MAKING SAME.
BACKGROUND OF INVENTION
This invention relates to rifle ammunition of 50 caliber or
less, particularly to ammunition for rifles and wherein the
projectile thereof is propelled from the rifle barrel at a subsonic
velocity, and to methods for the manufacture of rifle ammunition.
In certain shooting situations, it is desirable that the
projectile fired from a rifle travel at less than supersonic velocity.
This shooting situation commonly occurs in the course of military
and law enforcement activities, such as in sniper fire or other
activity where it is desired that the location of the shooter not be
detectable by reason of the sound associated with the firing of the
rifle and the path of travel of the projectile.
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Rifle ammunition heretofore intended to provide for subsonic
velocity of the projectile thereof upon firing of the ammunition
commonly has been manufactured by simply reducing the quantity
of gun powder loaded into the case of each round
of the ammunition. This procedure leaves a very substantial
portion of the interior volume of the case void of either powder
and/or projectile. The gun powder within the case, therefore, is
free to flow into one or the other end of the case, depending upon
whether the rifle being used is aimed upwardly from the horizontal
or downwardly from the horizontal. When the powder shifts to the
leading end of the case (adjacent the projectile and away from the
primer in the closed end of the case), the flame generated upon the
firing pin striking the primer must pass through a void space
between the primer and the powder. This situation creates at least
two undesirable factors, namely: (a) delay in ignition of the powder
and/or (b) poor exposure of the powder to the flame pattern. The
first of these factors can be so serious as to cause the shooter to
believe that he has experienced a misfire, or to cause the shooter
to pull his sight off the target. The second of these factors may
result in insufficient ignition of the powder and a burn pattern
which causes inconsistent propulsion of the projectile from the
rifle, hence inability of the shooter to hit a desired target. When the
powder shifts toward the primer-containing closed end of the case,
these factors are generally reversed, causing supersonic velocity of
the projectile and other deleterious results.
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When firing ammunition from a rifle operated in either the
automatic or semi-automatic firing mode, and wherein the bolt of
the rifle is gas-operated off the gases generated by
the burning gun powder within the case, successful consistent
operation of the bolt is dependent upon the maintenance of a
minimum gas pressure within the barrel of the rifle behind the
projectile as it moves along the barrel and past the gas port leading
from the barrel to the bolt-actuating mechanism. Failure to
develop and maintain this minimum gas pressure results in failure
of the bolt to operate. Known prior art rifle ammunition which is
represented to be capable of firing a projectile at a subsonic
velocity is known for its inability to consistently develop the
required minimum gas pressure for operation of the bolt, hence is
normally not suitable for use in rifles having gas-operated bolts.
It is therefore an object of the present invention to provide a
round of rifle ammunition which consistently (from round to
round) propels its projectile from the rifle at less
than supersonic velocity.
It is another object to provide a "subsonic" round of rifle
ammunition which, when fired in a rifle having a gas-operated bolt,
consistently (from round to round) successfully operates the bolt of
the rifle.
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It is another object to provide a round of ammunition
suitable for firing from a rifle having a gas-operated bolt wherein
the projectile for the round is propelled from the
rifle at a subsonic velocity and wherein the gas pressure developed
within the rifle barrel and the bolt-actuating mechanism
consistently performs the bolt actuation from round to round of
the ammunition.
It is another object to provide a method for the manufacture
of a round of rifle ammunition suitable for use in a rifle having a
gas-operated bolt and wherein the rifle is operated in an automatic
or semi-automatic mode and the projectile of the round exits the
rifle barrel at a subsonic velocity.
Other objects and advantages of the present invention will be
recognized from the present specification, including the claims and
the drawings appended hereto.
BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1 is a representation, part in section, of a round of
rifle ammunition embodying various of the features of the present
invention;
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Figure 2 is a representation, part in section, of another
embodiment of the round of rifle ammunition depicted in Figure
1;
Figure 3 is an exploded view of various of the components
of a round of ammunition in accordance with one aspect of the
present invention;
Figure 4 is a representation of a portion of the trailing end of
a further embodiment of a projectile having an alternative
structure for positionally stabilizing the gun powder within the
case of a round of ammunition.
Figure 5 is a representation of a still further
embodiment of a projectile having an alternative structure for
positionally stabilizing the gun powder within the case of a
round of ammunition.
Figure 6 is a side view of a cotton fiber disc which is
also depicted as a component of Figure 3; and
Figure 7 is a side view of a paper disc which is also depicted
as a component of Figure 3.
SUMMARY OF INVENTION
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In accordance with one aspect of the present invention there
is provided a round of rifle ammunition, particularly for use in
rifles having a gas-operated bolt and capable of
being fired in the automatic or semi-automatic mode. The
ammunition of the present invention is structured to propel the
projectile of a round of the ammunition from the rifle at less than
supersonic velocity, consistently from round to round of the
ammunition. Further, each round of the ammunition, when fired,
develops and sustains within the rifle, not less than that minimum
gas pressure which consistently successfully operates the bolt of
the rifle when the rifle is fired in the automatic or semi-automatic
mode.
In accordance with one feature of the present invention, gun
powder is deployed and positionally stabilized within that end of
the case of each round of ammunition adjacent the primer,
irrespective of the positional attitude of the rifle at the time of
firing. Moreover, such positionally stabilized gun powder is
substantially free of void spaces which might introduce random
excursions in the ignition, burn rate, etc. of the gun powder
sufficient to adversely affect either the velocity of the projectile fired
from the rifle or the build-up and sustainment of sufficient gas
pressure for consistent successful operation of the gas-operated
bolt of the rifle.
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Another aspect of the present invention relates to the ability
to use a tapered projectile with its enhanced flight characteristics,
hence accuracy of delivery of the projectile to a target, when fired
at a subsonic velocity. This tapered projectile further develops less
surface friction, hence less heat, as it travels through the rifle
barrel, thereby reducing the buildup of barrel heat during
sustained firing cycles.
Further, the tapered projectile has been found to produce
less wear and fouling of the internal bore of the barrel. The
ammunition of the present invention has been found to be suitable
for firing in a standard military M 16M4 rifle (5.56 mm) having a
14.5 inches long barrel of seven twist.
DETAILED DESCRIPTION OF INVENTION
In Figure 1 there is depicted one embodiment of a round of
rifle ammunition 12 in accordance with the present invention and
including a standard case 14 having a trailing end 16, an open
leading end 18, and a body 20 which includes a generally hollow
tubular portion 22 that transitions into a "necked down" tubular
portion 24. The trailing end of the case is substantially closed and
includes a primer port 26 within which there is disposed a primer
28. The primer port is accessible from exteriorly of the case and
includes a flame port 30 leading therefrom and into the interior
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volume 32 of the case. Notably, the flame port 30 comprises a
straight through bore having an inwardly terminal opening 32
whose rim 34 is defined by the junction of the straight wall of the
through bore with the inside bottom wall 36 of the case which is
oriented normally of the wall of the through bore. By this means,
the rim 34 is sharply defined so that a flame generated by the
firing of the primer exits the flame port in a substantially
collimated flame that projects itself into the adjacent powder
charge 38 to ignite the powder charge interiorly thereof and along
the axial length of the powder charge. When the powder charge is
disposed adjacent the primer and the trailing end of the case, the
powder charge thus burns uniformly substantially radially
outwardly from its axial centerline, creating a uniform and
consistently sustained burn of the powder, resulting in uniform
and consistently sustained buildup of gas pressure within the rifle
barrel sufficient to operation the gas-operated bolt fo the rifle.
As noted, the charge of gun powder 38 is disposed within the
case adjacent the trailing end of the case to a level 52 located
within the body portion of the case. In accordance with one aspect
of the present invention, this charge of gun powder occupies
materially less than the interior volume of the case, in one
embodiment only about 50% of the interior volume of the case.
