U.S. patent application number 11/642050 was filed with the patent office on 2011-04-21 for jacketed boat-tail bullet.
This patent application is currently assigned to Olin Corporation. Invention is credited to Gerald Todd Eberhart.
Application Number | 20110088537 11/642050 |
Document ID | / |
Family ID | 36060345 |
Filed Date | 2011-04-21 |
United States Patent
Application |
20110088537 |
Kind Code |
A1 |
Eberhart; Gerald Todd |
April 21, 2011 |
JACKETED BOAT-TAIL BULLET
Abstract
A bullet includes at least a mid core and a rear core in tandem
alignment. The hardness of the mid core is greater than the
hardness of the rear core. A jacket envelops both the mid core and
the rear core. The jacket has a generally cylindrical sidewall,
which is in contact with the mid core, and a boat-tail, which is in
contact with the rear core. The rear core is substantially
contained within the boat-tail. The mid core and the rear core may
be substantially lead-free. In one embodiment, the bullet includes
a front core in tandem alignment with the rear core and in contact
with a nose portion of the jacket. In another embodiment, the mid
core extends from the nose portion of the bullet to the
boat-tail.
Inventors: |
Eberhart; Gerald Todd;
(Bethalto, IL) |
Assignee: |
Olin Corporation
|
Family ID: |
36060345 |
Appl. No.: |
11/642050 |
Filed: |
December 19, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10832082 |
Apr 26, 2004 |
7150233 |
|
|
11642050 |
|
|
|
|
Current U.S.
Class: |
86/55 |
Current CPC
Class: |
F42B 12/78 20130101;
F42B 12/74 20130101 |
Class at
Publication: |
86/55 |
International
Class: |
F42B 30/02 20060101
F42B030/02 |
Claims
1-17. (canceled)
18. A method for making a bullet, the method comprising: forming a
jacket precursor to include: a nose portion, and a generally
cylindrical sidewall extending from the nose portion, the nose
portion and the generally cylindrical sidewall defining a cavity;
depositing at least a one-piece mid core that includes a
substantially monolithic, non-tubular construction within the
cavity; depositing a rear core within the cavity in tandem
alignment with the mid core and positioned proximate a rear portion
of the cylindrical sidewall, the rear core having a hardness less
than the hardness of the mid core; and angularly indenting the rear
position of the cylindrical sidewall and the rear core to form a
boat-tail, wherein after the indenting, the rear core substantially
fills the boat-tail.
19. The method of claim 18, wherein the mid core and the rear core
are substantially lead-free.
20. The method of claim 18, wherein after the indenting, the mid
core extends from the nose portion to the boat-tail.
21. (canceled)
22. The method of claim 18, further comprising: depositing a front
core within the cavity in tandem alignment with the mid core, the
front core being positioned adjacent to the nose portion.
23. The method of claim 22, wherein the front core is formed from
steel.
24. The method of claim 18, wherein the mid core is formed from: a
high-density constituent material selected from the group of
tungsten, tungsten carbide, carballoy, and ferro-tungsten; and a
second, lower density constituent consisting of either a metallic
matrix material or a plastic matrix material.
25. The method of claim 24, wherein the metallic matrix material is
selected from the group consisting of: tin, zinc, iron, copper, and
mixtures or alloys of one or more of the foregoing.
26. The method of claim 24, wherein the plastic matrix material is
selected from the group consisting of: phenolics, epoxies,
dialphthalates, acrylics, polystyrenes, polyethylene, or
polyurethanes.
27. The method of claim 18, wherein the mid core is formed from one
of: copper, bismuth, tin, gold, silver, pewter, bronze and mixtures
or alloys including one or more of the foregoing.
28. The method of claim 18, wherein the mid core is formed from an
organic polymer filled with a metal.
29. The method of claim 18, wherein the rear core has a Brinell
hardness less than about 50.
30. The method of claim 29, wherein the rear core is formed from
tin or a tin base alloy.
31. The method of claim 29, wherein the rear core is formed from
one of: copper, zinc, tin, and mixtures or alloys including one or
more of the foregoing.
