U.S. patent number 3,797,396 [Application Number 05/234,731] was granted by the patent office on 1974-03-19 for reinforced lightweight cartridge.
This patent grant is currently assigned to The United States of America as represented by the Secretary of the Army. Invention is credited to Frederick P. Reed.
United States Patent |
3,797,396 |
Reed |
March 19, 1974 |
REINFORCED LIGHTWEIGHT CARTRIDGE
Abstract
The firing obturation of lightweight military cartridges
fabricated from a aterial other than brass can be considerably
improved by the inclusion of a thin-walled cup in the head portion
of the case prior to forming the required exterior taper thereof.
Since the cup is fabricated from a more deformable material than
that of the case, the tapering of the latter produces radial
recovery forces in the mouth of the cup which serve to increase the
total pressure imparted to the cartridge case sidewalls by the
pressures generated during the firing of the cartridge thereby
accelerating the obturation of the case in the firing chamber to a
greater degree along the portion coextensive with the cup mouth
than along the remainder of the case.
Inventors: |
Reed; Frederick P. (Davenport,
IA) |
Assignee: |
The United States of America as
represented by the Secretary of the Army (Washington,
DC)
|
Family
ID: |
22882565 |
Appl.
No.: |
05/234,731 |
Filed: |
March 15, 1972 |
Current U.S.
Class: |
102/468;
102/464 |
Current CPC
Class: |
F42B
5/285 (20130101) |
Current International
Class: |
F42B
5/00 (20060101); F42B 5/285 (20060101); F42b
005/28 (); F42b 005/30 () |
Field of
Search: |
;102/43R,43P,44,38,42R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Stahl; Robert F.
Attorney, Agent or Firm: Kelly; Edward J. Berl; Herbert
Arnold, Jr.; Albert E.
Claims
I claim:
1. In a firearm cartridge having a forwardly tapered case of a
material other than brass adapted to expand into obturating contact
with the interior walls of a firing chamber in response to the gas
pressures generated during the firing of the cartridge, the
improvement of,
a substantially cylindrical reinforcing cup of a more deformable
material than that of said case and disposed within the rearward
half thereof, said cup having the exterior periphery thereof in
forwardly increasing compressive engagement with the forwardly
tapered interior surface of said case to form an interference fit
therebetween, said cup also having forwardly increasing radial
recovery forces therein which approach a maximum at the forward end
thereof to impart corresponding obturating expansion to the portion
of said case coextensive with said cup.
2. The cartridge structure defined in claim 1 wherein said case is
formed of steel and said cup is formed of brass.
3. The cartridge structure defined in claim 1 wherein said case is
formed of a heat treated aluminum alloy and said cup is formed of a
more ductile untreated aluminum alloy.
4. The catridge structure defined in claim 1 wherein said case is
formed of aluminum and said cup is formed of a thermosetting
resin.
5. The cartridge structure defined in claim 1 wherein said
reinforcing cup is formed with an open end of slightly larger
diameter than the opposite closed end thereof to induce a maximum
amount of recovery forces therein subsequent to the forming of the
forward taper required by the case.
6. In a firearm cartridge having a case of deformable material
other than brass adapted to expand into obturating contact with the
interior wall surface of a firing chamber in response to the
pressures generated during the firing of the cartridge, said case
comprising,
a head,
a hollow body extending forwardly from said head to define a
forwardly tapered interior, and
a reinforcing cup of a more deformable material than that of said
case disposed within the rearward half of said body and having an
original exterior periphery of greater diameter than the
corresponding interior diameter of said hollow body prior to the
tapering thereof to define an interference fit therebetween, said
cup also having radial recovery forces therein increasing forwardly
along the length thereof to impart a maximum rapidity of obturating
expansion to said case in the vicinity of the forward end of said
cup.