This volume of slow-burning gun powder assures that there will be
sufficient gas pressure built up to propel a projectile 40, disposed
in and closing the leading end of the case, from a rifle at a
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subsonic velocity while simultaneously generating and sustaining
that minimum gas pressure within the rifle as will operate the bolt
of the rifle. The choice of the particular gun powder to be
employed in a given caliber round of ammunition, the volume of
the chosen gun powder, its burn rate, etc. have heretofore been
thought by those skilled in the art to require relative small charges
of a fast-burning powder, such as a pistol powder. To the
contrary, the present inventor employs a gun powder which is
industry rated as being a very slow burning powder. As noted,
irrespective of the gun powder type actually used, the present
invention addresses the problem of keeping the powder charge
positionally stable within the case and adjacent the trailing end of
the case, preferably with few or no void spaces within the volume
of powder. To this end, the present inventor has found that a
powder charge which does not fully fill the interior volume of the
case can be held as a coherent charge within the case and adjacent
the trailing end of the case, hence adjacent the primer, by means
of a disc 50 which is inserted through the open end of the case
proximate the level 52 of the gun powder in the case. This disc is
self supporting and of a circumference which substantially
matches the internal circumference of the case at the location of
the top surface 52 of the powder charge held in the case. The disc
50 is overlaid upon the top surface of the powder within the case
and preferably has its circumference in frictional engagement with
the inner wall of the case. Thereafter, the proximal end 56 of the
elongated projectile 40 is inserted into the case through the open
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leading end of the case. In the depicted embodiment, the proximal
end 56 of the projectile is flat and defines a flat surface 58 which is
oriented substantially normal to the length dimension of the
projectile. In a preferred embodiment, this flat proximal end of the
projectile extends to a location which is contiguous to and
preferably contacting, but not pressing against the top surface 60
of the disc or is disposed spaced apart from the top surface of the
disc by a short distance, 0.1 inch for example, but not farther away
from the disc than by a distance greater than about one-half the
diameter of the disc.
The disc 50, being of a diameter greater than the internal
diameter of the necked-down portion of the case, must be
sufficiently flexible as permits the disc to be folded to the extent
necessary for it to pass through the necked-down portion of the
case, and sufficiently resilient to substantially resume its flat disc
geometry once it is inside the body portion of the case. One
suitable disc for use in the present invention comprises a disc die-
cut from common "target stock" paper used in the manufacture of
rifle targets. "100 yard target stock" purchased from Hohen Sales
of Wright City, MO. has been found to be a suitable paper. This
paper is about 0.014 inch thick and has a basis weight less than a
postal card stock, for example. The disc may be die cut from a
sheet of the paper. Such die-cutting of the disc results is
compression of the thickness of the paper around the
circumferential margin of the cut disc, to a thickness of about
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0.010 inch, hence a stiffening of the disc within such
circumferential margin.
This stiffening has been found to be useful in the ability of
the disc to resist that deformation thereof which might lead to the
escape of powder particles from the powder charge and into that
portion of the interior volume of the case which is on the leading
end side of the disc when the disc is disposed within the case in
engagement with the top surface of the powder charge. It is
contemplated that other paper stock may be employed, as well as
other materials of construction for the disc. In any event, it is of
importance that the disc be rapidly disintegrated in the presence of
the burning of the powder charge so that no material unburned
portion of the disc will pass into the gas transfer system employed
in connection with the operation of the bolt of the rifle.
