U.S. patent application number 10/783032 was filed with the patent office on 2005-08-25 for jacketed ammunition.
Invention is credited to MacDougall, John.
Application Number | 20050183617 10/783032 |
Document ID | / |
Family ID | 34861128 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050183617 |
Kind Code |
A1 |
MacDougall, John |
August 25, 2005 |
Jacketed ammunition
Abstract
A jacketed projectile, preferably with a unique geometry
one-piece steel core to improve penetration of hard targets,
provides good performance regarding chamber pressure, barrel wear
and accuracy by separating the jacket from a central tapered
portion of the core by providing an encircling air gap.
Inventors: |
MacDougall, John; (Montreal,
CA) |
Correspondence
Address: |
David J. French
Stn. "D"
P.O. Box 2486
Ottawa
K1P 5W6
CA
|
Family ID: |
34861128 |
Appl. No.: |
10/783032 |
Filed: |
February 23, 2004 |
Current U.S.
Class: |
102/514 |
Current CPC
Class: |
F42B 12/78 20130101;
F42B 12/06 20130101; F42B 12/74 20130101 |
Class at
Publication: |
102/514 |
International
Class: |
F42B 010/00; F42B
012/00; F42B 030/00 |
Claims
The embodiments of the invention in which an exclusive property or
privelage is claimed are defined as follows:
1. A jacketed projectile comprising a solid central core with a
frusto-conical portion which is not in continuous contact with the
jacket.
2. A projectile as in claim 1 comprising a gap between the jacket
and the core along the surface of said fustro-conical portion of
the core.
3. A projectile as in claim 2 wherein the tapered encircling gap is
air-filled.
4. A projectile in accordance with claim 1 wherein the steel core
comprises carbon steel.
5. A projectile in accordance with claim 4 wherein the hardness of
the steel core is at least 45 on the Rockwell C hardness scale.
6. A projectile according to claim 1 comprising a one-piece core
with a forward portion having an ogival front end, followed by said
frusto-conical portion, whereby the junction of the ogival front
end and the frusto-conical portion provides a relatively smooth
transition zone.
7. A projectile according to claim 1 wherein the conical angle of
the frusto-conical portion of the core is between 0.7 and
1.0.degree..
8. A projectile according to claim 6 further including a short
cylindrical parallel portion of the core extending rearwardly from
the frusto-conical portion.
9. A projectile according to claim 8 wherein the cylindrical
parallel portion of the core is less than 30% of the length of than
the frusto-conical portion.
10. A projectile according to claim 9 further including a
rearwardly tapering end portion of the core after the cylindrical
parallel portion.
11. A projectile according to claim 10 wherein the rearwardly
tapering end portion of the core has a conical angle of about
83.degree..
12. A projectile in accordance with claim 1 wherein the jacket
material comprises gilding metal.
13. A projectile in accordance with claim 12 wherein the gilding
metal jacket comprises approximately 90% copper and 10% zinc.
Description
FIELD OF THE INVENTION
[0001] This invention relates to spin stabilized projectiles fired
from rifled gun barrels, and particularly to small arms
ammunition.
BACKGROUND OF THE INVENTION
[0002] Historically, small calibre projectiles have been made from
lead alloys or contained lead cores. Lead is an easy metal to form
due to its' ease of malleability (very low Young's modulus) and
projectile cores of this material readily deform under the high
engraving stresses associated with a projectile being fired from a
rifled gun barrel. Both of these material properties provide
advantages for projectile design and permit good accuracy
performance and low gun barrel wear.
[0003] However, in order to mitigate the barrel fouling associated
with 1-piece, all-lead projectiles, copper-zinc alloy, (also known
as gilding metal) jackets were introduced. These projectile jackets
are thin enough in profile and ductile enough to deform adequately
under the engraving stresses and transfer the spin from the rifling
and still retain projectile integrity when the projectile leaves
the muzzle of the gun. These 2-piece projectiles are still in
production today, mainly for hunting and some military
applications.
