Gun Barrel Optimized for Supersonic Projectiles

Abstract

This patent is for an apparatus which increases the muzzle velocity and energy of a supersonic projectile for a given set of ballistic conditions. When a projectile is fired from a barrel, there is typically a great deal of available energy still remaining in the combustion gas. This energy is released from the muzzle without being used when the projectile exits. Friction between the barrel and projectile, and the length, cost, and weight of the barrel limit the amount of energy which can be transferred into the projectile. This apparatus may constitute an attachment to the end of a pistol, rifle, or other gun; it may be a modification to the barrel of a gun; or it may be incorporated into an entirely new barrel for a gun. The apparatus consists of a non-contact section, and a diverging section followed by a straight, constant area section, and optionally followed by a short converging section. The apparatus works by providing the optimal geometry for the air in front of the projectile to exceed sonic velocity. The sonic shock wave is then moved out in front of the device, which reduces the air pressure at the front of the projectile and increases its acceleration. Additionally, as the projectile enters the device it loses physical contact with the walls so friction is eliminated. With a supersonic projectile, the combustion gas behind it must travel at supersonic speed to move around and past the projectile and this produces very large wave drag. So even though there is not a tight seal between the projectile and the wall, the expanding gas still exerts considerable accelerating force on the projectile. Also, the gas that does flow around the projectile produces a hypersonic jet of air exiting the device ahead of the projectile, in effect blazing a trail through the air for the projectile to follow. Furthermore, in the non-contact section the wall friction is negligible while the fluid friction is significant which causes the projectile to absorb more available energy from the propellant.

The claims for this patent are: 
     
         1 . an apparatus through which a projectile is accelerated, which does not have constant cross section throughout its length; 
     
     
         2 . where the apparatus in  1  increases the projectile velocity, improves the accuracy, reduces the barrel weight, reduces the barrels angular moment of inertia, reduces the barrel cost, improves the barrel lifetime, or any combination of these; 
     
     
         3 . the apparatus in  1  may be either an added on device to an existing gun barrel or may be a section specially machined or constructed into the end of a gun barrel; 
     
     
         4 . the apparatus in  1  may be constructed either during the original manufacture of the barrel, or may be a later modification to an existing barrel; 
     
     
         5 . where the change in cross sectional area of the apparatus in  1 , separates the barrel length into a contact zone and a non-contact zone; 
     
     
         6 . where the change in cross sectional area is designed to accelerate the gas exiting the muzzle to supersonic speed; 
     
     
         7 . where the supersonic gas flow in  6  reduces the aerodynamic drag experienced by the projectile at the end of the barrel and the beginning portion of its free flight. 
     
     
         8 . where the absence of friction in the non-contact zone of  5 , and the reduced air resistance of  7  cause the projectile to achieve higher velocity; 
     
     
         9 . where the material of construction for the non-contact zone may be different from the contact zone, and is selected to reduce weight, reduce cost, increase stiffness, or improve the thermal behavior compared to the material used in the contact zone. 
     
     
         10 . the device has a diverging section designed to reduce the air pressure in front of the projectile while it is still in the barrel;
 a. the non-contact zone and diverging section may be any fraction of the total length of the device, from very small to very large   b. the non-contact zone and diverging section may be designed to optimize projectile velocity, projectile stability, weight of the device, manufacturing cost, or any other variable   
     
     
         11 . the device has a straight section of essentially constant area through which the projectile travels at hypersonic velocity, without contacting the walls
 a. the boundary layer in the straight section provides aerodynamic support to the projectile, stabilizing its path without the projectile actually contacting the wall surface.   b. the straight section may contain surface features designed to control the boundary layer which may include: co-rotational or counter-rotational rifling, labrynth seals, hatching, circumferential grooves or ridges, longitudinal grooves or ridges, any other feature which is shown to assist with achieving  claim 1 ,  2 ,  6  or  8 .   
     
     
         12 . the device may have an optional converging section at the end which reduces the gas velocity to near the projectile velocity (because the gas is moving supersonically a converging section reduces speed and increases pressure); 
     
     
         13 . the dimensions of the device are calculated and optimized for a specific gun, projectile, and other ballistic properties. The dimensions may be optimized using computational fluid dynamics (CFD), by trial and error, by hand calculations or other procedure. 
     
     
         14 . the device produces a hypersonic jet of gas in front of the projectile which moves the shock wave to some distance in front of the muzzle or which reshapes the shock wave to minimize effects on the projectiles velocity when it exits the barrel, or which minimizes the imbalanced forces which tend to destabilize the projectile; 
     
     
         15 . the materials of construction in  9  may be metal, polymer, composite, ceramic or some combination of materials
 a. the material may be selected to improve heat dissipation from the barrel 
 b. the material may be coated with a thermal barrier coating to reduce cooling of the propulsion gasses; 
 c. the material in the non-contact zone need not be wear resistant, and therefore may reduce the cost or weight of the barrel assembly; 
 d. the material may have better machinability, lower cost, better strength/weight ratio, or be compatible with low cost manufacturing methods such as drawing, rolling, sintering, or injection molding. 
 
     
     
         16 . the device may be integral to the barrel or attached to the barrel by threads, set screws, friction fit, adhesive, magnets, tape, or any other means and may be permanently attached or removable. 
     
     
         17 . the device may have the additional benefits of reducing recoil, report, muzzle flash, or other objectionable side effect of firing the gun.