7. The cartridge defined in claim 6 wherein said head and said body
of said case are formed of aluminum and said cup is formed of a
thermosetting epoxy resin of sufficient thickness and resiliency to
obturate any rupture which may occur within the portion of said
body contiguous with said cup during the firing of the cartridge.
Description
BACKGROUND OF THE INVENTION
This invention relates to small arms ammunition and is more
particularly directed to tapered cartridge cases fabricated of
materials other than the customary brass.
The constantly increasing scarcity and cost of copper as well as
the need for a reduction in the weight of conventional brass
cartridges has led to their manufacture from such diverse materials
as molded plastics, aluminum, or steel. While these efforts to
provide an adequate substitute for brass have met with varying
degrees of success in ammunition designed for use in sporting arms,
such has not been the case in military firearms designed to fire
high pressure cartridges at relatively high rates of sustained
fire. For example, where the cartridge cases are fabricated from
aluminum and are joined by steel links into a continuous
articulated belt, the exit of the ammunition from the magazine and
the delinking action required during the feeding thereof into the
firing chamber of the gun frequently results in considerable
scratching and nicking of the exterior surfaces of the cases. Since
the wall thickness of aluminum cases is often as low as 0.010
inches, any visible scratch or other indentation generally produces
a weakened area which is unusually prone to rupture or
"burn-through" during the expansion imparted to the case by the
relatively high pressures and hot gases generated upon the firing
of the cartridge. In the event the break in the cartridge case
occurs prior to completion of the normal obturating contact thereof
with the interior wall surface of the firing chamber, the
consequent escape of the hot and corrosive discharge gases produces
an extremely rapid erosion of the firing chamber, the face of the
firearm bolt and the tip of the firing pin. Obviously, any
deterioration in the ability of the closed firearm breech to seal
against the escape of the discharge gases during the period of peak
pressure is extremely dangerous to the operator of the firearm.
Other difficulties encountered in the use of cartridges fabricated
from materials of lighter weight than brass are the lack of
adequate strength in the head portion of the cartridge case and the
cartridge feeding and delinking problems caused by the fact that,
contrary to conventional cartridges with brass cases, the
projectile portion is significantly heavier than the case portion
thereof, thereby causing the center of gravity of the total round
to be unfavorably located more forwardly in the cartridge.
SUMMARY OF INVENTION
Accordingly, it is an object of this invention to provide an
improved cartridge for firearms wherein the base or head portion of
the case is internally reinforced by a separate insert fabricated
from a material having greater deformability qualities than the
material utilized for the case.
Another object of the present invention resides in the provision of
a cartridge as aforesaid wherein the internal reinforcing means
serves to improve the rapidity with which the rear or head portion
of the case will expand into obturating contact with the interior
wall surfaces of the firing chamber.
Still another object of this invention is to provide a reinforcing
means for a cartridge which is capable of accelerating the
expansion of the contingent portion of the cartridge case to
minimize the rearward escape of high pressure gases in the event of
any rupture or burn-through in the walls of the cartridge case.
An important object of this invention resides in the provision of a
reinforcing means in the rear end of a cartridge case in a manner
which will insure maximum rapidity of obturation in the firing
chamber of a gun along the portion of the case coextensive with the
forward portion of the reinforcing means.
It is an additional object of this invention to provide a cartridge
wherein the aforesaid internal reinforcement of the case portion is
also utilized to compensate for the forward relocation of the
center of gravity which would otherwise have resulted from the use
of a lighter material than brass for the cartridge case.