[0004] Further advances to projectile design have resulted in
copper jacket projectiles with a short, conical hardened steel
penetrator in the tip of the projectile and a cylindrical lead core
at the aft of the projectile. Antimony is often added to the core
for increased mechanical strength. The jacket allows the
integration of the two (penetrator and core elements) to reach the
target together and provide as well the desired interior ballistic
performance. This style of three-piece projectile is commonly
referred to as "ball" ammunition. This design has improved terminal
ballistic effects over all-lead core projectiles and allows
increased penetration of hard targets due to the addition of the
very hard penetrator while still permitting good accuracy and
acceptable barrel wear due to the lead/antimony alloy core.
[0005] All NATO 5.56 mm and most common small calibre infantry
weapons in service today currently feature such two-piece core
projectiles due to the relative ease of manufacture, low production
cost, reliability of performance and high lethality upon impact in
the human body. Although the penetration performance of ball
projectiles is superior in metal plates and other hard targets,
performance is sometimes marginal when firing on the NATO standard
steel plate targets during production lot acceptance testing in
cold weather conditions. Thus, the current design is at its design
limits for penetration.
[0006] In recent times, lead has been shown to be a highly toxic
substance and has been banned from use in gasoline and paints, to
name but two commercial products previously containing lead. In
addition, many tons of lead have been entering the water system
every year through the simple loss of lead fishing sinkers and
these too have been prohibited in many localities due to the toxic
effect on the environment and the food chain. As well, the
manufacturing process may expose persons working in the environs of
the projectile production equipment to lead and/or lead dust which
is harmful to the health.
[0007] Now the same health concerns are leading government agencies
around the world to mandate the elimination of lead from the
production of small calibre ammunition. This trend applies to
commercial as well as military products, but numerous technical
challenges have delayed this thrust for military products. One of
the objectives of the elimination of lead is to reduce airborne
contaminants in the shooter's breathing zone.
[0008] The first challenge is to find a suitable replacement
material for lead. Lead is an inexpensive and extremely soft,
easily formed metal, almost ideal for manufacturing purposes.
[0009] Lead is also a high-density material, which is a great
advantage to the ballistician. A heavier projectile for a given
shape will travel farther and retain its velocity better at longer
ranges.
[0010] The objective of any infantry fighter is to incapacitate the
enemy and this is most often achieved by the transfer of kinetic
energy to the target. So, a heavier projectile will transfer more
energy to a given target than a lighter version for impacts with
the same terminal impact velocity.
[0011] Clearly, any lead-free projectile should ideally have the
same muzzle velocity and mass as the steel and lead containing ball
projectile it seeks to replace. The other obvious advantage of
having a lead-free projectile of nearly identical mass relates to
the requirement of retaining the same exterior ballistic
performance. Otherwise all current weapon sighting systems would
require replacement, re-working or extensive re-adjustment and
existing ballistic firing tables would no longer be valid. This
would place an unacceptable logistical burden on most military
forces of any significant size in the world.
[0012] It has not been a simple matter to replace lead as a
material for making projectiles. Alternative projectiles considered
in the past have not been able to maintain the mechanical and
physical properties of lead so as to achieve comparable exterior
ballistic performance. For example, the ability of the projectile
to retain its velocity and energy is measured by its sectional
density and is proportional to the projectile mass divided by the
square of the calibre. Thus, it is seen that a projectile of lower
mass or density will not retain its velocity and energy as well as
a projectile of higher mass and energy. This leads one to conclude
that a projectile comprised of a lower density material should be
longer to retain the same mass as a lead filled projectile.
[0013] Recent efforts to replace lead in projectiles have focused
on high density powdered metals, such as tungsten with polymeric or
metallic binders. However, these replacement materials have yet to
meet all desired specifications and performance goals for
stability, accuracy and economy of manufacture.
[0014] Many different materials and combinations of materials have
been considered as replacements for the lead core in the
manufacture of non-toxic projectiles. See U.S. Pat. No. 6,085,661
in which copper is used as a replacement for lead.
[0015] Another solution being explored is the replacement of lead
with other high density metals such as bismuth. Bismuth metal
possesses material properties similar to those of lead. Shotgun
ammunition that utilizes bismuth shot is also commercially
available, but the density of this metal is still only 86% of that
of lead (9.8 versus 11.4 g/cm3), and again this creates concerns
with regards to exterior ballistic performance. Two other problems
with bismuth are the high cost of the raw material and the relative
scarcity of supply in the world.
