Patent Application
20110214582
N.A.
N.A.
1. Field of the Invention
Disclosed herein is a high velocity ammunition round that more particularly is sub-caliber with a high density forward portion and a lower density aft portion. Optionally, a sustainer propellant or a base-bleed propellant may be contained within the aft portion.
2. Description of the Related Art
A significant, and uncontrollable, source of error in the accuracy of a long range sniper round is wind. Other sources of error include the effect of gravity during a long time of flight, variations in gun powder charge and drag. Drag causes the bullet velocity to decrease which increases the time of flight to a target. Types of drag that act on a bullet are wave drag (the drag force resulting from aerodynamic shock waves), skin friction drag (the friction between the airstream and the surface of the projectile) and base drag (a vacuum effect at the back of the bullet).
U.S. Pat. No. 6,070,532, titled “High Accuracy Projectile,” discloses a projectile having improved accuracy when fired over long ranges that is formed from a monolithic block of a copper alloy. U.S. Pat. No. 5,297,492, titled “Armor Piercing Fin-Stabilized Discarding Sabot Tracer Projectile,” discloses an armor piercing projectile having a fin stabilized sub-caliber high density rod penetrator and a blind cavity extending inward from an aft end of the projectile. This blind cavity is filled with a tracer composition. Both U.S. Pat. No. 6,070,532 and U.S. Pat. No.5,297,492 are incorporated by reference in their entireties herein.
A sub-caliber bullet with an aerodynamic shape has long-range accuracy due to a high muzzle velocity and reduced time of flight to a target. The bullet has a forward portion, a mid-portion and an aft portion. The forward portion has a density in excess of 10 g/cm3 while the mid-portion has a lower density. In one embodiment, the bullet has an aspect ratio of at least 5:1 and a nose profile that satisfies a Power Law equation:
d=D*(x/L)n (1)
where d is the diameter at a point along the length L, D is a maximum bullet diameter, L is the length, x is a distance rearward from a nose of the bullet and n is a Power Law exponent that is between 0.5 and 0.75. In some embodiments, a blind bore extends into the mid-portion from the aft portion and a sustainer propellant within the blind bore ignites as the bullet exits a gun muzzle to provide a thrust to overcome aerodynamic drag, thereby maintaining the bullet velocity and in certain embodiments accelerating the bullet.
The aerodynamic properties of the sub-caliber bullet are enhanced when the Power Law exponent, n, is approximately 0.67 and the aspect ratio is approximately 10:1. Ballistic stability is enhanced by an aft portion that either has a boat tail, flat base configuration or has a plurality of outwardly and rearwardly extending whiskers symmetrically disposed about its circumference.
In accordance with a second embodiment, the bullet nose profile satisfies the Von Karman Ogive equation:
d=D* ((Θ−(sin(2Θ)/2))/π1/2)1/2 (2)
where
Θ=arccos (1−(2* x)/L). (3)
In certain embodiments, an igniter for the sustainer propellant includes a gas contained within a compressible or malleable container. Compression of the igniter module due to a pressure increase when the gun is fired causes the gas temperature to rise. Release of the hot gas ignites the sustainer propellant at a desired time.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like reference numbers and designations in the various drawings indicated like elements.
As used herein, “small caliber” refers to a bullet or ammunition round capable of being fired from a hand-held weapon such as a rifle or a shotgun. As well as any ammunition referenced in the Army Technical Manual—TM 43-0001-27. Such a bullet or round has a maximum nominal diameter of 1.18 inch or 30 millimeters.
The bullet 10 includes a forward portion 12, a mid-portion 14 and an aft portion 16. Forward portion 12 is formed from a material having a high density, preferably in excess of 16 g/cm3, that resists deformation when exposed to aerodynamic heating. Suitable materials for the forward portion 12 include tungsten, tantalum and their alloys. Anti-armor penetrators act like fluids when they hit a target at hypersonic velocities. The density of the forward portion is therefore more significant than its structure. As a result, high density composite materials, such as tungsten particles embedded in a polymer matrix may be utilized. Certain embodiments may be suitable for a copper-jacketed lead forward portion 10. In these embodiments, the forward portion density may be as low as 10 g/cm3.