32. The method of claim 20, wherein the mid core has a weight of
about 38 grains and is formed from: a high-density constituent
material selected from the group of tungsten, tungsten carbide,
carballoy, and ferro-tungsten, and a second, lower-density
constituent consisting of either a metallic matrix material or a
plastic matrix material; and wherein the rear core has a weight of
about 4.3 grains and is formed from tin or a tin base alloy.
33. The method of claim 23, wherein the mid core has a weight of
about 30 grains and is formed from: a high-density constituent
material selected from the group of tungsten, tungsten carbide,
carballoy, and ferro-tungsten, and a second, lower-density
constituent consisting of either a metallic matrix material or a
plastic matrix material; and wherein the rear core has a weight of
about 4.3 grains and is formed from tin or a tin base alloy.
34. The method of claim 18, wherein a transition point between the
generally cylindrical sidewall and the boat-tail is formed by a
rebate in the generally cylindrical sidewall.
35. The method of claim 18 wherein the rear core is inserted into
the jacket in the form of a sphere.
36. A method for making a bullet, the method comprising: forming a
jacket precursor to include: a nose portion, and a generally
cylindrical sidewall extending from the nose portion, the nose
portion and the generally cylindrical sidewall defining a cavity;
depositing at least one forward core of substantially monolithic,
non-tubular construction and a rear core into the cavity, the rear
core being in tandem alignment with the at least one forward core
and positioned proximate a rear portion of the cylindrical
sidewall, the rear core having a hardness less than the hardness of
the at least one forward core; and angularly indenting the rear
position of the cylindrical sidewall and the rear core to form a
boat-tail, wherein after the indenting, the rear core substantially
fills the boat-tail.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to small arms ammunition and, more
particularly, to jacketed, boat-tailed bullets.
[0003] 2. Description of the Related Art
[0004] Jacketed bullets include a layer of metal, called a jacket,
surrounding at least a portion of a core of the bullet. The core is
typically made of lead. It is well known that the heel of a
jacketed bullet may be tapered to form what is known as a boat-tail
(BT), which acts to enhance the bullet's ballistic stability and to
improve the bullet's aerodynamic performance.
[0005] Examples of jacketed, boat-tailed bullets can be found in
small caliber, 0.5 inch and under, penetrator projectiles used by
military forces worldwide. For example, the United States and NATO
military forces use vast quantities of M855 cartridges containing
62 grain penetrator bullets, one of which is depicted generally at
10 in FIG. 1. As shown in FIG. 1, the M855 bullet 10 has two
aligned cores 12 and 14 enveloped by a brass jacket 16. A steel
core 12 is located in a nose section 18 of the bullet 10 and a 32
grain lead core 14 is swaged into a rear section 20. The bullet 10
has a heel that is tapered to form a boat-tail 22, which provides
the bullet 10 with ballistic stability and improved aerodynamic
performance. In this case, the boat-tail 22 extends from a bearing
surface 24 of the bullet 10 to a base 26 of the bullet 10. At a
total weight of 62 grains, the M855 bullet 10 has the kinetic
energy required to penetrate a 10 gage steel plate when fired from
a distance of 600 meters.
[0006] In the M885 bullet 10, the steel front core 12 is used to
provide the integrity necessary to promote penetration against
light armored targets. The lead rear core 14 allows the projectile
weight to be obtained using the lowest cost heavy metal available.
In addition, the malleable lead material can be conveniently
compacted inside the bullet jacket 16 to form a true, cylindrical
bearing surface CD 24 diameter, while producing a consistent form
and closure of the boat-tail 22 of the bullet 10. It is this
boat-tail 22 forming operation and heel closure that has a
significant impact on improving the projectile's stability during
launch and, therefore, the accuracy of the bullet 10.
[0007] Many of these penetrator rounds are expended at target
ranges in military drills. The large volume of lead contained
within the projectiles makes environmental reclamation of the
target ranges difficult and expensive. Accordingly, various
attempts have been made to produce effective lead-free bullets.