[0016] In pelletized projectiles, such as shotgun shot, lead has
been used for many years for hunting waterfowl and other game
birds. Where lead shot has been banned, steel shot has also been
sometimes used. However, due to the high hardness and much lower
density (7.5 versus 11.4 g/cm3), steels are less desirable choices
for use as projectile materials due to the reduced terminal
ballistic effect and increased barrel wear.
[0017] The manufacturers of steel pellet shot shells recommend
using a steel shot at least two sizes larger in diameter than lead
for the same target and similar distances. This further diminishes
effectiveness by decreasing pattern density (the number of pellets
per shot), thus reducing the probability of hit on a moving target.
Although ammunition manufacturers are developing new and improved
additives for use with steel shot, the ammunition appears to cause
excessive wear and undue damage to many shotgun barrels.
[0018] Tungsten and bismuth are two high-density materials that
have been attempted in alloy form with varying degrees of success
in various commercial and military projectile designs (Reference 2
refer to bismuth patents for shot shell pellets or similar here).
High-density depleted uranium and tungsten alloys have both been
used for long rod kinetic energy penetrators for tank ammunition.
Tungsten-nylon and tungsten-tin are two well-known combinations
(Reference 3 refer to U.S. patents here) that rely on advanced
powder metallurgy techniques to achieve the desired form of a
one-piece projectile core for small calibre projectiles.
[0019] The objective of the jacketed tungsten-nylon or tungsten-tin
powder metallurgy one-piece core projectile designs is to create a
new material with an actual density equivalent to the hybrid
density of the steel and lead components they replace, in order to
maintain the volume the two parts occupy. This new single piece
would fit inside a copper projectile jacket, as a "drop-in"
replacement part and has the advantage of not requiring any changes
whatsoever to existing high cadence projectile manufacturing or
cartridge assembly machinery.
[0020] One disadvantage with these powder metallurgy concepts is
that the process does not lend itself well to the manufacture of
components that have to fit inside of another part and retain very
close tolerances. Part of the reason for this problem is due to the
irregular shrinkage associated with the sintering process that is
often required of these powder metallurgy parts to achieve optimal
density.
[0021] Normally, this tolerance problem can only be overcome by
performing post-manufacturing operations on the sintered part, like
grinding. Obviously this increases cost and reduces production
cadence, which is not desirable.
[0022] In addition, tungsten is also costly to obtain and in
relatively scarce supply in the world which makes it considerably
more expensive to manufacture and subject to price volatility.
There are also potential procurement obstacles in the event of
extended armed or economic conflicts involving the nations
possessing this strategic element (or their neighbours) if either
were unfriendly or unsympathetic during any such conflict.
[0023] Clearly, any replacement material for lead should be as
abundant as possible to ensure a secure supply of raw materials and
be as economical as possible to produce since infantry projectiles
are practically considered a commodity nowadays. The replacement
component should preferably be made of a single piece to reduce
manufacturing and projectile assembly costs. Finally, the
manufacturing process of the new core material should not require
any post-manufacturing processes to ensure the current high
production rate and capacity on existing projectile assembly
equipment.
[0024] It is clear from the above that several attempts have been
made in the past to obviate or diminish the use of lead as a
primary material for making projectile cores. Yet, no one
heretofore has achieved satisfactory performance from non-lead
materials.
[0025] This reduces the field of material contenders considerably
and forces one to conclude that in fact a one-piece, all-steel core
could be a serious contender if certain major technical challenges
can be resolved.
[0026] A great advantage of the one-piece steel core projectile is
increased penetration performance in hard targets. Since the mass
of the lead core has been replaced by an equivalent mass of steel,
the penetration of the NATO standard steel plates is easily
accomplished and at even greater ranges. This resolves the marginal
penetration performance problem associated with conventional ball
projectiles.
[0027] Problem 1 of New Projectile
[0028] The main drawback with a hard, one-piece steel core
projectile interior is that suddenly the projectile engraving
forces are dramatically increased and the mechanical stresses
generated will induce premature gun barrel wear through the
enormous friction forces generated.