The mid-portion 14 is formed from a high strength material having a density less than that of the forward portion 12 to move the center of gravity of the bullet 10 forward of the center of pressure. Preferably, the mid-portion 14 is formed from steel. In some larger bullets, such as 0.50 cal or larger, the mid and aft bodies are made from carbon or glass composite. In some embodiments, as disclosed hereinbelow, the mid-portion 14 is hollow.
An aft portion 16 is formed from a high strength material having a density less than the density of the forward portion 12. Preferred materials for the aft portion are steel and reinforced polymer composites such as a glass or carbon-fiber filled polymer. The aft portion 16 improves aerodynamic stability by contributing to the movement of the center of gravity (CG) forward of the center of pressure (CP). In preferred embodiments, the center of gravity is separated by about 20% of the projectile length from the center of pressure. Aft portion features that contribute to aerodynamic stability may include a boat tail configuration and/or outwardly extending whiskers. At speeds above Mach 1.0, the whiskers create a low drag shock system that contributes to stability.
The bullet 10 has a high aspect ratio to enhance target penetration. Preferably, the aspect ratio, L:D where L is the bullet length and D is the maximum bullet diameter, is at least 5:1 and most preferably is about 10:1.
The bullet profile is preferably established as a ⅔ power law body which has been shown to have superior aerodynamic stability and very low aerodynamic drag at hypersonic speeds. The diameter, d, at any point along the length of the bullet is determined by the equation:
d=D*(x/L)n (1)
where d, D and L have been defined above and x=a distance rearward of the bullet nose 18 along longitudinal axis 20. n is the power law exponent and ranges from 0.5 to 0.75. Preferably, n is ⅔ (0.67). The bullet 10 has symmetry about the longitudinal axis 20 such that at any point d, the latitudinal cross-section of the bullet is circular as shown in
Other aerodynamic shapes with symmetry about longitudinal axis 20 may also be used. For example, rather than the nose coming to a sharp point as with the Power Law equation, a slightly rounded nose may be added to the shape. The Von Karman Ogive equation:
d=D*((Θ−(sin(2Θ)/2))/π1/2)1/2 (2)
where
Θ=arccos (1−(2*x)/L) (3)
is another possible candidate, as is the multi-conic.
For any of the above embodiments, other latitudinal cross-sections may be effective, such as a projectile with a star-shaped cross section having hypersonic aerodynamic stability is known as a “wave rider.”
In
A variation of the sustainer is the base-bleed where the propellant cancels or reduces only the base drag portion of the drag force.
The bullet 10 illustrated in
The bullet 10 illustrated in
The bullet 10 illustrated in
One igniter 34 supports the igniter behind the nozzle 30 at the rear of aft section 16. A primer charge 38, such as a mixture of boron potassium nitrate BKNO3, and Duco Cement (mixture of 1-methoxy-2-propanol acetate, acetone, cellulose nitrate, isopropanol and camphor available from ITW Devcon, Danvers, Mass.) fills the nozzle 30 abutting a compressible sphere 40. When the bullet is fired, the chamber propellant generates a pressure compressing the compressible sphere 40 which ruptures when the argon has a temperature in excess of a desired minimum, such as 1500° F., igniting the primer charge 38 causing an intense flame front to ignite sustainer propellant 31.
The portion of the igniter 34 is illustrated in
Referring to
Suitable materials for the aft cap 44 and fore cap 49 are fully annealed metals such as aluminum or stainless steel or a weldable plastic. When the gun is fired, pressure generated by the cartridge propellant increases pressure exerted on aft cap 44. The compressible sphere 40 is designed to collapse at a pre-determined critical pressure.
Bubble Igniter 34 is small, safe and inert and useful to safely ignite propellant used as a booster or sustainer for gun launched rounds. This bubble igniter may be sized to operate effectively on round sizes from diameters as small as 0.15 inch (3.81 mm) to 0.5 caliber (12.7 mm) in hand held weapons of to guns of any size mounted on a vehicle or tank. The bubble igniter has no electrical connection or activation requirement. It is an inert nugget of argon or other appropriate gas stored at room temperature and modest pressure in one of a number of possible storage vessels. The nugget is nested within the propellant that requires ignition and can stay there indefinitely.