[0008] For example, U.S. Pat. No. 5,399,187 to Mravic, et a. is
directed to lead-free bullets having a density similar to that of
lead. The lead-free bullets comprise a compacted composite
containing a high-density first constituent selected from the group
consisting of tungsten, tungsten carbide, ferro-tungsten and
mixtures thereof; and a lower density second constituent selected
from the group consisting of tin, zinc, aluminum, iron, copper,
bismuth, and mixtures thereof, wherein the density of the lead-free
bullet is in excess of 9 grams per cubic centimeter and the
lead-free bullet deforms or disintegrates at a stress of less than
about 45,000 psi. U.S. Pat. No. 5,399,187 is incorporated by
reference herein in its entirety.
[0009] In another example, U.S. Pat. No. 6,112,669 to Mravic, et
al. is directed to a lead-free projectile made from a composition
containing about 5-25% by weight tungsten and more than about 97%
by weight tungsten plus iron. U.S. Pat. No. 6,112,669 is
incorporated by reference herein in its entirety.
[0010] In yet another example, U.S. Pat. No. 6,085,661 to
Halverson, et al. discloses a small caliber non-toxic penetrator
projectile that has a first core and a second core tandemly aligned
and enveloped by a jacket. The first core has a hardness greater
than the hardness of the second core, which has a Brinell hardness
of between about 20 and about 50. The hardness of the second core
is significantly higher than the hardness of lead, and when the
first core strikes a target, the second core resists compressive
bulging. As a result, more kinetic energy is transferred to the
first core rather than being diffused along the surfaces of an
armored target. U.S. Pat. No. 6,085,661 is incorporated by
reference herein in its entirety.
[0011] While various non-toxic metals have proven to be successful
replacements for lead in the manufacture of bullets, these
non-toxic metals are not without their shortcomings. For example,
many non-toxic metals have a hardness greater than lead, which
makes the non-toxic metal more difficult to form in the bullet
manufacturing process. Where the bullet is to be formed with a
boat-tail, excessive material hardness make the mechanical swaging
processes utilized in standard bullet manufacture ineffective to
form the boat-tail. The boat-tail must then be cut or ground into
the rear of the core and, during mechanical enveloping of the
jacket around the excessively hard core, there is limited impinging
of the jacket with the core. The result is a gap between the jacket
and the boat-tail. When this projectile is fired, propellant gasses
are forced between the interface of the jacket and the core causing
distortion of the jacket and resulting in loss of accuracy and
stability. Thus, a new approach is needed to obtain a bullet that
is completely devoid of lead while performing ballistically
similarly to lead with the manufacturing advantages of lead.
BRIEF SUMMARY OF THE INVENTION
[0012] The above-described drawbacks and deficiencies of the prior
art are overcome or alleviated by a bullet including at least a mid
core and a rear core in tandem alignment, with the hardness of the
mid core being greater than the hardness of the rear core. A jacket
envelops both the mid core and the rear core. The jacket has a
generally cylindrical sidewall, which is in contact with the mid
core, and a boat-tail, which is in contact with the rear core. The
rear core is substantially contained within the boat-tail. The mid
core and the rear core may be substantially lead-free. In one
embodiment, the bullet includes a front core in tandem alignment
with the mid core and in contact with a nose portion of the jacket.
The rear core may substantially fill the boat-tail. In various
embodiments, a transition point between the generally cylindrical
sidewall and the boat-tail may be formed by a rebate in the
generally cylindrical sidewall.
[0013] In various embodiments, the mid core is formed from a
high-density constituent material selected from the group of
tungsten, tungsten carbide, carballoy, and ferro-tungsten; and a
second, lower-density constituent consisting of either a metallic
matrix material or a plastic matrix material. The metallic matrix
material may be selected from the group consisting of: tin, zinc,
iron, copper, and mixtures or alloys of one or more of the
foregoing. The plastic matrix material may be selected from the
group consisting of phenolics, epoxies, dialphthalates, acrylics,
polystyrenes, polyethylene, or polyurethanes. Alternatively, the
mid core may be formed from one of: copper, bismuth, tin, gold,
silver, pewter, bronze and mixtures or alloys including one or more
of the foregoing, or from an organic polymer filled with a
metal.