[0029] The contact surface of the projectile is called the "driving
band". This is the area of the projectile that is in direct contact
with the rifling of the weapon and undergoes plastic deformation
when fired through a gun barrel. In conventional ball projectiles,
the lead core under the copper jacket is in the position of the
driving band. The soft copper jacket and malleable lead core are
ideal materials for a driving band since they are readily
plastically deformed and lengthen longitudinally under axial
compression in accordance with Poisson's ratio for these
metals.
[0030] It must be recalled that the process of firing a
conventional spin stabilized projectile down a gun barrel requires
extruding an oversized cylinder down an undersized tube. The tube
has grooves with a helical twist and causes the cylinder to rotate
inside the barrel, thus ensuring stability during flight. This is
the principle of the spin-stabilized projectile and is sensitive to
the length to diameter ratio of the projectile.
[0031] The stresses on today's modern infantry small calibre
projectiles are enormous due to the very high muzzle velocities and
very fast spin rates involved. The current projectiles are on the
limits of what is possible in mechanical design and production must
be continuously monitored to ensure quality and performance. In
some cases, the metal forming processes involved in manufacturing
the copper projectile jacket induce residual stresses that may
slightly weaken the projectile.
[0032] Problem 1 of Old Projectile
[0033] This is usually a manageable issue with lead-containing
projectiles since the lead is so soft it deforms quite readily and
friction forces are normally manageable. However, the high
engraving stresses on current small calibre infantry projectiles
may occasionally cause "projectile stripping" due to excessive
shear forces acting on the jacket at the annular contact surface at
the rearward end of the short steel penetrator. Projectile
stripping occurs when the local shear stresses exceed the ultimate
strength of the projectile jacket material and the projectile
breaks up upon muzzle exit.
[0034] If projectile stripping occurs, the projectile loses
integrity upon exiting the muzzle, is no longer a controlled
projectile and immediately becomes a critical safety hazard since
its trajectory is unknown. The result of stripping is separation of
the copper projectile jacket, lead core and steel penetrator in
flight which is highly undesirable as it can lead to lethal
accidents for friendly forces training or fighting nearby.
[0035] Projectile stripping has been known to occur when the
diameter of the rearward conical section of the short steel
penetrator exceeds that of the forward cylindrical section of the
lead core. The effect is one of a generating a sharp cutting edge
on the inside of the copper jacket, magnified during the projectile
engraving process.
[0036] Problem 2 of Old Projectile
[0037] One possible solution to the problem of projectile stripping
is to perform a post-production annealing of the projectiles. This
heat treatment acts to relieve some of the residual stresses
induced in the copper jacket during fabrication. This solution
however creates other problems, as there is a negative effect on
the penetration performance since the annealing process reduces the
hardness of the short steel penetrator and reduces penetration
performance in the NATO steel plate targets, especially at lower
temperatures.
[0038] 2 Advantages of New Projectile--Solving Problems 1 & 2
of Old Projectile
[0039] Stripping is not a concern for the one-piece, all-steel core
projectile since there is no longer an internal interface to worry
about, but it does generate other problems, since the hard steel
core does not readily deform and causes greatly increased friction
as the projectile travels down the bore which in turn creates
excessive heating of the gun barrel. Therefore annealing is not
required with the one-piece, all-steel core projectile, so
penetration in hard targets is improved, even at lower
temperatures.
[0040] Problem 1 of New Projectile
[0041] Excessive friction heating due to the one-piece, all-steel
core projectile may lead to accelerated mechanical wear of the
interior surface of the gun barrel (and gun barrel lining if one is
present) that unacceptably shortens the service life of the weapon.
The cause is localized surface melting of the copper projectile
jacket inside the gun barrel which causes a build-up of jacket
material where barrel heating is highest. This phenomenon is known
as "coppering" and must be resolved by reducing friction forces
within the barrel.
[0042] Many modern infantry assault weapons have a metallic lining
inside the gun barrel to extend barrel life. Typically chromium is
chosen for its excellent hardness and resistance to mechanical
wear. Chromium has the additional advantage of providing a smooth
surface for the travel of copper-jacketed projectiles since copper
is not soluble in chromium. Chromium is soluble in steel however,
due to the atomic affinity of copper and iron, so if mechanical
friction increases to such a level that the chromium gun barrel
coating is compromised, coppering will begin to occur rapidly on
the exposed steel surface.
