Note: Descriptions are shown in the official language in which they were submitted.
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SHOTSHELL WITH REDUCED DISPERSION
OF PROJECTILES
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application Serial No. 61/790,025, filed March 15, 2013. The entire disclosure
of
the above-referenced application is incorporated herein.
FIELD
[0002] This disclosure relates to ammunition and in particular, to
shotshell cartridges.
BACKGROUND
[0003] This section provides background information related to the
present disclosure which is not necessarily prior art.
[0004] Shotshells can propel a single projectile, such as a slug,
or
more commonly, multiple projectiles, such as birdshot or buckshot. The
dispersion of multiple shot pellets at a given distance from the muzzle
affords a
greater chance of hitting a moving target than the singular path of a slug.
Thus,
a moderate dispersion rate is desirable for some applications, such as
waterfowl,
upland, and rabbit hunting where the intended target is moving. However, in
some applications, such as turkey hunting, the intended target is a relatively
motionless and small. In these types of applications, it can be desirable to
have
a tighter pattern, with less shot dispersion.
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[0005] The rate of dispersion of multiple projectile loads can be
influenced by gun systems and cartridge design. Tighter constrictions or
"choke"
in the muzzle section of the barrel can reduce the dispersion rate of shot
pellets
to some degree. Cartridge design elements, such as shot type, wad type, and
buffering can also reduce dispersion rate.
[0006] Lead was the material of choice for early cartridges because
of its density, relative low cost, and easy formability. The easy formability
however was also a negative. Soft lead pellets are deformed when subjected to
the high acceleration forces of cartridge ignition and with direct barrel
contact
while being accelerated toward the muzzle. Early cartridges did not
incorporate
any wad systems. Soft lead shot had direct contact with the barrel. This
resulted
in a considerable dispersion rate. Eventually wads and shot cups provided a
liner or barrier between the shot and barrel to reduce pellet deformation
associated with bore contact. U.S. Patent No. 3,092,026, incorporated
granulated particles intermixed in the shot column to "buffer" the pellets
during
acceleration to reduce deformation further. These feature elements reduced
dispersion rate. Alternate shot materials, such as steel or tungsten, maintain
spherical shape to reduce dispersion, but have other shortcomings, such as low
density or extremely high cost.
SUMMARY
[0007] Embodiments of this invention provide a buffering system to
reduce or eliminate shot pellet deformation during acceleration at ignition,
and
preferably enhance pattern performance. The granulated/particulate buffers
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intermixed in the shot column, as described above, often do not effectively
occupy all the space between shot pellets, and thus, still allow some pellet
deformation. According to a preferred embodiment of this invention, the shot
pellets, or a significant portion of the shot pellets, are substantially
completely
surrounded by a hard, brittle matrix that provides conformal support of the
pellets
during cartridge ignition. The matrix preferably substantially completely
separates from the shot column a short distance after muzzle exit without
significant adherence to the pellets.
[0008] U.S.
Patent No. 34,806 discloses filling pellet interstices with
some melted substances, such as grease, wax, or low melt metallic alloys for
the
purpose of creating a fixed shot charge between two wads. Wax or grease is not
sufficiently hard or brittle to buffer the shot, particularly at the
temperatures
encountered in shotshells, and is unlikely to satisfy the requirements noted.
Low
melt metallic alloys would be costly and could add significant parasitic
weight to
the cartridge payload. U.S. Patent No. 3,422,761 discloses embedding shot
pellets in a matrix of polyurethane foam. However, the very nature of foam
products creates the undesired air gaps in the shot column that is undesirable
for
a buffering system. Air gaps in foam can collapse upon ignition and result in
significant pellet deformation. U.S. Patent Nos. 4,913,054 and 6,367,388
disclose methods of embedding or containing multiple projectiles as a single
projectile until impact with a target. U.S. Patent No. 4,733,611 discloses
shot
pellets embedded in a wax/Styrofoam matrix, but as described above, a wax-
based matrix can be unsatisfactory for buffering.