The round of ammunition depicted in Figure 1 includes a
projectile 40 preferably formed from a core 62 of compacted a
blend of a heavy metal powder, such as tungsten powder, and a
lighter metal powder, such as tin powder, encased within a copper
jacket 66. Alternatively, the projectile may be of any of the
commonly known metals, metal powders, metal alloys, and the
like, which are used in the manufacture of projectiles for rifle
ammunition. In the round of ammunition depicted in Figure 1, the
length of the projectile is such as provides for at least the distal
end 68 of the projectile to project outside the leading end 18 of the
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case, and for the flat proximal face 51 of the proximal end 56 of the
projectile to project inwardly into the interior volume of the case.
As depicted, preferably, the proximal end 56 of the projectile
extends to a location within the case whereby the proximal face 51
of the projectile is disposed immediately adjacent the distal surface
53 of the disc 50, which in turn, is in overlying engagement with
the top surface 52 of the powder charge 38. This positional
relationship of the flat face of the projectile with the disc and
powder charge serves to contain the powder charge within its
desired position within the case and adjacent the primer end of the
case, with no material void spaces within the powder charge.
Thus, the powder charge does not alter its position within the case
irrespective of the orientation of the gun from which the round is
fired.
The ability to employ a longer-than-normal projectile within
the case of a given caliber round of ammunition provides the
ability to employ heavier-than-normal projectiles. This ability to
employ a heavy projectile, along with a "reduced" volume of slow
burning gun powder for a given caliber round of ammunition
permits one to build up, and sustain, the required gas pressure
within the rifle as is necessary to operate the bolt of the rifle when
it is fired in the automatic or semi-automatic mode, in particular.
Of course, single shot firing of an automatic or semi-automatic rifle
is also possible and the ammunition of the present invention will
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also operate the gas-operated bolt of the rifle during such single
shot firing.
In the prior art, it has been taught that if one desires to
manufacture a round of ammunition for a rifle of a given caliber
wherein the projectile of the round is propelled from the rifle at less
than supersonic velocity, reduction of the volume of the gun
powder used, and employing a fast burning gun powder, will serve
this purpose, keeping all other components of the round
unchanged from the supersonic version of the given caliber round.
Aside from the problems stated hereinabove relative to the
movement of the gun powder within the case as a function of the
position of the rifle at the time of its firing (aimed up or down or
horizontal), these prior art efforts have failed to provide for
consistent buildup of the required gas pressure within the rifle for
operation of its gas-operated bolt. This problem in the prior art
lead to the conventional wisdom that subsonic ammunition
requires a fast burning powder. The present inventor has found
that the round of ammunition provided by the present invention
can be made to function with slow burning powder. One suitable
gun powder is Hodgdon H50BMG. The relatively high density
(such as tungsten powder) of the projectile employed by the
present inventor offers such initial resistance, and/or friction and
drag within the barrel of the rifle that the present inventor has
found that a slow burning powder may be employed without
causing the slow burning powder to propel the projectile from the
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rifle barrel at a supersonic velocity. This combination also
functions to build up within the rifle barrel the desired gas
pressure for consistently operating the bolt of the rifle, still without
the projectile being propelled from the barrel at a supersonic
velocity.
In a specific example, rounds of 5.56 mm ammunition were
manufactured employing a commercial case for this caliber
ammunition. Twelve grains of Hodgdon H50BMG gun powder was
loaded into the case which had been fitted with a conventional
primer. A die-cut disc of "target stock" paper of about 0.014 inch
thickness was introduced into the case and overlaid on the
exposed top surface of the powder change. The disc was
compressed about its circumferential margins to about 0.010 inch
thickness. A 150 grain powder-based projectile, 1.24 inches in
length, was introduced into the case to a depth such that the
overall length of the round (from the outermost tip of the projectile
to the bottom end of the case) was not greater than 2.260 inches,
this length being the standard length of a round of 5.56 mm
ammunition which is intended to be fed from a magazine into the
firing chamber of a rifle which accepts this ammunition. In one
embodiment, once the projectile was positioned within the case,
the necked-down portion of the case was crimped, i.e. cannelured,
to retain the projectile in the case preparatory to firing. In this
embodiment, the flat proximal face of the projectile was disposed
within less than 0.10 inch of the top surface of the disc. These
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rounds were fired from a standard M 16M4 military rifle having a
barrel length of 14.5 inches and a 1 in 7 twist. Five shot firing
patterns provided a standard deviation in projectile velocity of less
than 15 fps with no round producing a supersonic firing. In fact,
firing of five hundred rounds of the present ammunition did not
result in a single supersonic excursion. These rounds also
consistently operated the gas-operated bolt of he rifle in both
automatic and semi-automatic modes. Moreover, the accuracy
with which these rounds struck a target placed 100 yards out was
surprisingly better than anticipated. For example, five shot firing
patterns consistently resulted in groupings of 2 1/2 inches with an
extreme spread not greater than 4 inches at 100 yards.