[0043] Problem 2 of New Projectile
[0044] Once coppering starts to occur, the resulting build-up
causes the interior diameters of the rifle lands and grooves to
decrease at the exposed surfaces and now the projectile has to pass
through restricted zones that induce even more localized stress.
This problem will continue to worsen as more projectiles are fired
through the gun barrel unless the barrel is thoroughly cleaned with
a "de-coppering" agent. Coppering often results in a disruption of
proper projectile spin or even complete loss of projectile
integrity, either inside the barrel or upon exiting the muzzle of
the weapon. This additional instability or "projectile yaw" in
flight due to barrel coppering also leads to greatly increased
impact dispersion on the target with a reduction of accuracy and
reduced probability of hitting the target that is unacceptable to
the shooter.
[0045] Problem 3 of Old Projectile
[0046] Another well-known disadvantage with conventional ball
ammunition is its tendency to fragment into many pieces upon impact
with a ballistic gelatine target. Ballistic gelatine is a material
commonly used as a simulation for human tissue to establish
terminal ballistic performance. The requirement for a
non-fragmenting projectile stems from Hague convention IV of 1907,
which forbade projectiles or materials calculated to cause
unnecessary suffering to the opposing soldiers on the battlefield.
An example of a prohibited projectile is the now infamous Dum-Dum
projectile which was judged to cause excessive suffering.
[0047] Projectile fragmentation in the human tissue is the result
of overly rapid transfer of kinetic energy from the projectile to
the target and the resulting excessive bending moment acting on the
already stressed projectile. As the projectile leaves the air and
enters a much higher density medium, such as human tissue, its
stability is immediately compromised and it begins to tumble
rapidly. This is a good means of transferring kinetic energy to the
target, but is considered as causing excessive injury to the
opponent if the tumbling projectile does not remain intact, as is
often the case with the conventional three-piece projectile (ball)
ammunition.
[0048] Since the interior of the conventional ball projectile
comprises one steel and one lead component, the projectile normally
bends at this steel/lead interface and shears the copper alloy
jacket there. This interface acts as a hinge that bends until it
breaks and then allows the lead to disperse in human tissue as tiny
fragments that are very difficult to remove from the soldier after
the battle. Some countries are in the process of considering
restricting or eliminating the use of such fragmenting projectiles
of use by their infantry soldiers, but to date no reliable solution
has been identified
[0049] Advantage of New Projectile--Solution to Problem 3 of Old
Projectile
[0050] A jacketed, one-piece steel core projectile is not sensitive
to high bending moments, since there is no "hinge" upon which the
bending moment may act. As a one-piece steel core projectile
tumbles in tissue, it remains intact and thus does not violate the
Geneva or Hague conventions since it is relatively easy to locate
and remove after the battle. It also does a good job of
transferring energy quickly and incapacitating the opponent in a
more humane manner since the longer projectile will commence
tumbling faster without breaking into numerous small fragments.
[0051] An obvious means of reducing friction forces in an all-steel
core projectile and thereby reducing coppering and stripping is by
simply reducing the projectile diameter.
[0052] However, other potential problems may be encountered with
the performance of spin-stabilized small calibre projectiles
related to a decreased projectile diameter.
[0053] Problem 3 of New Projectile
[0054] If proper projectile spin transfer from the rifling is
disrupted, it is also evidenced by projectile impacts on the paper
target that exhibit evidence of "keyholing" or impact at a
noticeable angle of yaw. This is highly undesirable behaviour for
small arms ammunition since in reality, penetration of hard targets
is thus reduced because the projectile is no longer travelling in a
straight line through the target material.
[0055] Problem 4 of New Projectile
[0056] If the projectile fails to spin properly inside the rifling
of the gun barrel, it may exhibit balloting (uncontrolled yawing
motion inside the barrel) and damage the barrel lands and grooves.
Once this happens, the gun barrel is no longer serviceable and must
be replaced since accuracy is degraded and jacket stripping may
occur.
[0057] Many of these above problems can arise from the choice of
steel or any other hard material as a one-piece replacement for the
existing conventional ball core components.
[0058] Problem 5 of New Projectile
[0059] Properly closing the base of a conventional lead core ball
projectile is not a complex affair, since the lead is easily formed
and readily adheres to the final form imparted onto it by the
copper jacket during the projectile closing operation. This is much
more difficult with an all-steel core, since it cannot be deformed
during the closing operation.
