High velocity ammunition round

Abstract

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/cm3 while the mid-portion has a lower density. The bullet has an aspect ratio of at least 5:1 and a diameter, d, that satisfies a Power Law equation: d=D*(x/L)n

Description

CROSS REFERENCE TO RELATED APPLICATION(S)

N.A.

U.S. GOVERNMENT RIGHTS

N.A.

BACKGROUND

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.

BRIEF SUMMARY

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))/π^1/2)^1/2  (2)whereΘ=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.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a planar view of a sub-caliber bullet as described herein.

FIG. 2 is a latitudinal cross-sectional view of the sub-caliber bullet illustrated in FIG. 1.

FIG. 3 is a longitudinal cross-sectional view of a first embodiment of the sub-caliber bullet illustrated in FIG. 1.

FIG. 4 is a longitudinal cross-sectional view of a second embodiment of the sub-caliber bullet illustrated in FIG. 1.

FIG. 5 is a longitudinal cross-sectional view of a third embodiment of the sub-caliber bullet illustrated in FIG. 1.

FIG. 6 is a longitudinal cross-sectional view of a fourth embodiment of the sub-caliber bullet illustrated in FIG. 1.

FIG. 7 illustrates an igniter for use with the second and fourth embodiment illustrated in FIGS. 4 and 6.

FIG. 8 graphically relates Collapse Pressure to Sphere Wall Thickness for the igniter of FIG. 7.

FIG. 9 graphically relates Collapse Pressure to Propellant Combustion Temperature for the igniter of FIG. 7.

FIG. 10 is an exploded isometric view of sabot components for use with the sub-caliber bullets disclosed herein.

FIG. 11 is an isometric view of a sabot assembled from the components of FIG. 10.

FIG. 12 is a cross-section view of the sub-caliber bullet disclosed herein having an attached sabot and loaded into a cartridge.

FIG. 13 is an enlarged view of the aft portion of the sub-caliber bullet as loaded into the cartridge of FIG. 12.

FIG. 14 is an isometric view of the sub-caliber bullet having an attached sabot and loaded into a cartridge that is illustrated in FIG. 12.

FIG. 15 presents various calculated bullet parameters to compare an aerodynamic bullet as described herein with conventional bullets.

FIG. 16 is an enlarged view of a compressible bubble used with the igniter illustrated in FIG. 7.

FIG. 17 is cross-sectional view of a fifth embodiment of the sub-caliber bullet illustrated in FIG. 1.

Like reference numbers and designations in the various drawings indicated like elements.

DETAILED DESCRIPTION

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.

FIG. 1 is a planar view of a sub-caliber bullet 10 that has long-range accuracy and is effective as a sniper round. As compared to a conventional bullet, the bullet 10 has a reduced mass to exit a muzzle at a higher initial velocity. The bullet 10 has an improved aerodynamic shape to reduce air resistance and thereby reaches a target quicker than the conventional bullet. Two advantages of a reduced time of flight are there is less time for a cross-wind to deflect the bullet and less time for the bullet trajectory to be influenced by gravity. The reduced flight time also attenuates error due to gunpowder charge variations. As the bullet takes less time to reach the target, there is less time for gravity to influence trajectory due to gunpowder variation caused velocity change.

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 FIG. 2.

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))/π^1/2)^1/2  (2)whereΘ=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.”

FIGS. 3-6 illustrate various embodiments of the sub-caliber bullet 10 in cross-sectional representation. In FIG. 3, the bullet 10 has the front portion joined to the mid-portion 14 by a projecting portion 22 that may be a threaded post or brazed rod. The aft portion 16 is formed as a portion of the mid-portion 14 and includes a boat tail 24.

In FIG. 4, the mid-portion 14 of the bullet 10 includes a blind bore 26 that is open at the aft portion 16. The blind bore 26 has a substantially constant cross-sectional area through the mid-portion 14 that terminates at a restricted throat 28 adjacent the aft portion 16. The blind bore has diverging sidewalls through the aft portion forming a nozzle 30. The blind bore 26 is filled with a sustainer propellant that preferably ignites as the bullet leaves the muzzle of a gun, or very shortly before that moment, providing a drag canceling thrust to maintain or boost velocity.