[0014] In various embodiments, the rear core has a Brinell hardness
less than about 50. The rear core may be formed from tin or a tin
base alloy. Alternatively, the rear core may be formed from one of:
copper, zinc, tin and alloys or mixtures including one or more of
the foregoing.
[0015] In various embodiments, the bullet further includes a front
core in tandem alignment with the mid core, with the front core
being positioned adjacent to the nose portion. The front core may
be formed from steel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention will be more fully understood from the
following detailed description taken in conjunction with the
accompanying drawings wherein like elements are numbered alike, and
in which:
[0017] FIG. 1 is a longitudinal, cross-sectional view of a
jacketed, boat-tailed bullet of the prior art;
[0018] FIG. 2 is a longitudinal, cross-sectional view of a
jacketed, boat-tailed bullet in accordance with one embodiment of
the present invention;
[0019] FIG. 3 is a longitudinal, cross-sectional view of components
of the jacketed, boat-tailed bullet of FIG. 2 during
manufacture;
[0020] FIG. 4 is a longitudinal, cross-sectional view of a
jacketed, boat-tailed bullet in accordance with another embodiment
of the present invention; and
[0021] FIG. 5 is a longitudinal, cross-sectional view of a portion
of a jacketed, rebated boat-tailed bullet in accordance with other
embodiments of the present invention.
DETAILED DESCRIPTION
[0022] FIG. 2 is a longitudinal, cross-sectional view of a
lead-free, jacketed, boat-tail bullet (projectile) 50 configured in
accordance with one embodiment of the present invention. In the
embodiment shown, the bullet 50 is formed as a penetrator bullet as
may be used in an M855 cartridge. The bullet 50 has a front core
12, a mid core 52, and a rear core 56 tandemly arranged along a
longitudinal axis 58 of the projectile.
[0023] Enveloping the front, mid, and rear cores 12, 52 and 56 is a
jacket 16, which may be formed from any convenient material such
as, for example, brass (a copper/zinc alloy), copper plated steel,
and the like. In the embodiment shown, the jacket 16 has an ogival
nose portion 18 adjacent to a forward end of the front core 12,
with the nose portion 18 having a closed, flattened tip 60 forming
a small meplat or protected tip. The jacket 16 is crimped around a
rearward end of the rear core 56 to form a base 26 of the bullet
50. As used herein, the forward end refers to the end portion of a
component that is closer to the tip 60 of the projectile during
flight. The rearward end refers to the opposing portion of the
component that is further from the tip 60 of the projectile during
flight.
[0024] Adjacent to the base 26 of the bullet, a sidewall of the
brass jacket 16 is angularly indented for improved ballistic
stability and aerodynamic flight including reduced air drag. This
configuration is referred to as a boat-tail, and is indicated at
22. Disposed between the boat-tail 22 and the nose portion 18 is a
generally cylindrical mid-body sidewall 62. The outside diameter of
the mid-body sidewall 62 (i.e., the caliber) defines the bearing
surface of the bullet 50, which contacts the rifling of a gun
barrel as the bullet 50 is fired through the gun barrel.
[0025] In the bullet 50, the mid core 52 is relatively harder than
the rear core 56. By relatively harder, it is meant that when the
hardness is evaluated by standard testing means, at room
temperature, the mid core 52 is harder than the rear core 56.
[0026] Suitable materials for the front core 12 include steel,
tungsten and tungsten carbide. Preferred materials for the mid core
52 include tungsten base composites. As used herein, the term
"base" means that the composite or alloy contains at least 50%, by
weight, of the material specified (e.g., tungsten). Examples of
tungsten base composites are described in U.S. Pat. No. 5,399,187
to Mravic, et al., which is incorporated by reference herein in its
entirety. Such materials include a sintered composite having one or
more high-density constituent powder materials selected from the
group consisting of tungsten carbide, tungsten, ferro-tungsten and
carballoy, and a second, lower-density constituent consisting
essentially either of a metallic matrix material selected from the
group consisting of tin, zinc, iron, copper, and mixtures or alloys
of one or more of the foregoing, or a plastic matrix material
selected from the group consisting of phenolics, epoxies,
dialyphthalates, acrylics, polystyrenes, polyethylene, or
polyurethanes. In addition, the composite of either type may
contain a filler metal such as iron powder or zinc powder. Other
constituents could also be added in small amounts for special
purposes, and lubricants and/or solvents could also be added to the
metal matrix components to enhance powder flow properties,
compaction properties, ease of die release, etc.
