Note: Descriptions are shown in the official language in which they were submitted.
CA 02516893 2005-08-22
TITLE: NON-TOXIC JACKETED AMMUNITION
Field of the Invention:
This invention relates to spin stabilized projectiles fired from rifled gun
barrels,
and particularly to small arms ammunition. More specifically, it relates to
ammunition
that is non-toxic in the sense of being free of toxic substances such as
certain heavy
metals.
Background to the Invention
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.
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 as
shown in Figure 1. 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.
Further advances to projectile design have resulted in copper jacket bullets
as in
Figure 2 with an ogival-shaped, a hardened steel penetrator portion in the
front portion of
the projectile and a cylindrical lead core at the aft of the penetrator
portion. Antimony
may be mixed with the lead for increased strength. The jacket allows the
integration of
the two penetrator and core elements to reach the target together and provide
as well the
CA 02516893 2005-08-22
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.
All NATO 5.56mm 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. Some projectiles used as tracers, Figure 3, are of a
greater
length, the added length extending more deeply into the cartridge casing.
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 which
are now
prohibited in many localities due to the toxic effect on the environment and
the food
chain. Additionally, the manufacturing process may expose persons working in
the
environs of the projectile production equipment to lead and/or lead dust
resulting in a
potential health hazard.
These 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.
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. 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.
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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.
Replacing lead as a core material for projectiles has not been a simple
matter.
Previous projectile designs 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 has been observed 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 to the conclusion that, for a given calibre, a projectile
comprised of a
lower density material should be longer to retain the same mass as a lead
filled projectile.
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.
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.
Patent 6,085,661 in which copper is used as a replacement for lead.
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 lead (9.8 versus 11.4 g/cm3),
hence
generating concerns regarding exterior ballistic performance. Two other
problems with
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bismuth are the high cost of the raw material and its relative scarcity of
supply in the
world.
Lead has been used for many years in the form of pelletized projectiles, such
as
shotgun shot for hunting waterfowl and other game birds. Where lead shot has
been
banned, steel shot has sometimes been 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.
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.
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. 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 that rely on advanced powder metallurgy techniques
to
achieve the desired form of a one-piece projectile core for small calibre
projectiles.
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 same 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.
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
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irregular shrinkage associated with the sintering process that is often
required of these
powder metallurgy parts to achieve optimal density.
Normally, this tolerance problem can only be overcome by performing post-
manufacturing operations on the sintered part, such as grinding. Obviously
this increases
cost and reduces production cadence, which is not desirable.
In addition, tungsten is also costly to obtain and in relatively scarce
supply, 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.
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 considered a commodity nowadays. The
replacement
component should preferably, though not necessarily, 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.
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. In
spite of these efforts, no one heretofore has achieved fully satisfactory or
economical
projectile performance from non-lead materials.
This reduces the field of material contenders considerably and forces one to
conclude that in fact a preferably one-piece, all-steel core could be a
serious contender to
providing a solution to the problem listed above if certain major technical
challenges can
be resolved. This is not to exclude the use of other materials for the core
material
including, for example, tungsten, tungsten carbide, tungsten alloys, tungsten-
nylon
compounds, tungsten-tin compounds and mixtures thereof, alternatives. However,
the
following discussion is directed to the use of steel as the preferred core
material.
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A great advantage to adopting a steel core projectile as the solution,
particularly
as a one-piece core, is its increased penetration performance in hard targets.
If the mass
of the lead core were to be replaced by an equivalent mass of steel, the
penetration of the
NATO standard steel plates should be easily accomplished and at even greater
ranges.
This would resolve the marginal penetration performance problem associated
with
conventional ball projectiles. The technical challenges facing old (current
two-piece core
design) and a new (preferably one-piece steel core) ball projectile will be
examined and
the resulting solution is the basis for the new invention.
Technical Challenge 1 of Projectiles (Stripping)
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
tensile
strength of the projectile jacket material and the projectile breaks up upon
exiting the
muzzle.
If projectile stripping occurs, the projectile loses integrity upon exiting
the
muzzle, immediately becoming 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.
