Ammunition and explosives – Cartridges – Projectile structure
Reexamination Certificate
2001-12-15
2004-01-20
Poon, Peter M. (Department: 3643)
Ammunition and explosives
Cartridges
Projectile structure
Reexamination Certificate
active
06679178
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
This invention relates to firearm systems having a barrel and particularly to smooth bore barrel system and ammunition that is achieving stability in flight by spinning the projectile.
2. Description of the Prior Art
The predominant group of the breech loaded contemporary weapons has helical rifled barrels. The purpose of rifling is, by having a close fit, to spin the projectile along the barrel and to give the projectile stability during the exterior ballistic, provided by gyroscopic effect. The rotation is around the main axis of the projectile and the barrel. Low rotation speed leads to less stability, very high rotation speed leads to, so called “nose up”-effect, otherwise the axis of the projectile crosses trajectory of exterior ballistic. Therefore the pitch of the rifling has to be carefully considered upon the range and the purpose of the projectile. The conventional projectile has a part of its surface (or jacket) that is slightly oversize or interference fit with regard to the bore diameter of the barrel of the weapon with which it is used. The surface (jacket) of the projectile is getting squeezed and engraved during the passage down the barrel of the weapon by the helical rifling grooves in the barrel. The projectile is spun by the rifling grooves to stabilize its flight as explained hereinafter. Considerable portion of the energy produced by the propellant is lost by the process of squeezing and engraving and by the dry friction between the projectile and rifled barrel along the acceleration. Engraving and friction not only consume the energy of the propellant but also transfer the kinetic energy once gained by hot propellant gases, again to heat. The friction and heat are serious problems especially for automatic or high caliber weapons, causing fast barrel erosion and loss of external ballistic properties—range and accuracy. Thermal enlargement of the bore barrel also leads to uncontrolled loss of pressure fit and less muzzle velocity affecting the same way exterior ballistic properties.
In order to reduce the negative effects of engraving and friction, several different approaches are established as state-of-the-art. Wide spread approach to reduce the dry friction is to put the projectile into a plastic cylindrical body (sabot) engaged with the projectile surface until both leave the muzzle thereby using friction plastic/metal instead of metal/metal and reducing the friction. Many patents used this approach so the patents cited herein: U.S. Pat. No. 3,847,082 issued to Feldmann F.; U.S. Pat. No. 3,769,912 to Friend W. H.; U.S. Pat. No. 4,063,511 to Bisping B. and they are cited here only as representative examples. A large variety of patents exploit similar approaches. Common and overwhelming drawbacks of introducing a sabot is the use of soft material preferably plastic, which decreases very fast its mechanical properties with increase of working temperature (especially in automatic weapons) and leads literally to smear the surface of the sabot along the barrel. Another disadvantage relates to the energy used to accelerate the sabot, which is not part of the projectile in flight, therefore the heavier the sabot—the bigger the loss of energy. One more disadvantage is that the projectile is always subcaliber compared to the full bore diameter with proportional reduction of the load.
Another approach is to use completely smooth bore barrel and a different means of providing the projectile with revolving momentum. One of them—U.S. Pat. No. 4,386,747 to Kuhl R. D. is using ammunition with means for self-generated revolving momentum.
A toroidal mass is disposed inside the projectile and attached and secured to the projectile by means of bi-convex spring or similar flexible structure so that the mass is setoff in oscillation upon the sudden acceleration due to the firing of the projectile. There are several drawbacks of this solution: the system is usable only for comparably big caliber weapon; a sufficient part of the weight and free volume of the projectile is used to accommodate the structure of toroidal mass, and bi-convex spring; an important part of the mass and volume of the projectile is engaged to provide revolving momentum; the relative density of the projectile is reduced.
Another direction is using only the smooth bore barrel to provide the conventional projectile with revolving momentum as in U.S. Pat. No. 4,841,657 to Mossberg A. I. The system is using axially rotating barrel moved by the force of expanded gases. The axially rotating barrel is engaged with the projectile surface whereby to impart rotary motion to the projectile. This system has to respond to controversial requirements. In order to provide revolving momentum to the projectile the barrel has to have a good grip with it. This defeats one of the main purposes of the smooth gun barrel—reducing the friction and friction-related erosion The increased grip will lead to increase of the temperature and thermal enlargement of the barrel. An enlarged barrel cannot provide a good grip thereby cannot provide a repeatable revolving momentum and will lead to significant lost of gas pressure.
Another disadvantage is that a big part of the propellant energy will be consumed for moving comparably big mass of the barrel, back, forward and around the axis with appropriate velocity. U.S. Pat. No. 4,176,487 issued to Manis J. R. teaches a system comprising a smooth bore barrel with annular grooves or pockets in the bore-walls which act as propellant gas pressure relief areas. When the projectile is fired, the helical notches on its rear part interact with the gas pressure relief areas or spaces of the bore, allowing the propellant gas to be expanded through the rear helical notches imparting a twist to the projectile. The system uses mutual interaction between specially designed bore barrel (referred as smooth bore barrel, despite a number of annular chambers along the barrel) and ammunition with rear helical notches. The drawback of this system is that the stress-point of each annular chamber reduces significantly the mechanical properties of the barrel. The difficulties of manufacturing and especially of cleaning such barrel from the products of propellant burning are another disadvantage. When in flight the helical notches will interact with air, imparting to the projectile an inverse directed twisting motion, therefore reducing the initial revolving momentum and abating the external ballistic properties.
There are two different parts of the barrel largely exposed to erosion. First one is breech part neighboring the cartridge nest, where the action of high temperature and high-pressure gases is combined with the process of engraving the projectile and dry friction. The second one is, before and at the muzzle, where the dry friction is combined with highest velocity of the projectile.
A very early notion of minimizing the erosion from the burning propellant and engraving is carried in the U.S. Pat. No. 37,193 to Alsop C. R. The patent suggests attaching a rifled section to the muzzle of smooth bore barrel thereby gaining a high speed and decreasing the erosion of hot gases at the breech section. The rifled section is engraving the projectile and giving to it revolving momentum. The patent admits that the rifling is imparting a considerable friction and transmitting substantial heat to the projectile, but those problems are said to be overcome by gained momentum of the projectile. The rifled section was suggested as a gradual reduction in diameter of the bore progressing away from the breech and into the rifled section. The length of the rifled section is proposed to be 2 to 3 inches. The rifled section has to be mounted to the main barrel by threaded connection with thread direction opposite to the rifling.
Despite the drawbacks of this concept, it was revitaized recently in U.S. Pat. No. H0001365 to Amspacker M. R. The concept reduces unacceptable erosion of the breech section. The gun barrel comprises a smooth bore breech section and a longer gain twist rifle
Mihaylov Gueorgui M.
Mihaylova Evdokia K.
Parsley David
Poon Peter M.
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