[0027] Other suitable materials for the mid core 52 include copper
and copper alloys, bismuth/tin alloys, gold, silver, pewter (a
tin/antimony/copper alloy), bronze (a copper/tin alloy), and
organic polymers, such as nylon or rubber, filled with a powdered
heavy metal, such as tungsten or copper. Yet other materials for
the core 52 include an annealed copper alloy, such as the copper
alloy designated by the Copper Development Association (CDA) as
copper alloy C10200 (99.95%, by weight, minimum copper).
[0028] Rear core 56 is formed from a malleable material, which
preferably has a Brinell hardness less than about 50 HB when
measured in accordance with American Society for Testing and
Materials (ASTM) standard E10-01, Standard Test Method for Brinell
Hardness of Metallic Materials, using a 500 kg load, 10 mm ball,
and 10-15 second dwell time. The Brinell hardness assigns a number,
HB, related to the applied load and to the surface area of the
permanent impression made by a ball indenter computed from the
equation:
HB=2P/(.pi.D)D-(D.sup.2-d.sup.2).sup.0.5))
[0029] Where:
[0030] P=the applied load in kilogram-force,
[0031] D=the diameter of an indenting ball in millimeters, and
[0032] d=the mean diameter of a formed impression in
millimeters.
[0033] With a Brinell hardness less than about 50 HB, a mechanical
swaging process utilized in standard bullet manufacture is
effective in providing a consistent boat-tail 22 form and adequate
bullet heel closure. Advantageously, the use of the rear core 56
allows the material of the front and mid cores 12 and 52 to be
selected based on ballistic (e.g., weight, density, bullet
penetration) or other requirements, while the rear core 56 will
provide sufficient malleability to ensure that the boat-tail 22 is
properly shaped and that sufficient impinging of the jacket 16 with
the core (i.e. sufficient bullet heel closure) occurs to prevent
propellant gasses from entering the interface between the jacket 16
and the rear core 56. Accordingly, the rear core 56 eliminates the
distortion of the jacket 16 and resulting loss in accuracy and
stability associated with gas penetration.
[0034] A preferred material for the core rear 56 is tin or tin base
alloys, where "base" means that the alloy contains at least 50%, by
weight, of tin. Alternative materials include copper, copper
alloys, bronze, zinc, and mixtures or alloys including one or more
of the foregoing in an annealed or un-annealed state that provides
the malleability to offer adequate boat-tail 22 form and bullet
heel closure. Other alternative materials include non-metallic
materials such as polymers and the like.
[0035] Preferably, the rear core 56 is substantially contained
within the boat-tail 22 of the bullet 50. By "substantially
contained within the boat-tail," it is meant that the forward end
of the rear core 56 preferably extends no more than about one
quarter of the caliber of the bullet (0.25.times.caliber) forward
of a transition point 64 between the boat-tail 22 and the bearing
surface 62 of the bullet. It will be recognized that, because of
the relatively low hardness of the rear core 56 compared to the
front and mid cores 12 and 52, if the rear core 56 is not
substantially contained within the boat-tail 22 (i.e., if the rear
core 56 extends substantially into the area defined within the
bearing surface 62 of the bullet 50), bulging of the rear core 56
may cause bearing surface 62 deformation when the bullet 50 is
fired. In addition, if the rear core 56 is not substantially
contained within the boat-tail 22, the bullet 50 may experience a
greater loss of kinetic energy upon impact with a target due to
excessive deformation or splatter of the relatively soft rear core
56. As described in U.S. Pat. No. 6,085,661 to Halverson, which is
incorporated by reference herein in its entirety, the loss of
kinetic energy due to such excessive deformation or splatter can
diminish the penetrating ability of the front core 12.