Projectile stripping has been known to occur when the diameter of the rearward
end of the ogival section of the short steel penetrator exceeds that of the
forward end of
the 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.
Technical Challenge 2 of Projectiles (Reduced Penetration)
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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.
Technical Challenge 3 of Projectiles (Fragmentation)
Another well-known disadvantage with conventional ball ammunition is its
tendency to fragment into many pieces upon impact with a ballistic gelatin
target.
Ballistic gelatin 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 the 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.
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.
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
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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 by their
infantry
soldiers, but to date no reliable solution has been identified.
Solution to Technical Challenges 1 & 2 of Projectiles With a Jacketed, All-
steel
Core
Annealing is not required with the solution of adopting an all-steel
preferably one-
piece core projectile, so penetration in hard targets is improved, even at
lower
temperatures. Stripping is no longer a concern for the one-piece, all-steel
core projectile
since there is no longer an internal interface between forward and rearward
parts of the
core 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 increased heating of the gun barrel.
Solution to Technical Challenge 3 of Projectiles With a One-piece, Jacketed
All-
steel Core
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 very good job of transferring energy quickly and
incapacitating the
opponent in a more humane manner since the one-piece, longer projectile will
tumble
more rapidly without breaking into numerous small fragments.
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Even a two or more piece steel core will not tend to produce fragments of the
type
associated with lead. Thus use of steel as a core material has, initially, the
appearance of
being the solution of providing an effective lead-free round.
Technical Challenge 1 of a Jacketed All-steel Core Projectile (Increased
Stress)
The main drawback with a hard, steel core projectile interior is that suddenly
the
projectile engraving forces are dramatically increased and the mechanical
stresses
generated can induce premature gun barrel wear through the enormous friction
forces
generated.
The exterior contact surface of the projectile may be 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 directly beneath 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 can slightly lengthen longitudinally
under axial
compression in accordance with Poisson's ratio for these metals.
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 and lands 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 which is sensitive to the length to diameter ratio of
the projectile.
The stresses on today's modern infantry small calibre projectiles are enormous
due to the very high muzzle velocities and very fast spin rates that are
involved. The
current projectiles are at 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 diminish projectile integrity. This
is usually a
manageable issue with lead-containing projectiles since the lead is so soft it
deforms
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quite readily and friction forces are normally manageable. Introducing a one-
piece hard
steel core may strengthen the projectile design, but causes other problems.
Technical Challenge 2 of Jacketed All-steel Core Projectile (Coppering)
S
Excessive friction heating due to the use of an 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 of such an effect 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.
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.
Technical Challenge 3 of a Jacketed All-steel Core Projectile: (Increased
Dispersion)
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
CA 02516893 2005-08-22
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.
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.
However, other potential problems may be encountered with the performance of
spin
stabilized small calibre projectiles related to a decreased projectile
diameter.
Technical Challenge 4 of Poorly Spun, Jacketed, All-steel Core Projectile (Key-
holing)
If proper projectile spin transfer from the rifling is disrupted, it is
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 traveling in a straight line when striking the target material
Technical Challenge 5 of Poorly Spun, Jacketed, All-steel Core Projectile:
(Balloting)
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.
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Many of these above-mentioned 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.
Technical Challenge 6 of a Jacketed, All-steel Core Projectile (Aft End
Closure)
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.
Technical Challenge 7 of a Jacketed, All-steel Core Projectile (Increased
Chamber Pressure)
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 at best, the
repeated high pressure cycles will contribute to accelerated fatigue of the
metal parts and
premature wear of the weapon
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.
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 diameter
reduction does
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generate 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 limit, 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.
It would therefore be desirable to provide a jacketed, non-toxic projectile
and
cartridge which:
1. contains no lead or other toxic substances;
2. has a preferably one-piece core, preferably of steel;
3. has a core suited for improved penetration performance in hard targets;
4. meets industrial and military specification requirements for gun barrel
wear;
5. provides controlled chamber pressure;
6. provides required accuracy;
7. maintains projectile integrity;
8. maintains stability in flight; and
9. will not fragment upon impact in ballistic gelatin, even at very short
ranges.