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[0009] Embodiments of this invention can provide a buffering
system for multi-projectile shot cartridges which provides conformal support
to
individual pellets to reduce or eliminate pellet deformation. Embodiments of
this
invention can provide a buffering system for multi-projectile shot cartridges
which
reduces dispersion rate of the shot pellets after exiting the gun barrel. Some
embodiments are capable of meeting or exceeding the pattern performance of
tungsten-based shot loads at a considerably lower cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Fig. 1 is a cross-section of a preferred embodiment of a
shotshell cartridge constructed, according to the principles of this
invention;
[0011] Fig. 2 is a cross-section of an alternate construction of
the
preferred embodiment of a shotshell cartridge constructed, according to the
principles of this invention; and
[0012] Fig. 3 is a cross-section of a second alternate construction
of
the preferred embodiment of a shotshell cartridge constructed, according to
the
principles of this invention.
DETAILED DESCRIPTION
[0013] Example embodiments will now be described more fully with
reference to the accompanying drawings.
[0014] A preferred embodiment of a shotshell in accordance with
the principles of this invention is indicated generally as 20 in Fig. 1. The
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shotshell 20 is generally of the type having a hull 22, with a head 24 at the
proximal end of the hull. A charge of propellant 26 is disposed in the hull
22. A
wad 28 is disposed in the hull 22 distal to the propellant 26. A load 30 is
disposed in the hull 22 distal to the wad 28. The load 30 includes a plurality
of
individual shot or pellets 32, at least a portion of which are at least
partially
surrounded by a friable polymeric material 34 forming a matrix 36 that breaks
up
upon the firing of the shell to release to the shot.
[0015] The hull 22 is preferably a conventional hull made of a
polymeric material. The head 24 is preferably made of brass, but it could be
made of some other material. The propellant 26 can be any conventional
propellant. The wad 28 preferably includes a gas sealing cup wad 38, a
ballistic
cushion section 40, and a cup section 42 to house the shot or pellets 32.
[0016] The shot or pellets 32 can be conventional round shot of any
desired size from birdshot sizes to buckshot sizes. The shot or pellets 32 can
be
other shapes and sizes, as well. The shot or pellets 32 can be made of lead or
lead alloy or other suitable material, including copper, tungsten, bismuth, or
steel.
[0017] At least the proximal-most shot or pellets 32 are at least
partially surrounded by friable polymeric material 34 (Fig. 3). More
preferably,
about half of the shot or pellets 32 are at least partially surrounded by
friable
polymeric material 24 (Fig. 2), and most preferably, substantially all of the
pellets
are at least partially surrounded by friable polymeric material (Fig. 1).
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[0018] The friable polymeric material 34 is preferably a
polyurethane. An example of a suitable material is Smash! Plastic . The
friable
polymeric material preferably has a hardness of greater than about 80 (Shore
D).
[0019] Preferably, the matrix 36 in the form of a liquid, is
dispensed
in the cup section, followed by a charge of shot pellets. Alternatively, the
shot
pellets can be introduced first, followed by the matrix in liquid form, or the
shot
pellets and matrix in the form of a liquid can be mixed and introduced
together.
In a preferred embodiment, the pellets are pre-coated with a release agent,
such
as a mold release for example, Universal Mold Release agent, available from
Smooth-On, Inc., 2000 Saint John Street, Easton PA 18042, to reduce bonding
between the matrix and the pellets. The matrix material is preferably a two-
part
polyurethane resin, such as Smash! Plastic , available from Smooth-On, Inc.,
2000 Saint John Street, Easton PA 18042 or similar material with similar
properties. Smash! Plastic has a mixed viscosity of about 900 cps, a cured
specific gravity of about 1.036 g/cc, and a hardness of about 80 (Shore D).
Smash! Plastic is prepared by mixing equal amounts of two components, Part
A, a modified aliphatic diisocyanate, containing Dicyclohexylmethane-4,
4'diisocyanate, and Part B, a resin.
[0020] Accurately dispensing a two-part resin can be
accomplished with a unit, such as the Bartec B1000, a gear pump metered
dispenser.
[0021] By introducing the pellets after the liquid matrix, the
pellets
settle into the liquid matrix, providing a shot column with all spaces between
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pellets substantially and completely filled by the matrix material. The
viscosity
and gel time of the resin, permit pellets to fall through the resin, yet
resist resin
flowing past the cushion wad or powder cup into powder column. A folded tube
crimp or top wad and roll crimp provide closure of the cartridge. In one
preferred
embodiment, the closure includes a frangible top wad. A properly fitted top
wad
and roll crimp prevents leakage of matrix material during cure/set to allow
immediate packing of cartridges.