[0036] Preferably, the rear core 56 substantially fills the
boat-tail 22 of the bullet 50. By "substantially fills the
boat-tail," it is meant that the rear core 56 fills an area defined
by an inside surface of the jacket 16 between the base 26 of the
bullet 50 and the rearward end of the mid core 52, with the forward
end of the rear core 56 being no less than about one quarter of the
caliber of the bullet 50 (0.25.times.caliber) rearward of the
transition point 64 between the boat-tail 22 and the bearing
surface 62 of the bullet 50. With the rear core 56 substantially
filling the boat-tail 22, the entire boat-tail 22 may be properly
shaped during the bullet forming process.
[0037] In general, the density of each of the front, mid, and rear
cores 12, 52 and 56 is determined in light of the desired
application of the bullet 50. Where the bullet 50 is to be a
lead-free replacement for the 62 grain penetrator bullet 10 used in
an M855 cartridge, shown in FIG. 1, it has been determined that a
tungsten base composite core material with a weight of about 30
grains is preferred for the mid core 52, and a weight of about 4.3
grains is preferred for the rear core 56. The jacket 16 and the
front core 12 of the lead-free replacement bullet 50 are preferably
identical to those found in the existing 62 grain penetrator bullet
10 of the M855 cartridge. In this configuration, the bullet 50 has
substantially the same dimensions and weight as the 62 grain
penetrator bullet used in an M855 cartridge. It is contemplated
that the present embodiment may be applied to bullets of similar
design in various grain weights within a given caliber (e.g., a
5.56 millimeter, 55 grain bullet). It is also contemplated that the
present embodiment applies to other calibers, most notably the 7.62
millimeter 147 grain bullet used in the M80 cartridge, up to and
including 50 caliber.
[0038] A method for the manufacture of the bullet 50 can be
described with reference to FIG. 3. In the method, a jacket
precursor 70 is formed from a malleable metal. The jacket precursor
70 may be formed with an ogival nose 18, cylindrical mid-body
sidewall 72, and a rear sidewall 74. The front core 12 is processed
to a first hardness that is greater than the hardness of the mid
core 52. If the front core 12 is steel, the desired hardness may be
achieved by a thermal process such as carburizing or work
hardening.
[0039] Front and mid cores 12 and 52 are then sequentially inserted
into a cavity 76 defined by the jacket precursor 70, with the front
core 12 being deposited adjacent to the ogival nose 18. While the
rear end of the front core 12 may be bonded to the front end of the
mid core 52, in preferred embodiments, the front and mid cores 12
and 52 are in abutting, but not affixed, relationship.
[0040] After the front and mid cores 12 and 52 are inserted into
the cavity 76, the rear core 56 is deposited into a portion of the
cavity 76 formed by the rear sidewall 74. Preferably, the rear core
56 is manufactured in a spherical shape for ease of feeding during
the bullet assembly process; alternatively, the rear core 56 is
manufactured in slug form from wire, or blanked from strip.
[0041] After the rear core 56 is inserted into the cavity 76, a
swaging die or other mechanical deforming apparatus then deforms
the jacket precursor 70 into an effective jacket 16 as described
above in reference to FIG. 2. A crimp is formed from the rear
sidewall 74 and mechanically secures the front, mid and rear cores
12, 52, and 56 in position. The mechanical deforming step further
deforms both the jacket precursor 70 and the rear core 56 to form a
boat-tail 22.
[0042] Referring to FIG. 4, a longitudinal, cross-sectional view of
a lead-free, jacketed, boat-tail bullet 100 configured in
accordance with another embodiment of the present invention is
shown. The bullet 100 has a mid core 52 and a rear core 56 tandemly
arranged along a longitudinal axis 58 of the projectile. This
embodiment is substantially similar to the embodiment described
with reference to FIG. 2, with the exception that the front core 12
of FIG. 2 has been removed and the mid core 52 now extends from the
nose portion 18 of the bullet 100 to the boat-tail portion 22. The
method for manufacturing the bullet 100 is also substantially
similar to that described above for the bullet 50, with the
exception that the steps related to the front core 12 of bullet 50
are no longer necessary. The bullet 100 of FIG. 4 may be formed as
a penetrator bullet as may be used in an M855 cartridge. The bullet
100 may alternatively be formed as a frangible bullet, as may be
used for shooting ranges.