The present invention endeavours to address such objects.
Provision of a relatively toxic substance free cartridge is a parallel
objective of the
invention. It is riot sufficient to simply eliminate lead from the projectile
if the object is
to provide "non-toxic" round of ammunition. The cartridge must also be free of
toxic
substances.
In small caliber ammunition, a principal source of toxicity is the gaseous
combustion products generated during firing that may be inhaled by the shooter
(in the
form of dust or oxides of toxic elements) arising from the primer.
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Specifically, as detailed in the U.S. Environmental Protection Agency (EPA)
list
of toxic materials and the FBI (Federal Bureau of Investigation) list of toxic
metals, there
is a need to eliminate mercury, lead, barium, antimony, beryllium, cadmium,
arsenic,
chromium, selenium, tin and thallium from primer compositions. In particular,
this
means that long-standing chemically-stable, reliable non-corrosive primer
compositions
containing lead, barium, antimony or other toxic metallic compounds are no
longer
acceptable from an environmental point of view.
There is extensive prior art that addresses avoidance of toxic components in
primers. Going back to 1982, the following US patents are relevant: 4,363,679;
4,522,665; 4,566,921; 4,581,082; 4,608,102; 4,674,409; 4,675,059; 4,689,185;
4,963,201; 5,167,736; 5,353,707; 5,388,519, 5,417,160, 5,466,315 (Erickson)
and
5,547,528 (Erickson). In addition there are European patent N1 699 646 and
French
Patent N1 9602359.
Many of these patents cite diazodinitrophenol (DDNP or drool) as the primary
explosive in combination with one or more oxidizers along with a variety of
other
ingredients necessary for the proper functioning of a primer. The oxidizers
for primers
cited in the prior art listed above include zinc peroxide, manganese dioxide,
strontium
peroxide, strontium nitrate, calcium carbonate, cupric oxide, ferric oxide,
cesium nitrate,
sodium oxalate, zirconium oxide and stannic oxide. In particular, US patent
6,620,267,
the contents of which are adopted herein, addresses a primer composition which
is free of
toxic constituents based on the practice of using potassium nitrate as the
primary
oxidizer. A further object of this invention is to provide a cartridge which
is free of toxic
or poisonous elements generally, and particularly, as referenced above, and
preferably to
employ potassium nitrate as a principal oxidizer in the primary composition.
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
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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
This invention relates to non-toxic, improved performance, small calibre,
jacketed
projectiles and ammunition in general, particularly those up to 12.7mm
calibre. More
particularly, it relates in one aspect to a jacketed projectile comprising a
central core with
a midsection or central portion which is not in continuous circumferentially
contact with
the jacket for at least a portion of its length. The jacket in this region is
"unsupported" by
the core in the sense that little resistance to engraving forces applied to
the jacket in this
region is provided by material underlying the jacket. This absence of support
arises
within a portion of the midsection of the core. As engraving develops along
the jacket of
the projectile during firing support for the jacket overlying the midsection
can
progressively build-up. Progressive engraving occurs in the sense that the
forces required
to develop engraving along the jacket increase as the gap between the jacket
and the mid-
section narrows. In this manner, the discontinuous development of stresses
minimized.
According to a further aspect of this invention, this projectile is combined
in a
cartridge which is free of toxic substances and particularly free of specific
toxic metals.
This produces a round which will be considered "environmentally friendly" in
terms of
eliminating the release of toxic substances into the environment.
According to a preferred variant of the projectile aspect of the invention
this
midsection is tapered or generally frusto-conical in shape. Further, in a
preferred
embodiment, a separation or gap is provided between the jacket and the core
along the
surface of the midsection or fustro-conical portion of the core. This gap
preferably
encircles the frusto-conical central portion and is itself tapered. The frusto-
conical portion
of the projectile core preferably has a half conical angle, referring to the
included angle
of the cone as the conical angle, of between 0.7° and 1.3 °,
more preferably between .07°
CA 02516893 2005-08-22
and 1.0° and even more preferably about 0.85° to 0.95°
for a 5.56 mm round, ideally
0.85°.