[0060] Problem 6 of New Projectile
[0061] Another design challenge due to the choice of an all-steel
core component is the increased weapon chamber pressure generated
during firing of the cartridge. Maximum chamber pressure values are
strictly regulated in commercial and military ammunition for
obvious safety reasons. If ammunition chamber pressures generated
exceed prescribed limits during firing, catastrophic barrel failure
may result as a worst case, or in the best case, the repeated high
pressure cycles will contribute to accelerated fatigue of the metal
parts and premature wear of the weapon.
[0062] The challenges of achieving maximum muzzle velocity while
maintaining acceptable chamber pressures are well understood in
conventional ball ammunition. The increased pressure experienced
with all-steel core projectiles is directly related to the
increased rifling engraving stresses described above.
[0063] Again, the obvious means of reducing weapon chamber pressure
and projectile engraving stresses is by simply reducing the
exterior diameter of the projectile. This is true of conventional
as well as all-steel core projectiles, but generates a proportional
reduction in accuracy on target, since projectile engraving and
thus uniformity of projectile spin is reduced. If the projectile
diameter is reduced beyond a given point, projectile balloting may
occur. Clearly, simple projectile diameter reduction is not an
acceptable solution to eliminate high chamber pressure, excessive
projectile stress or barrel wear.
[0064] 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 principle of the
invention, and the manner of its implementation. The invention in
its broadest and more specific forms will then be further
described, and defined, in each of the individual claims which
conclude this Specification.
SUMMARY OF THE INVENTION
[0065] Clearly, a one-piece all-steel core needs to be longer than
the conventional steel penetrator and lead core it replaces since
steel is considerably lower in density than lead. It is essential
to achieve the same projectile mass to retain the required level of
muzzle kinetic energy for equivalent terminal ballistic performance
on the target.
[0066] Upon further examination and analysis, it is learned that a
longer, one-piece all-steel core, copper jacketed projectile can be
made to nearly match the weight of the conventional projectile if
it is extended in length to approximately the same length as a
conventional tracer projectile. This means that such a new
projectile design could still be produced and assembled on existing
projectile manufacturing equipment and assembled into complete
cartridges using existing cartridge assembly equipment without
requiring significant or expensive tooling modifications. Thus, the
length over diameter ratio, or L/D must be greater for a steel core
projectile than for a conventional lead core ball projectile in
order to retain the same projectile mass.
[0067] The use of a longer projectile, like the tracer or steel
core projectile requires a greater seating depth of the projectile
into the cartridge case, since the overall cartridge length must be
respected at all times. The cartridge case cannot be crimped onto
the projectile at a lower position either without affecting overall
cartridge length, so this leads to reduced ullage or less empty
space between the projectile base and the surface of the propellant
bed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0068] FIG. 1 shows an image of all lead projectile which has no
jacket like 0.22
[0069] FIG. 2 shows an image of an M193 type projectile.
[0070] FIG. 3 shows an image of an SS109 type projectile.
[0071] FIG. 4 is the same as FIG. 3, but different hatching for
different core materials.
[0072] FIG. 5 shows an image of a longer C78 tracer projectile.
[0073] FIG. 6 shows an image of solid cylinder under axial
compression and how it gets longer.
[0074] FIG. 7 shows an image of the penetrator and core with
stresses acting on the jacket.
[0075] FIG. 8 shows an image of a dum-dum projectile.
[0076] FIG. 9 shows an image of broken projectile therein, (refer
to DREV report).
[0077] FIG. 10 shows an image of the IP core design.
[0078] FIG. 11 shows an image of the IP projectile.
[0079] FIG. 11A is a side section view of a solid core
projectile.
[0080] FIG. 12 is a partial side section view of an all-steel core
projectile with the various portions of the core in evidence.
[0081] FIG. 12A is a side section view of an all-steel core
projectile with the various portions of the core in evidence.
[0082] FIG. 13 is a more detailed sketch showing one embodiment of
the geometry of the steel core in the projectile jacket.
[0083] FIG. 14 is a sketch illustrating the gap present between the
projectile core and jacket.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0084] This invention relates to non-toxic, improved performance,
small calibre all-steel core jacketed projectiles in general,
particularly those up to 12.7 mm calibre.