It has been found that the foregoing objects can be readily
accomplished in forwardly tapered cartridges intended for military
use by providing a thin-walled cup within the head portion of the
cartridge case. Such cup is fabricated from a more deformable
material than that of the case and is arranged to extend forwardly
beyond the origination of the tapered portion of the case and
terminate within the rearward half thereof. The taper required by
the case is imparted thereto after the cup has been inserted in
place so that the resulting reduction in the diameter of the cup
mouth induces built-in radial recovery forces therein which serve
to increase the total pressure imparted to the cartridge case
sidewalls by the gases generated during the firing of the
cartridge. As a result, that portion of the cartridge case which is
coextensive with the mouth of the cup is peripherally preloaded to
such an extent that the time period required to achieve positive
obturation of the firing chamber in which the cartridge is fired is
significantly reduced. Thus, in the event of any rupture or other
perforation of the cartridge case wall forwardly of the cup, the
deleterious erosion of the bolt face and firing pin tip ordinarily
caused by the premature release of the discharge gases is
substantially diminished. In addition, the added mass of the cup
effectively compensates for the substantial forward relocation of
the center of gravity of the entire cartridge which would have
otherwise taken place as a result of the decreased weight obtained
in the case by the fabrication thereof from a material lighter than
brass.
BRIEF DESCRIPTION OF THE DRAWINGS
The exact nature of the invention as well as other objects and
advantages thereof will be readily apparent from consideration of
the following specification relating to the annexed drawings
wherein:
FIG. 1 is a centrally broken longitudinal section of a typical
lightweight military cartridge with a forwardly tapered case
containing the reinforcing cup of the present invention, the
stressed area produced by the final forming of the case being
located between arrows A and B;
FIG. 2 is a fragmentary view of the rearward portion of the
cartridge of FIG. 1 and is enlarged to show the relationship of the
reinforcing cup to the interior of the case prior to the final
forming of the latter;
FIG. 3 is a central longitudinal section of the rearward portion of
the cartridge of FIG. 1 taken immediately following the discharge
thereof in the firing chamber of a gun to show, in somewhat
exaggerated fashion, the initial obturation achieved during the
firing thereof; and
FIG. 4 is a sectional view taken along line 4--4 in FIG. 3 showing
the additional obturation provided by the reinforcing cup in the
event of any perforation in the corresponding portion of the
cartridge case sidewall.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As best shown in FIG. 1, the type of military cartridge to which
the present invention is particularly adapted generally consists of
an elongated case 12 which is forwardly tapered from a point
beginning with the annular extractor groove 14 provided in the base
or head portion 16 to the start of necked portion 18 formed at the
forward end thereof. While such taper is, of course, dependent on
the caliber of the cartridge, a decrease in diameter of as small as
0.002 inches per inch of length has been found to be adequate in
accomplishing the purposes of this invention. The sidewalls of case
12 are generally formed with a forwardly decreasing wall thickness
which, in an aluminum cartridge, may reach a minimum of 0.010
inches at the junction with neck portion 18.
A forwardly opening cup 20 of a more deformable material than that
of cartridge case 12 is arranged to be seated within the rearward
half thereof so as to bottom against the forward face 21 of head
portion 16. Cup 20 is dimensioned to slidably fit into case 12 and
be seated against face 21 prior to the forming operation which
imparts the required taper thereto. While cup 20 may be cylindrical
in shape, the sidewalls thereof are preferably formed to terminate
in a larger diameter at the open end 22 thereof than at the rear
end thereof. Furthermore, the walls of cup 20 are relatively
thinner than the cross-section of case 12. Thus, when the tapering
of cartridge case 12 is completed, the forward or open mouth end 22
of cup 20 is radially compressed into an interference fit with case
12, thereby inducing radial recovery forces which act on the
interior wall surfaces of case 12 to create a peripheral
prestressed area along the portion defined by arrows A and B in
FIG. 1. The bottom of cup 20 is provided with a central opening 26
therethrough communicating with the primer hole 28 in cartridge
case head portion 16.
Upon the firing of the cartridge in the chamber 30 of a firearm
barrel 31, the prestressed area between arrows A and B will respond
more rapidly than the adjacent areas of case 12 to the pressure of
the discharge gases generated within the interior thereof. As a
result, the portion of the cartridge case sidewall adjacent end 22
of cup 20 will expand annularly, as best indicated at 32 in FIG. 3,
into obturating contact with the corresponding interior wall
surface of firing chamber 30. In addition, the firing pressures
within cup 20 impart a slight degree of set-back thereto thereby
exerting a wedging action on the sidewalls of case 12 which serves
to increase the longitudinal extent of the annular expansion
thereof.