According to the most preferred embodiment of the projectile aspect of the
invention, the tapered encircling gap is air-filled. However, such gap may be
filled with
any compressible substance which is compatible with incorporation into a small
arms
projectile and which contributes little support to the jacket during the
engraving of the
jacket by rifling in a barrel, e.g., it provides only a small portion of
resistance to
engraving forces over at least a portion of the midsection of the projectile.
Although not essential, a projectile according to the invention preferably has
a
steel core, which comprises carbon steel, the steel core preferrably being in
one piece.
This steel core material may have a hardness of at least 45 on the Rockwell C
hardness
scale. An alternate example of the core material could be tungsten or any
tungsten alloy.
The jacket material preferably comprises gilding metal which is suited to be
engraved
upon firing through a rifled barrel. The gilding metal jacket may comprise,
for example,
approximately 90% copper and 10% zinc.
The core of the projectile is preferably of one-piece with a forward portion
having
an ogival front end, optionally truncated at its forward tip, followed by the
tapered or
frusto-conical mid-section portion, tapering towards its projected apex in the
forward
direction. The junction between the rear of the ogival front-end portion and
the front end
of the midsection/frusto-conical portion preferably provides a relatively
smooth transition
zone between the two sections, e.g. without a ridge or ledge.
Rearwardly of the midsection portion, the projectile core is provided with a
shorter cylindrical portion preferably with a constant circular diameter. In
this region, the
jacket is in substantial contact with the core. This contact need not be
absolutely
complete. For example, the cylindrical surface of the core may be fluted or
otherwise
shaped to provide small gaps, so long as the driving band function is not
impaired. This
cylindrical region extends rearwardly towards a final, rearward, inwardly
tapering, end
portion of the core - a "boat-tail". Preferably, the cylindrical portion of
the core is less
than one third, more preferably less than 30% of the length of the midsection
portion.
16
CA 02516893 2005-08-22
Preferably the rearward inwardly tapering, conical, boat-tail end portion of
the core has
an half conical angle of about 7°. The projectile jacket overlies such
inwardly tapering
end portion and preferably extends over onto the final end-surface of the core
to ensure
effective attachment of the j acket to the core.
In order to achieve the same projectile mass (to retain the required level of
muzzle
kinetic energy for equivalent terminal ballistic performance on the target), a
one-piece
all-steel core made in accordance with the preferred embodiment of invention
is longer
than the corresponding ball round with a conventional steel penetrator and
lead core.
This extra length is contained within and absorbed by the cartridge casing.
The length of
the projectile of the invention to achieve the objective may be approximately
the same
length as that of a conventional tracer round cf Figure 3, of corresponding
calibre. Thus,
the projectile of the invention is fitted into a cartridge casing so as to
provide a cartridge
having the same overall length as a corresponding standard round, enabling the
projectile
of the invention to function in unmodified existing weapons. Stated
alternately, a
cartridge according to the invention including including its casing is
preferably
dimensioned to fit into a standard firearm wherein the overall length of the
projectile may
be greater than that of a conventional ball projectile of similar caliber but
wherein the
projectile, when fitted into its casing, provides a cartridge with a length
suited to fit into a
standard firearm having a casing of the same diameter.
The projectile as described is combined in a cartridge wherein the projectile,
the
casing and both the propellant and the primer are free of toxic substances as
referenced
above. In particular, such ammunition, including the propellant and primer, is
free of the
following specific toxic metals: mercury, lead, barium, antimony, beryllium,
cadmium,
arsenic, chromium, selenium, tin and thallium from primer compositions. As a
preferred
formulation, the primer has a composition as in Table 1 hereto which is
similarly free of
such toxic substances.
17
CA 02516893 2005-08-22
The foregoing summarizes the principal features of the invention and some of
its
optional aspects. The invention may be further understood by the description
of the
preferred embodiments, in conjunction with the drawings, which now follow.
Brief Description of the Drawings
Figure 1 shows cross-sectional view of a prior art M193 type projectile with a
one-piece jacketed lead core.