[0085] Non-toxic projectiles do not contain lead, a soft metal.
Replacing lead presents many manufacturing and performance-related
challenges, like excessive gun barrel wear.
[0086] According to the invention, the design of the all-steel core
must be made in such a way that the accuracy, chamber pressure and
projectile engraving forces are similar to those found in
conventional lead core ball projectiles in order to meet barrel
wear performance requirements. The choice of steel as a core
material is also important in maintaining a cost efficient
projectile while increasing penetration of hard targets.
[0087] One embodiment of the present invention will now be
described, by way of example, with reference to the accompanying
drawings, of which:
[0088] Referring to the drawings, an all-steel core projectile is
made of a copper alloy or gilding metal jacket 11 and an all-steel
core 12.
[0089] A frusto-conical portion of the all-steel core, 14 extends
rearwardly from the ogival front end 15, the frusto-conical portion
having a small angle of approximately 0.85.degree., whereby the
junction of the ogival front end and the frusto-conical portion
provides a relatively smooth blended junction.
[0090] There is a gap between the projectile jacket 11, and the
frusto-conical portion of the core 14, such that the two are not in
continuous contact.
[0091] A short cylindrical section of the core, 16 extends
rearwardly from the frusto-conical portion of the core and serves
as the principle driving band.
[0092] Rearwardly of the short cylindrical section 16, is a short
rearwardly tapering end section, 13 with a conical angle of
approximately 83.degree..
[0093] It is therefore the object of the invention to provide a
jacketed, non-toxic projectile which:
[0094] 1. contains no lead or heavy metals;
[0095] 2. has a one-piece steel core;
[0096] 3. the core is made of a hardened (approx. 0.4% carbon)
steel for improved penetration performance in hard targets;
[0097] 4. meets industrial and military specification requirements
for gun barrel wear;
[0098] 5. chamber pressure;
[0099] 6. accuracy;
[0100] 7. projectile integrity;
[0101] 8. stability in flight; and
[0102] 9. will not fragment upon impact in ballistic gelatine, even
at very short ranges;
[0103] 10. has a thicker copper alloy jacket than standard ball
rounds.
[0104] According to the invention, the forward portion of the
all-steel core has an ogival shaped front end followed by
frusto-conical portion with a small conical angle, whereby the
exterior surface of the frusto-conical portion of the core is not
in continuous contact with the interior surface of the projectile
jacket. The gap between the jacket and the core is filled with air.
The frusto-conical section merges into a short cylindrical section,
followed by a final tapered section that extends backwards from the
rear end of the short cylindrical section.
[0105] The ogival section of the projectile is essential in
facilitating projectile feeding from weapon magazines and/or belts.
An ogive presents a smooth surface with no angles to get caught on
weapon components during feeding to the chamber.
[0106] The projectile core is preferably made of hardened AISI 1038
steel, or other hard material with a Rockwell hardness of 45 or
greater on the "C" scale to ensure improved penetration of hard
targets.
[0107] The jacket of the projectile is preferably made of a ductile
copper/zinc alloy or gilding metal containing approximately 90%
copper and 10% zinc. The thickness of the jacket is also helpful in
meeting the barrel wear criterion. The jacket thickness of the
preferred embodiment is slightly thicker than conventional ball
projectile jackets. A thicker copper alloy jacket requires no
additional special coatings or other special treatment to reduce
friction and acts as a friction reducing medium between the hard
steel core and the gun barrel.
[0108] The projectile is assembled such that the jacket is in
direct contact with the one-piece core on the ogival front end, the
short cylindrical section and the rearwardly tapering end portion.
There is a small air gap between the projectile jacket and the
frusto-conical portion of the core.
[0109] The gap is generated due to the slight angle of the
frusto-conical portion of the core. The angle of this section is
preferably 0.85.degree., but may range between 0.7.degree. and
1.0.degree.. This gap allows the copper jacket material to flow
plastically during engraving and compensate for the unyielding hard
steel core underneath. The deformation of the jacket must be
sufficient to maintain acceptable chamber pressure values, but not
so great as to hinder the transfer of projectile spin and thus
stability. This narrow range of angle is very important to ensuring
the accuracy of the projectile in flight, but is not the only
factor involved.