[0043] In the embodiment of FIG. 4, the mid core 52 is relatively
harder than the rear core 56. In general, the mid and rear cores 52
and 56 may be configured using the same materials, hardnesses, and
densities described above with reference to the embodiment of FIG.
2. However, where the bullet 100 is to be a lead-free replacement
for the 62 grain penetrator bullet used in an M855 cartridge, shown
in FIG. 1, it has been determined that a tungsten base composite
core material with a weight of about 38 grains is preferred for the
mid core 52, and a weight of about 4.3 grains is preferred for the
rear core 56. The jacket 16 of the lead-free replacement bullet 100
is preferably identical to that found in the existing 62 grain
penetrator bullet 10 of the M855 cartridge, as shown in FIG. 1, and
the front core 12 is removed. In this configuration, the bullet 100
has substantially the same dimensions and weight as the 62 grain
penetrator bullet used in an M855 cartridge. It is contemplated
that the present embodiment may be applied to bullets of similar
design in various grain weights within a given caliber (e.g., a
5.56 millimeter, 55 grain bullet). It is also contemplated that the
present embodiment applies to other calibers, most notably the 7.62
millimeter 147 grain bullet used in the M80 cartridge, up to and
including 50 caliber.
[0044] Where the bullet 100 is to be configured as a frangible
bullet, other constituents may be added to the tungsten base
composite of mid core 52 to enhance frangibility. For example, as
described in U.S. Pat. No. 5,399,187 to Mravic, et al., carbon
could be added if iron is used as one of the composite components
to result in a brittle or frangible microstructure after suitable
heat treatment processes.
[0045] In the bullets 50 and 100 described herein, the boat-tail 22
is shown extending from the bearing surface 62 to the base 26.
Alternatively, as shown in FIG. 5, it is contemplated that, in
either bullet 50 or 100, the boat-tail 22 may extend from a rebate
102 in the bearing surface 62 to the base 26 to form what is known
as a rebated boat-tail (RBT). In this embodiment, the transition
point 64 between the bearing surface 62 and the boat tail 22 is the
rebate 102.
[0046] The bullets 50 and 100 described herein employ a rear core
56, which ensures a consistent boat-tail 22 form and adequate
bullet heel closure. The use of the rear core 56 allows the
material of the front core 12 and/or the mid core 52 to be selected
based on ballistic (e.g., weight, density, bullet penetration) or
other requirements, while the rear core 56 will provide sufficient
malleability to ensure that the boat-tail 22 is properly shaped and
provides sufficient impinging of the jacket 16 with the rear core
56 (i.e., bullet heel closure) to prevent propellant gasses from
entering the interface between the jacket 16 and the rear core 56.
Accordingly, the rear core 56 eliminates the distortion of the
jacket 16 and resulting loss in accuracy and stability associated
with gas penetration. Where the rear core 56 is substantially
contained within the boat-tail 22 of the bullet 50 or 100, bearing
surface 62 deformation is avoided when the bullet 50 or 100 is
fired. In addition, where the rear core 56 is substantially
contained within the boat-tail 22, the bullet 50 or 100 will
experience less loss of kinetic energy upon impact with a target,
and thus greater penetration, than if a larger rear core 56 were
used.
[0047] One or more embodiments of the present invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. For example, while the bullets 50 and 100
are described herein as having an ogival nose 18, other nose shapes
may be used as well. For example, nose 18 may be spire (conical)
shaped. Similarly, while the tip 60 of the nose 18 is shaped to
include a small meplat or protected tip, it will be appreciated
that other tip shapes may be used. For example, the tip 60 may be
shaped to form a point; the tip 60 may be shaped as an open tip,
where an aperture is disposed in the jacket 16 at the tip 60; the
tip 60 may be formed as a soft point, where the front core 12 or a
malleable insert protrudes through an aperture in the jacket 16 to
form the tip 60; or the tip 60 may be formed as a hollow point,
where the forward end of the front core 12 or a malleable insert,
exposed either by an open tip or by a soft point configuration,
includes a recess formed therein. Accordingly, other embodiments
are within the scope of the following claims.
* * * * *