Figure 2 shows a cross-sectional view of a prior art SS 109 or C77 type
projectile
incorporating a front steel penetrator portion.
Figure 3 shows a side view of a longer prior art, C78, tracer projectile.
Figure 4 shows a side view of the core for a projectile according to the
invention.
Figure 5 shows a cross-sectional side view of a complete projectile according
to
the invention.
Figure 6 is a side view as in Figure 4 indicating preferred angular dimensions
and
relative proportions for the central core portion and rearward end portions of
the
projectile, according to the invention.
Figure 7 is a cross-sectional side view of a toxin-free cartridge
incorporating the
projectile of the invention.
Description of the Preferred Embodiment
Figures l, 2 and 3 represent prior art configurations as referenced above.
According to a preferred embodiment of the invention as shown in Figures 4, 5
and 6, a projectile is provided with an all-steel core 12 that is contained
within a jacket 11
of copper alloy or gilding metal. An ogival front-end section 10 of the
projectile
facilitates projectile feeding from weapon magazines and/or belts by
presenting a smooth
surface with no angles to get caught on weapon components during feeding to
the
18
CA 02516893 2005-08-22
chamber. The core 12 has a corresponding ogival shape, however the core may be
truncated at its forward leaving an optional, small, air gap at the forward
tip of the
projectile as an artifact of manufacture.
Extending rearwardly from the ogival front end 10 is a midsection that
incorporates a frusto-conical portion 14 of the all-steel core 12, the frusto-
conical core
portion 14 having a small half conical angle, e.g. an angle of approximately
0.85°. This
small angle of taper facilitates ensuring that the junction 17 of the ogival
front end of the
core 12 and the frusto-conical core portion 14 is a relatively smooth,
blended, junction
17. Although the surfaces need not be perfectly co-aligned at their juncture,
they are
preferably free of any substantial ridge on step at their point of juncture.
The presence of the small conical taper in the frusto-conical portion 14
enables
the partially cylindrical jacket 11 to be formed so that the exterior surface
of the frusto-
conical core portion 14 is not in continuous contact with the interior surface
of the
projectile jacket 11. This has the effect of removing a portion of the support
that would
otherwise be provided to the jacket 11 if it were directly adjacent to the
core 12. Thus in
the depicted preferred embodiment there is a gap 15 separating the projectile
jacket 11
and the frusto-conical core portion 14 so that the two are not in continuous
contact over
the midsection portion of the projectile. In the preferred embodiment the gap
15 between
the jacket 11 and the core 12 is filled with air.
The point of commencement of the separation is shown in Figure S as coinciding
with the juncture between the jacket 11 in the ogival front portion 10 and
midsection of
the core 12. This is slightly forward of the juncture between the ogival front
portion of
the jacket 11 and the commencement of the cylindrical portion of the jacket 11
whereby
the gap 15 is formed.
A short cylindrical section 16 of the core 12 extends rearwardly from the
frusto-
conical portion 14. The jacket 11 is in contact with the core 12 in this
region so that this
section serves as the principle driving band area. Over the cylindrical
section 16, the
jacket 11 will become fully engraved on firing. Rearwardly of the short
cylindrical
19
CA 02516893 2005-08-22
section 16 is a shorter rearwardly-tapering end section 13 with a half conical
angle of
approximately 7°.
The projectile core 12 in its steel format 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 assistant in improved penetration of hard targets. The jacket 11 of
the projectile
is preferably made of a ductile copper/zinc alloy or gilding metal containing
approximately 90% copper and 10% zinc. The jacket 11 thickness in the driving
band
area of the preferred embodiment, and optionally everywhere is slightly
thicker than that
of conventional ball projectile jackets, e.g. 0.635mm for a new 5.56 mm round
as
opposed to 0.559mm for a standard 5.56 mm ball round. The jacket 11 wall need
not be
of constant thickness. 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 12 and the gun barrel.