[0022] After an appropriate cure cycle, the liquid matrix becomes a
hard, brittle solid. Upon cartridge ignition and load acceleration, the solid
matrix
breaks into small particles and travels down the barrel, still occupying the
space
between individual pellets. At muzzle exit, the shot cup petals deploy and the
small matrix particles begin to separate from the shot column. During launch,
the
hard matrix provides conformal support to individual pellets to reduce, and
preferably substantially eliminate pellet deformation. During separation near
muzzle exit, the particles can provide a temporary windshield effect, further
improving pattern performance.
[0023] In another embodiment of the present invention, shot cups,
shot, and matrix are pre-assembled and cured ahead of subsequent loading in
the cartridge. The pre-assembled and cured shot cups with the shot in a
hardened matrix can be loaded into the hull.
Example 1
[0024] Exemplary shotshell cartridges constructed in accordance
with a preferred embodiment of the present invention, were tested against two
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commercially available shotshell cartridges designed to have tight patterns
for
turkey hunting applications.
A) Winchester product symbol STH1236, 12 gauge 3" 1-3/4oz Copper
Plated #6 lead shot, with PE particles for shot buffering.
B) Winchester product symbol STXS1236, 12 gauge 3" 1-3/4oz
Tungsten-based #6 shot, with polystyrene particles for shot buffering.
C) Exemplary cartridges in accordance with the preferred embodiment
of this invention, 12 gauge 3" 1-3/4oz Copper plated #6 lead shot, with 4
grams of Smash! Plastic polyurethane resin and pellets pre-coated with
Universal Mold Release spray.
[0025] All
three samples utilize similar wad systems involving a gas
sealing powder cup, ballistic cushion member, and a 4 petal shot cup. All
samples were fired in a Remington 870 shotgun with a Rhino .660 choke tube.
Percentages shown, are ratio of pellets in the target area to total pellets in
the
cartridge, and are an average of ten cartridge patterns each. High pattern
percentages equate to reduced pellet dispersion. The results are shown in
Table
1.
Table 1
Sample Distance 10" Circle 20" Circle 30" Circle
A 40 yards 22% 55% 81%
B 40 yards 32% 73% 92%
C 40 yards 48% 84% 95%
A 60 yards 8% 21% 39%
B 60 yards 12% 32% 56%
C 60 yards 21% 53% 78%
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[0026] The data in Table 1 shows the exemplary cartridges (C) had
twice the performance of standard lead shot turkey load in most trials (A),
and
exceeded tungsten-based shot loads (B) in all the trials.
Example 2
[0027] Exemplary shotshell cartridges constructed in accordance
with a preferred embodiment of the present invention, were tested against
alternate matrix materials identified in previous patents. The cartridges are
assembled in similar fashion with the exception of the matrix material. Mold
release was not used on samples B, C, or D since the respective patents did
not
disclose use of such coatings on pellets.
A) Subject inventive cartridges, 12 gauge 3" 1-3/4oz Copper plated #6
lead shot, with 4 grams of Smash! Plastic polyurethane resin and pellets pre-
coated with Universal Mold Release spray.
B) Same as above except use of paraffin wax as matrix, per U.S.
Patent No. 34,806.
C) Same as above except use of polyurethane foam as matrix, per
U.S. Patent No. 3,422,761. Great Stuff polyurethane foam by DOW was
selected for this trial.
D) Same as above, except use of Epic resin Cytec RN1000 epoxy
resin with a hardener of EA-02 as matrix.
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Table 2
Sample Distance 20" Circle 30" Circle
A 60 yards 55% 78%
B 60 yards 10% 22%
C 60 yards 9% 21%
D 60 yards Slug* Slug*
*this matrix did not break up or fracture at cartridge ignition, and traveled
to target as single projectile.
[0028] As seen in the table above, properties of the inventive
cartridge provides differentiation and enhanced pattern performance over prior
art.
[0029] The foregoing description of the embodiments has been
provided for purposes of illustration and description. It is not intended to
be
exhaustive or to limit the disclosure. Individual elements or features of a
particular embodiment are generally not limited to that particular embodiment,
but, where applicable, are interchangeable and can be used in a selected
embodiment, even if not specifically shown or described. The same may also be
varied in many ways. Such variations are not to be regarded as a departure
from
the disclosure, and all such modifications are intended to be included within
the
scope of the disclosure.