Thus, a cartridge case constructed in accordance with the foregoing
description will provide a significantly faster obturation of the
firing chamber when a cartridge is fired therein than a
conventional brass cartridge case with no internal reinforcement.
As will hereinafter be explained, this is an extremely important
factor where the cartridge case is fabricated from a lighter and
weaker material than brass or is provided with a substantially
thinner sidewall than a standard brass case. In either situation,
it has been found that the feeding of ordinary cartridges into a
firearm with sufficient capacity to achieve a sustained high rate
of fire frequently produces noticeable scratches and nicks in the
sidewalls of the cases. Even deeper scratches are often produced
during the removal of the metal links ordinarily employed to retain
the cartridges in a continuous articulated belt. As a result, the
relatively thin sidewalls of these lightweight cases are unusually
prone to rupture under the high pressures and resulting expansion
imparted thereto during the discharge of military type cartridges.
Furthermore, even if the wall of the cartridge case should possess
sufficient strength to resist splitting or rupture, it has been
found that the temperatures attained by the discharge gases combine
with the high pressures involved to actually burn through any area
weakened by a physical imperfection, especially in aluminum cases
where the metal actually acts as a fuel thereby increasing the
likelihood of any such burn-through.
In the event rupture or burn-through of the existing types of
cartridge cases occurs before obturation of the firing chamber has
been fully completed, the hot discharge gases will flow between the
exterior of cartridge case 12 and the interior wall surface of
firing chamber 30 into corrosive contact with the face of the
firearm bolt and the tip of the firing pin. It has been found that
as few as two occurrences of this gas escape will erode the firearm
components to an unsafe degree. This is particularly true where the
break in the wall of the cartridge case occurs at a point within
the rear one-quarter of the overall length thereof.
However, the problem of inadequate obturation of the firing chamber
in the event of a premature escape of the discharge gases can be
successfully overcome by the reinforcing cup of the present
invention installed in accordance with the technique described
above. In order to achieve optimum results, it is essential that
the cartridge case and cup be selected from materials such that the
cup will respond more readily to diametrical expansion than the
case. By way of example, where the cartridge case is fabricated
from one of the materials listed in Column A, the reinforcing cup
could be fabricated from the material specified in the same line of
Column B.
a b cartridge Case Material Reinforcing Cup Material steel brass
heat treated aluminum alloy untreated aluminum alloy aluminum epoxy
resin
These and like combinations of materials will ensure the maximum
degree of expansion of cartridge case 12 at the area adjacent mouth
22 of cup 20. Furthermore, if a break or split in the cartridge
case sidewall, as indicated by the arrow in FIG. 4, occurs
rearwardly of the mouth of cup 20, the more deformable material of
the latter is actually extruded into the break, as shown at 34, to
thereby seal the interior of case 12 prior to obturating contact
thereof with the wall of firing chamber 30.
In addition to the foregoing, the reinforcing cup 20 also
strengthens head portion 16 of case 12. This is particularly
important in the base portion of case 12, which is frequently only
partially supported by the walls of the firing chamber 30, since it
permits a corresponding reduction in the thickness of case 12
thereby effecting a desirable decrease in the total weight of the
cartridge. The reinforcement function of cup 20 also permits a
desirable relaxation of the limitations ordinarily imposed on the
length and depth of the various machining cuts included in the rear
portion of firing chamber 30 to provide the necessary extractor and
ejector grooves, feed ramps, chamfers or other projectile guide
surfaces.
The foregoing disclosure and description of the invention is
illustrative only. Various changes may be made within the scope of
the appended claims without departing from the spirit of the
invention.
* * * * *