The projectile is assembled with the jacket 11 in direct contact with the
preferably
one-piece core 12 along the ogival front end 10, the short cylindrical section
16 and the
rearwardly tapering end portion 13. However, by reason of the frusto-conical
shape of
the intervening middle portion 14 and the fact that the jacket 11 is generally
cylindrical in
shape, particularly on its inside surface, there is a small separation or gap
15 between the
projectile jacket 11 and the frusto-conical portion 14 of the core 12. The
conical angle of
the frusto-conical portion 14 is, for a 5.56 mm round, preferably the greater
portion of
0.85° to 0.95°, but may preferably range between 0.7° and
1.0°. This gap 15 allows the
copper jacket material over the mid-section to flow plastically during
engraving and
without rupturing from no significant interference from the unyielding hard,
steel core 12
underneath, at least in the forward portion of the midsection. The deformation
of the
jacket 11 must be sufficient to maintain acceptable chamber pressure values,
but not so
great as to hinder the transfer of spin to the projectile required for
stability. The range of
permitted angles for the tapered portion 14 of the core 12 is also important
for ensuring
the accuracy of the projectile in flight, but this is not the only factor
involved.
CA 02516893 2005-08-22
The value of the angle of the frusto-conical portion is additionally important
since
too large an angle could result in an insufficiently supported ogival front
end portion 10
whereby the projectile may not properly seat in the barrel. This can lead to
an increase in
projectile yaw in flight and reduced accuracy on the target. If the angle of
the frusto-
conical portion 14 is too small, the gap 15 will be too small and increase
projectile
engraving forces will arise.
Further, it is highly preferable that the length of the cylindrical parallel
portion 16
be less than the length of the frusto-conical portion 14, preferably
substantially less. The
reason for this is as follows.
The ratio of the length of the short cylindrical section 16 of the core 12 to
the
longer frusto-conical section 14 is important for maintaining stability of the
projectile in
flight. This ratio should be preferably less than one third, more preferably
less than 0.3,
ranging between 0.3 and 0. l, with best results obtained at a ratio of about
0.2 in 5.56mm
projectiles. If the cylindrical parallel portion 16 is too long, excessive
chamber pressure
and barrel wear will result. If this portion 16 is too short, the projectile
will slip in the
gun barrel rifling and diminish in stability in flight, thus affecting
accuracy.
The section of jacketed projectile that acts as the main driving band area
(over the
cylindrical portion 16 of the core) is in continuous contact with the rifling,
while the
frusto-conical section 14 of the core 12 is only partially and progressively
supplying
support to the jacket 11 while it is in contact with the rifling. Engraving
forces are
highest over the cylindrical portion 16.
The tapered gap 15 between the jacket 11 and the frusto-conical portion 14 is
a
useful aspect of 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 the gradual build-
up of
engraving stresses to ensure only acceptable stresses arise while maintaining
good
precision on the target.
Other designs were tried wherein the gap 15 was cylindrical or of other non-
conical shapes with the result that less a satisfactory, though functional,
target accuracy
21
CA 02516893 2005-08-22
was achieved. The preferred use of a tapered or conical midsection does not
exclude
other shapes from the scope of the invention, so long as adequate performance
is
provided, but the preferred embodiment incorporates a frusto-conical shape.
As the jacketed projectile starts advancing down the barrel rifling from its
starting
position in the forcing cone of the rifling, it gradually 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 14 and engraving occurs more readily where the
gap 15 is
largest. Engraving is fully complete when the barrel proper is in full contact
with the
short cylindrical section 16. This feature is important since the various
small calibre
weapon platforms have different land and groove diameters, and can be found in
various
states of wear. Using the projectile of the invention, these differences can
be
accommodated.
The gap 15 may be empty or occupied by a substance or material. The material
chosen to occupy the gap 15 is preferably inexpensive, easy to manufacture,
easily
compressible and therefore free of any tendency to provide a deleterious
effect on the
projectile jacket 11 during the compressive action of engraving. Otherwise
such material
could potentially cause the jacket 11 to rupture when it is being deformed
through
engraving. Air has been found to be the most satisfactory substance. Other
gases may be
employed or a compressible or engraveable solid could also be employed.