[0110] The value of the angle of the frusto-conical portion of the
core is critical since too large an angle will result in an
undersized ogival front end and the projectile will not be properly
supported in the barrel. This will lead to an increase in
projectile yaw and reduced accuracy on the target.
[0111] If the angle of the frusto-conical portion of the core is
too small, the gap will be too small, the cylindrical parallel
portion will be too long and increase projectile engraving forces.
The length of the cylindrical parallel portion must be much less
than the length of the frusto-conical portion.
[0112] The ratio of the length of the short cylindrical section
(driving band) of the core to the longer frusto-conical section is
very important for maintaining stability of the projectile in
flight. This ratio should be preferably less than 0.3, but may
range between 0.3 and 0.1, with best results obtained at a ratio of
0.2. If the cylindrical parallel portion is too long, excessive
chamber pressure and barrel wear will result. If this portion is
too short, the projectile will slip in the gun barrel rifling and
diminish in stability in flight, thus affecting accuracy.
[0113] The section of jacketed projectile that acts as the driving
band (over the cylindrical parallel portion of the core) is in
continuous contact with the rifling, while the frusto-conical
section is only partially and progressively in contact with the
rifling. This tapered gap between the jacket and the frusto-conical
portion of the core is key to the invention, since it allows the
projectile to have acceptable internal and external ballistic
performance characteristics, with greatly enhanced terminal
ballistic properties due to the hard steel core. The taper allows
for gradual engraving to ensure acceptable stresses while
maintaining good precision on the target. Other designs were tried,
whereby the gap was cylindrical or other non-conical shapes and the
target accuracy always suffered greatly.
[0114] As the jacketed projectile starts advancing down the barrel
rifling from its starting position in the forcing cone of the
rifling, it gradually and progressively engraves in the lands and
grooves of the rifling. The exact initiation point of engraving
occurs somewhere along the length of the frusto-conical section of
the core and is fully complete when it is in full contact with the
short cylindrical section. This feature is very important since the
various small calibre weapon platforms have different land and
groove diameters, and can be found in various states of wear and in
this way these differences can be accommodated.
[0115] If the gap were to be filled with another material, it would
have to be inexpensive, easy to manufacture, very easily
compressible and not have any deleterious affect on the projectile
jacket during the compressive action of engraving. Otherwise it
could potentially cause the jacket to rupture when it is being
deformed through engraving. This could be a second, less
cost-effective variant however.
[0116] Several tests were made during the development of this new
projectile; involving various combinations of angles and lengths of
the two main core portions. High chamber pressures (380 Mpa) were
measured when the length of the cylindrical section was too long.
This is over NATO specification limits and potentially dangerous.
The final configuration resulted in pressures around 330 Mpa.
[0117] Several tests were also made to establish the optimal angle
of the frusto-conical section. The first test resulted in a barrel
that was worn beyond acceptable limits after only 2,000 rounds
fired in approximately 90 minutes, as per NATO specifications. On
the second try, after several months of design effort the angle was
slightly increased and the length of the cylindrical section was
reduced. This time the barrel only became excessively worn after
4,000 rounds fired.
[0118] On the third and successful attempt, the diameter of the
steel core driving band and the length of the cylindrical section
were slightly reduced and the projectile passed the NATO barrel
wear performance requirements, even after 5,000 rounds were fired.
When the diameter of the driving band portion of the steel core was
further reduced, accuracy on target was greatly diminished.
[0119] These tests were performed over a couple of years.
[0120] Several accuracy tests were also performed over this period
to evaluate the best angle and length of the two key core sections.
The taper angle on the core is essential to meeting accuracy
requirements, since the projectile is progressively supported in
the barrel as it advances down the rifling.
[0121] The radius at the junction of the rear face of the
rearwardly tapering section (the boat tail section) must be
sufficiently large to allow adequate mating of the copper alloy
jacket over the base of the core. If the radius is too small, the
jacket material does not adhere, or close properly. This may result
in high pressure propellant gasses infiltrating between the two
components (core and jacket) and cause projectile stripping the
moment the projectile leaves the barrel and is no longer supported
by the rifling of the gun barrel.
CONCLUSION
[0122] The foregoing has constituted 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 now follow.
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