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 FIG. 5 includes whiskers 32 projecting outwardly and aftward from the aft portion 16. The whiskers, which are metal wires having a length of about one caliber and a gage of between 0.01 and 0.02 inch diameter are typically formed from heat resistant steel and provide aerodynamic stabilization without a need to spin the projectile. The whiskers move the center of pressure aftward increasing the separation between center of gravity and center of pressure improving aerodynamic stability in flight. A plurality of whiskers are symmetrically disposed around the circumference of the aft portion 16. For example, four whiskers may be disposed at 90° intervals about the circumference. Rather than whiskers, fins may be used for aerodynamic stability. Typical fins have a standard airframe shape or are ladder-shaped.

The bullet 10 illustrated in FIG. 17 has a relatively soft, deformable, tip 64 formed from a material such as copper or aluminum. The tip deforms on impact to expand the area over which the bullet's momentum is dispersed. Increasing the area enhances the stopping power of the bullet and also minimizes penetration of the bullet impact, a consideration for certain ATF and FBI protocols where penetration of a bulletproof vest is prohibited. A high density rear section 66 of the forward portion 12 has sufficient volume that the cumulative density of the forward portion remains above 10 g/cm³ and preferably above 16 g/cm³ as described herein.

The bullet 10 illustrated in FIG. 6 combines whiskers 32 with a blind bore 26, throat 28, nozzle 30 assembly to receive a sustainer propellant. Any suitable propellant may be used as the sustainer propellant, such as HTPE (hydroxyl-terminated polyether) or HTPB (hydroxy-terminated polybutadiene). Any suitable igniter may be utilized to ignite the sustainer propellant. To avoid damage to the gun, the sustainer propellant is preferably ignited when the bullet exits the muzzle or very shortly before that moment. To maximize bullet speed to the target, the sustainer should provide sufficient thrust to at least equal aerodynamic drag for up to two kilometers of flight and nominally for about one kilometer of flight. The sustainer generates thrust to counteract wave drag and skin friction drag. The gases expelled by burning of the sustainer fill the void created by the vacuum at the base of the projectile overcoming base drag.

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 FIG. 7. The retention plate 36 includes one or more apertures 41 with a plastic seat 42 lining at least one aperture to seat compressible sphere 40. A number of apertures 41, nominally from 1 to 6, contain a compressible sphere 40. When the gun is fired, the main propellant in the gun cartridge is ignited generating a pressure wave that presses on aft cap 44 compressing the compressible sphere 40 increasing the pressure of a gas 45 contained within the compressible sphere causing a gas temperature increase. The gas 45 should also be inert and non-hazardous. A preferred gas is argon. Once the collapse pressure is reached, the argon bursts through the fore cap 49 at a temperature of well above 1500° F. and ignites the sustainer propellant.

Referring to FIG. 16, the compressible sphere 40 need not be spherical, merely spheroidal is acceptable. An exemplary compressible sphere is hermetic, on the order of 0.2 inch in diameter, and filled with a gas that has a significant temperature rise when compressed. The aft cap 44 may be welded to a fore cap 49 to hermetically retain argon gas 45. 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.

FIG. 8 graphically illustrates a relationship between the collapse pressure and the sphere wall thickness for a 0.2 inch diameter (0.1 inch radius) sphere formed from plastic with a variable wall thickness. In determining P_crit, E is (the Modulus of Elasticity) about 3×10⁵ and μ is (Poisson's Ratio) about 0.2. The igniter can be designed for the spheres to burst at any desired pressure. An ideal collapse pressure is from 2000 psi to 5000 psi.

FIG. 9 graphically illustrates a relationship between the collapse pressure and temperature of the argon at the collapse pressure. P₁ is atmospheric pressure, nominally 14.7 psi and P₂ is the collapse pressure as noted by the vertical axis of FIG. 9. T₁ is ambient temperature, nominally 500° R (40.3° F.) and T₂ is the argon temperature at the collapse pressure in ° R. N is a gas constant that is 1.67 for argon. The igniter utilizes the leading edge of the pressure wave from the cartridge propellant burn to ignite the sustainer propellant. Features of this igniter include its simplicity, requirement of a single igniter and no timer. Multiple bubbles may be utilized to uniformly distribute both the flame front and the pressure front.