Accordingly, when reference is made herein to an "air gap" or "gap", this is
intended to refer to the region between the core 12 and the jacket 11 in the
most general
sense. Whatever material occupies the space, it is acceptable so long as it
provides
initially little or no support to the jacket and allows the projectile to
respond appropriately
when the projectile is engaged with rifling during firing.
. The projectile of the invention is preferably fitted into a cartridge casing
so as to
provide a cartridge having the same overall length as a corresponding standard
round.
Based on the use of steel as the core material, the length of the projectile
of the invention
can preferably approximate the same length as that of a conventional tracer
round of
Figure 3, of corresponding caliber. This enables the projectile of the
invention to
22
CA 02516893 2005-08-22
function in unmodified existing weapons. While the lengthened projectile
encroaches on
the seating depth of the projectile into the cartridge case, nevertheless, as
with tracer
rounds, sufficient space remains to provide a full propellant charge effective
to achieve
desired performance. Care must be taken, however, when selecting an
appropriate
propellant to avoid excessive compression of the propellant inside the
cartridge case.
The radius at the junction of the rear face of the rearwardly tapering section
13
(the boat tail section) must be sufficiently large to allow adequate mating of
the copper
alloy jacket 11 over the base of the core 12. 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 12 and jacket 11) and cause
projectile
stripping the moment the projectile leaves the barrel and is no longer
supported by the
rifling of the gun barrel.
Several tests were made during the development of this new projectile;
involving
various combinations of angles and lengths of the two main core portions 14,
16. High
chamber pressures (380 Mpa) were measured when the length of the cylindrical
section
16 was too long. This is over NATO specification limits and potentially
dangerous. The
final configuration resulted in pressures around 330 Mpa.
Several tests were also made to establish the optimal angle of the frusto-
conical
section 14. 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 test
specifications.
On the second try, after several months of design effort the angle was
slightly increased
and the length of the cylindrical section 16 was reduced. This time the barrel
only
became excessively worn after 4,000 rounds fired.
On the third and successful attempt, the diameter of the steel core 12 in the
driving band region, made-up by increasing jacket 11 thickness, and the length
of the
cylindrical section 16 were slightly reduced. With this change the projectile
passed the
NATO barrel wear performance requirements, even after 5,000 rounds were fired.
When
the diameter of the driving band portion 16 of the steel core 12 was further
reduced,
accuracy on target was substantially diminished.
23
CA 02516893 2005-08-22
These tests are in respect of meeting NATO standards. They do not represent
minimum functionality, which may be well below such standards for other
military or
commercial applications.
Figure 7 depicts a cartridge 20 incorporating the projectile of the invention
in
combination with other substantially non-toxic components. A casing 21 made of
brass
or other suitable material has a head-end 22 incorporating a primer cap 23.
Within the
primer cap 23 is a primer composition that is substantially free of toxic
substances. The
casing 21 further contains a propellant that is substantially free of toxic
substances. As an
example to demonstrate that the core need not be in one piece, although this
is highly
desirable, the core in this Figure 7 is shown as being assembled from two
inter-fitting
portions.
A preferred primer composition for inclusion in the primer cap 23 is made
according to the formulation of Table 1. This formulation is just an example,
but a
preferred example of a non-toxic primer composition.
The primer composition in the case of use of a hygroscopic oxidizer is
combined
with waterproofing vapour barrier material to protect the oxidizer from undue
absorption
of atmospheric water vapour. A preferred oxidizer is potassium nitrate (KN03),
which is
coated with nitrocellulose, as a preferred coating material to protect the
KN03 from its
hygroscopic nature. Sufficient nitrocellulose coating is provided to ensure
that the
performance of KN03 as an oxidizer is not degraded by the presence of water
that would
otherwise be absorbed by the KN03 from the environment. Other oxidizers
susceptible
to moisture absorption, e.g. strontium nitrate Sr(N03)2 can be similarly
protected.
In a non-toxic primer DDNP may be employed as the primary explosive and
optionally, PETN may be present as a secondary explosive. Tetrazene may be
added to
increase sensitivity to friction. Also optionally ZnO.Zn02 (containing at
least 50-60% of
Zn02) may be present as a secondary oxidizer, with KN03 predominating as the
principal
source of oxygen.