In a hand held weapon firing a small caliber round, the pressure in the gun barrel as it pushes the bullet along is on the order of 50,000 p.s.i. This pressure is communicated to the bullet in the form of acceleration which in turn raises the pressure in the main gun propellant and on the bubble, causing the bubble to collapse pressurizing the argon. As the pressure of the argon is increased, so is the temperature as shown in the PT curve of
The disclosed bullet has an aspect ratio of at least 5:1 and is sub-caliber. To properly align the bullet in the gun and to maximize the pressure build-up behind the bullet, and thereby the velocity of the bullet exiting the gun muzzle, a sabot is employed.
When the aft portion of the bullet includes whiskers, slots 47 are included in the sabot segments 46 to accommodate those whiskers.
The aft retention band 51 is a plastic band that may be formed from any easily breakable material such as nylon or polypropylene.
The sabot diameter (SD) at a front portion 52 of the sabot 48 is full caliber to provide a sliding fit and to align the bullet along the axis of the gun barrel. The front portion 52 is preferably at least twice the caliber in length to support the bullet during travel through the gun bore. Leading edge 54 of the front portion is shaped to enhance air resistance, the leading edge may present a flat surface or inwardly concave surface to maximize the stresses applied by the stagnation pressure of the air in front of the moving sabot/bullet.. Thus, the sabot 48 breaks apart and separates from the bullet upon exiting the gun muzzle.
While a sniper bullet has been described herein, other projectiles requiring accuracy over long distances, such as an anti-aircraft round will benefit.
The Bubble Igniter described above has a number of advantages over conventional igniters. It has reduced complexity and does not require electronics or a timer, thereby reducing cost. A plurality of bubbles in a single igniter smooth the flame /pressure front and increase the reliability of the sustainer burn.
While an electrical ignition system has been developed, it is costly and complex. The Bubble Igniter may achieve the same degree of repeatability but at much lower cost.
The Bubble igniter is also well suited to ignite incendiary devices intended to burn out pillboxes or other deep buried strong holds that require ignition of a solidly packed propellant to provide a high temperature, high energy density source.
Advantages of the bullet desCribed herein may be better understood by the following prophetic Example:
In the Table illustrated in
The round has another reason for increased accuracy and that relates to the aerodynamics of the bullet reacting to side wind forces and crabbing into the wind. When the flight body is flying to the target with the sustainer compensating for drag, the velocity of the round, vaxial, is constant and the drag force is exactly compensated by the force of the sustainer's thrust. If that weren't true, the bullet would either accelerate of decelerate (force=mass×acceleration). It is valid to think about the force of the drag as equivalent to the force of a wind blowing on the nose of the bullet at velocity vaxial. For the bullet, which is axially symmetric, to be stable, the center of mass will be aligned on this vector and be in front of the center of pressure, which will also be along the same vector. The sustainer thrust vector is pointing in the opposite direction and is also collinear.
If a wind blows from the side with velocity vwind, then the total equivalent wind velocity vnew is the vector sum of vaxial plus vwind. This will be at a small angle off the axis of symmetry. Because the flight body is aerodynamically stable, it must swing around so that the nose is always pointing exactly into the wind along the vector vnew, in the manner of a weathervane. Since the sustainer thrust is aligned with the flight body, it must also swing around to be aligned with vnew. This causes a component of the trust vector to be pointing exactly opposite to that of the side wind vwind and because the projectile is neither accelerating nor decelerating, this magnitude must be exactly matched too. At this point, the side force of the wind is exactly cancelled by the canted force of the sustainer. Since the net sideways force is zero, the round will not accelerate to the side. Given that the initial sideways velocity is zero, it will stay zero even as the wind blows.
Thus, when the wind blows on a stable projectile moving at constant velocity due to a sustainer, the projectile axis will crab over slightly to point toward the wind but, amazingly enough, the projectile will continue to fly along its original course as if there were no wind. This is not a new concept, it has been seen on missiles since the Lance missile, but, application to sniper rounds has not been observed. Since wind is the number one problem for snipers, this effect is very important.
One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the use of a copper jacketed lead nose with an aerodynamic shape described herein. Accordingly, other embodiments are within the scope of the following claims.