In one alternative embodiment, the projectile employed in
the present invention may be tapered in that the diameter of the
projectile from the ogive to the flat end of the projectile increases.
In one embodiment, the taper, along the length of the projectile, on
a 5.56 mm round ranged from between a diameter of 0.22420 and
0.22430 inch at the proximal end of the projectile to between about
0.22390 and 0.22400 at the location of the transition of the body
portion of the case into the necked-down portion of the case.
Preferably, this tapered projectile is provided with at least one
cannelure 70 within that portion of the length of the projectile
which resides within the necked-down portion of the case. The
indentations of the cannelure, in one embodiment, may be about
0.040 inch in depth. The frictional engagement between the
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radially inwardly bulging edge of the cannelure depression provides
sufficient friction to hold the projectile suspended within the case
without interfering with the performance of the round of
ammunition when fired.
Referring to Figure 2, in a further alternative embodiment,
the inventor has found that the addition of a further disc 80
interposed between the disc 50 and the flat proximal end of the
projectile enhances the stability of the position of the disc 50 and
provides enhanced protection against escape of gun powder
particles between the circumferential edge 82 of the disc 50 and
the interior wall 84 of the case. This further disc may be a second
paper disc, but preferably comprises a disc of non-woven cotton
fibers, such as the loosely bound cotton found in Cotton Rounds,
sold by Sentinel Consumer Products, Mentor, OH as Item 2834, for
cosmetic and baby care. This further disk includes a multiplicity
of tortuous pathways through its thickness and therefore functions
as a filter for the capture of gun powder particles which may
escape past the disc 50. As is true with the paper disc, it is most
desirable that the fibrous material comprising the paper or cotton
disc burn very quickly and with a minimum ash residue. As
currently understood, the weight of cotton fibers making up the
cotton disc preferably is between about 0.10 and 0.16 grains, but
heavier weights of the cotton disc have been employed
successfully.
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In a still further alternative embodiment, (see Figure 4) the
projectile of the present round of ammunition may include a
rebated boattail 90 trailing end such as depicted in Figure 4 and
further be provided with a hollow fast-burning cellolosic material
in the form of a common drinking straw 92 which has one of its
ends frictionally engaging the rebated boattail 90 of the projectile
to extend therefrom to cause its opposite end to engage, or to be in
near proximity to, a disc (or plurality of discs) disposed in overlying
relationship to the top surface of the gun powder charge. By this
means, the trailing end of the projectile may be spaced a
considerable distance away from the discs) while the "straw"
serves to aid in retention of the disc in its overlying position
relative to the gun powder charge. If desired, the rebated boattail
depicted in Figure 4 may be omitted and only the "straw" used to
engage the discs) as depicted in Figure 6. It will be obvious to one
skilled in the art that other forms of a spacer may be employed to
establish and maintain a desired separation between the end of the
projectile and the disc(s).
Whereas the present invention has been described in specific
terms and examples, one skilled in the art will recognize
alternatives. For example, whereas each of the discs 50 and 80
have been described as having opposite planar parallel sides, it will
be recognized that one or more of the sides of the discs may
suitably be concave or convex as the case may be.
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