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 .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 FIG. 9. Burn temperature of a typical sustainer propellant is on the order of 6500° F. At that temperature, the Carnot efficiency (a measure of the ability to change heat to mechanical energy) is about 20%, significantly higher than the 14% efficiency for average gun powder which burns at about 4500° F. This means that the Specific Impulse of the sustainer propellant, assuming a well designed nozzle, should be close to 250 seconds at sea level.

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. FIG. 10 illustrates in exploded isometric view, three 120° sabot segments 46 that may be assembled around the bullet. The sabot segments 46 may be formed from a molded composite body, such as carbon or glass filled plastic. A biodegradable plastic may be desired for environmental concerns. Suitable biodegradable plastics include polyglycolide, polyactic acid and poly-3-hydroxybutyrate.

When the aft portion of the bullet includes whiskers, slots 47 are included in the sabot segments 46 to accommodate those whiskers. FIG. 11 is an isometric view of the sabot segments 46 assembled to form a sabot 48 held together by a fore slip ring 50 and aft retention band 51. The fore slip ring restrains the sabot segments 46 and provides a gas seal. Typically, it is formed from a molded nylon, lubricant filled nylon or Teflon (trademark of DuPont of Wilmington, Del. for polytetrafluoroethylene). The fore slip ring can be a continuous band or a plurality of abutting arcuate segments. If the gun barrel is rifled, the fore slip ring has an outside diameter slightly larger than the sabot diameter (SD) to seal the rifling. As the fore slip ring 50 is not bonded to the sabot segments 46 and merely makes a loose friction fit, the high rate of spin imparted to the fore slip ring by the rifling is not imparted to the sabot/bullet. Rather, the sabot/bullet is either imparted with no spin or a slow rate of spin, on the order of 100 revolutions per second (rps).

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.

FIG. 12 illustrates the bullet 10/sabot 48 assembly loaded into a cartridge case 56. The cartridge case includes cartridge propellant 58 that is ignited by a primer 60 when the gun is fired. As best illustrated in the enlarged view of FIG. 13, a pressure front generated by cartridge propellant burn engages aft face of igniter 62 enabling ignition of the sustainer propellant when the desired pressure level is achieved.

FIG. 14 is an isometric view of the bullet 10/sabot 48 assembly in cartridge 56. the fore slip ring is full caliber to engage rifling of the gun barrel, if present. While the bullet disclosed herein may be used with any small caliber gun, preferred calibers include 0.308 inch, 0.338 inch, 20 millimeter, 30 millimeter and .50 caliber.

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.

EXAMPLES

Advantages of the bullet described herein may be better understood by the following prophetic Example:

In the Table illustrated in FIG. 15, various bullet parameters are calculated by analytic methods and compared to properties of conventional bullets. The properties of the conventional bullets were determined by data published by ammunition companies. Significant improvements by the bullets disclosed herein are noted, particularly for muzzle velocity, bullet drop at 1 km and time of flight to target, as well as accuracy.

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, v_axial, 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 v_axial. 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 v_wind, then the total equivalent wind velocity v_new is the vector sum of v_axial plus V_wind. 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 v_new, 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 v_new. This causes a component of the thrust vector to be pointing exactly opposite to that of the side wind v_wind 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.

Claims

1. A sub-caliber bullet having long-range accuracy, comprising: a forward portion, a mid-portion and an aft portion, said aft portion having an outwardly extending feature that contributes to aerodynamic stability;said forward portion being a first material having a first density that is in excess of 10 g/cm3 and both said mid-portion and said aft portion being of a material different from said first material and having a respective density that is less than said first density;said sub-caliber bullet having a length, L, to maximum diameter, D, aspect ratio, L:D, of at least 5:1; anda diameter, d, of said entire forward portion and of said entire mid-portion satisfying an aerodynamic equation selected from the group consisting of Power Law equation: d=D*(x/L)n

2. The sub-caliber bullet of claim 1 wherein n is approximately 0.67.

3. The sub-caliber bullet of claim 2 wherein said forward portion is selected from the group consisting of copper-jacketed lead, tungsten, tantalum, alloys thereof and composites thereof.