24
CA 02516893 2005-08-22
As further preferred constituents of the primer composition, silicon carbide
(carborundum) or other equivalent material may be present to increase
sensitivity to
friction (i.e. as a "frictionator") and aluminum powder may be used as the
fuel.
Finally, a binder was added to facilitate the compaction of the priming mix
into
primer cups and to prevent powder loss during subsequent handling.
Various ratios of the ingredients, as indicated in the column of Table 1
giving
weight ranges, can be used depending on the desired characteristics of the
final product.
An optimum composition, as detailed in the preferred weight column of Table 1,
was
determined based on sensitivity to impact and friction tests, sensitivity to
drop tests, the
quantity of gas generated after ignition in a closed bomb, ease of control of
charge weight
in primer cups, and ballistic performance when fired in reduced energy
cartridges as
represented by US Patent 5,359,937.
As already stated above, the preferred primer composition is shown in Table 1.
The DDNP used had a molecular weight of 210 g, a density of 1.63 g/cc, and an
ignition
temperature of 200°C. It's particle size distribution was approximately
80% > 50 m and
20% < SO m. The PETN used met MIL-P-387 specifications and had a particle size
of
about 100 m. The tetrazrene was manufactured according to MIL-T-46938.
KN03 powder (Class 2, MIL-P-156) was added to a previously-prepared 3%
solution of Nitrocellulose (NC) in acetone and the resulting slurry was mixed
in an
appropriate blender before being dried at 60°C for 24 h and then ground
to a particle size
of about 100 m. This grinding process may expose portions of the KN03 to the
atmosphere, but a sufficient amount of KN03 remains either fully or partially
coated to
provide the necessary resistance to moisture absorption. "Coating" as used
herein reflects
this degree of coverage of the oxidizer as described.
The ZnO.Zn02 (at least 50 to 60% Zn02) had a particle size < 45 m, the
aluminum powder (< 45 m) was according to MIL-A-512A and the SiC was of a
commercial grade (approx 100 m). The binder was an acrylic resin.
To prepare the mix, the explosive ingredients were mixed together with the
DDNP initially containing 30 to 40% water, the PETN containing 15% water, and
the
CA 02516893 2005-08-22
tetrazene 20 to 30% water. Next, the non-explosive ingredients, including KN03
previously coated with NC, were mixed dry separately. The dry non-explosive
mixture
was then added to the wet mixture of explosive ingredients and thoroughly
mixed. The
water content was maintained at 15%, by adding additional water if necessary.
Finally,
the binder was added and a final mixing performed. The finished mix was stored
at 4°C
prior to use.
During loading, the mix was pressed through a standard perforated primer plate
to
form pellets of the desired size for loading into primer cups. Since DDNP is
much lighter
than the lead styphnate usually used as the primary explosive in conventional
primers, the
nominal weight of the charge was reduced by about 30%. The resultant charge
weight
was 12.6 g/milligrams.
After charging the cups, a lacquered paper foil was tamped onto the wet
charge,
and the charge was compacted. A layer of sealing lacquer was placed on top of
the foil
before drying the primers at 50°C. Following drying, the primers were
inserted into
cartridge cases in preparation for ballistic evaluation. In all respects, the
method of
preparing the primers followed general well-known procedures in the field. The
propellant 25 was based upon standard, well-established formulations
containing, for
example, nitrocellulose, nitroglycerin, dibutylphtalate, diphenylamine,
calcium carbonate,
potassium nitrate, tin dioxyde and graphite.
On this basis, a cartridge can be produced that is free of the most serious
toxic
metals, both in respect of the chemicals employed and in respect of the
projectile.
Conclusion
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.
26
CA 02516893 2005-08-22
These claims, and the language used therein, are to be understood in terms of
the
variants of the invention which have been described. They are not to be
restricted to such
variants, but are to be read as covering the full scope of the invention as is
implicit
within the invention and the disclosure that has been provided herein.
27