4. The sub-caliber bullet of claim 3 wherein said aspect ratio, L:D, is approximately 10:1.

5. The sub-caliber bullet of claim 3 wherein said aft portion has a plurality of outwardly and rearwardly extending whiskers symmetrically disposed about a circumference thereof.

6. The sub-caliber bullet of claim 5 wherein said forward portion is selected from the group consisting of tungsten, tungsten alloys and tungsten composites.

7. The sub-caliber bullet of claim 6 wherein said mid-portion is hollow.

8. The sub-caliber bullet of claim 6 wherein both said mid-portion and said aft portion are made from a composite of glass or carbon.

9. The sub-caliber bullet of claim 6 wherein said aft portion is a reinforced polymer composite.

10. The sub-caliber bullet of claim 3 wherein said aft portion has a plurality of outwardly and rearwardly extending fins symmetrically disposed about a circumference thereof.

11. The sub-caliber bullet of claim 10 wherein said aft portion has a boat tail configuration.

12. The sub-caliber bullet of claim 10 wherein a blind bore extends into said mid-portion from said aft portion.

13. The sub-caliber bullet of claim 12 wherein a propellant selected from the group consisting of sustainer propellant and base-bleed propellant occupies said blind bore and an igniter is in flame communication with said sustainer propellant.

14. The sub-caliber bullet of claim 13 wherein said igniter includes at least one gas-filled frangible sphere, said frangible sphere having a wall thickness effective to burst at a desired pressure.

15. The sub-caliber bullet of claim 10 wherein said forward portion is selected from the group consisting of tungsten, tungsten alloys and tungsten composites.

16. The sub-caliber bullet of claim 15 wherein said mid-portion is hollow.

17. The sub-caliber bullet of claim 15 wherein both said mid-portion and said aft portion are made from a composite of glass or carbon.

18. The sub-caliber bullet of claim 15 wherein said aft portion is a reinforced polymer composite.

19. An ammunition round including a sub-caliber bullet having long range accuracy, comprising: a cartridge case filled with a cartridge propellant and having a bullet/sabot assembly partially inserted into an open end thereof:said sabot having a full caliber forward portion with a length effective to support said bullet; andsaid sub-caliber bullet having a forward portion, a mid-portion and an aft portion with said aft portion having an outwardly extending feature that contributes to aerodynamic stability and said forward portion being a first material having a first density that is in excess of 10 g/cm3 and both said mid-portion and said aft portion being of a material different from said first material and having a respective density that is less than said first density, said sub-caliber bullet having a length, L, to maximum diameter, D, aspect ratio, L:D, of at least 5:1 and a diameter, d, of said entire forward portion and of said entire mid-portion satisfying an aerodynamic equation selected from the group consisting of a Power Law equation: d=D*(x/L)n

20. The ammunition round of claim 19 wherein said sabot is formed from a plurality of segments held together by at least one slip ring that circumscribes said forward portion of said sabot and engages said sabot in a loose friction fit.

21. The ammunition round of claim 20 wherein said aft section of said bullet has a plurality of outwardly and rearwardly extending whiskers symmetrically disposed about a circumference thereof.

22. The ammunition round of claim 20 wherein said Power Law exponent, n, is approximately 0.67.

23. The ammunition round of claim 20 wherein said aft section of said bullet has a plurality of outwardly and rearwardly extending fins symmetrically disposed about a circumference thereof.

24. The ammunition round of claim 23 wherein a blind bore extends into said mid-portion from said aft portion and a propellant selected from the group consisting of sustainer propellant and base-bleed propellant occupies said blind bore with an igniter is in flame communication with said sustainer propellant.

25. The ammunition round of claim 24 wherein said igniter is effective to ignite said sustainer propellant after said bullet exits a gun muzzle.

26. The ammunition round of claim 25 wherein said igniter includes at least one gas-filled frangible sphere, said frangible sphere having a wall thickness effective to burst at a desired pressure.

27. The sub-caliber bullet of claim 23 wherein said aft portion has a boat tail configuration.