1. Field
The present invention relates to barrels for guiding a projectile through an internal bore, and, more particularly, to a gun barrel having a vent chamber.
2. State of the Art
In a typical barrel, a projectile such as a bullet is typically "fired" from a case by propelling the bullet through the barrel by a propellant. Although gunpowder is typical, other propellants may be used such as compressed gases. A tight seal is formed between the barrel and the bullet to prevent escape of propellant past the bullet.
Effective stoppage of the propellant gas within the barrel is referred to as obturation. Obturation, as generally used with regard to ordnance, refers to the function of the two enclosing seals that trap propellant gas within a gun's barrel and chamber. For a typical rifle, the two gas-tight seals are the closure of the breech by an expanded case supported by a locked bolt and the seal between the bullet and the barrel rifling. That is, in the firing of a rifle, typically the high-pressure gas formed by the burning propellant is obturated by a brass case which expands and seals tightly against the chamber walls and by a portion of the soft outer jacket of the bullet which deforms against the surfaces of the barrel rifling. Obturation is lost as the bullet exits from the muzzle and gas escapes from the barrel. This coincides with the "bang" emitted by the gun.
For a typical weapon, the ejected gas is at very high pressure and temperature which leads to formation of an underexpanded supersonic flow field near the muzzle. This supersonic flow has a higher velocity than the bullet and at first overtakes and passes the bullet.
As the gas expands outward from the muzzle, the gas velocity decreases to subsonic velocity behind the advancing shock front. Turbulent shear mixing occurs between the supersonic stream and the surrounding atmosphere, forming a combustible mixture with the fuel-rich propellant gas. Although the pressure in the expanding gas is comparatively low, the temperature in the associated shock waves is comparable to the temperature of the gas inside the muzzle, and often above the ignition temperature of the gas stream. As a result, a second explosion of the propellant may occur after it has left the barrel. The second explosion may release as much energy as the initial burn of the propellant and far more noise. The atmospheric combustion or second explosion produces the luminous muzzle flash and muzzle blast over and above the normal gun report.
As a projectile leaves the barrel, it typically passes through a reversed turbulent flow, one or more shock fronts, and possible atmospheric explosions. These phenomena may degrade the accuracy of the weapon as well as cause harm to people nearby. All of these effects are related to the remaining gas in the barrel at loss of obturation. Muzzle brakes, silencers, and other devices which discharge the propellant gas at the muzzle or through ports to the atmosphere merely change the time and location for loss of obturation and do not mitigate the undesirable effects.
The pressurized propellant gas may be created in a variety of ways. In some low-energy devices such as pellet guns, air may be compressed into a chamber by a hand operated pump. When the trigger of the gun is operated (e.g., pulled), a valve is opened. In turn, the pressurized air (or gas) is released into one end of the tube or barrel behind the pellet, which is thereby accelerated through the barrel. As the pellet accelerates, the pressurized air expands and its pressure decreases.
In high energy devices, pressurized gas is created by igniting a propellant such as gun powder. A projectile such as a bullet is placed between the propellant and the throat of the barrel. Upon combustion of the propellant, a high-pressure gas is formed very rapidly to accelerate the bullet from the throat down the length of the barrel toward the muzzle. Typically, gas formation is substantially complete before the projectile exits the barrel.
In a typical gun, peak gas pressure is achieved before the projectile has traversed one-fifth of the distance through the bore. Accordingly, gas pressure is reduced considerably by further expansion when the projectile has reached the end of travel within the barrel. For example, in a high-powered sporting rifle, the peak pressure may be approximately 50,000 pounds per square inch. In contrast, just before the bullet exits the barrel, the pressure typically has declined to about 10,000 pounds per square inch. The bullet, however, accelerates throughout the entire length of travel in response to the pressure profile. Typically, more than 80% of final velocity is achieved by the midpoint of travel in the barrel. At 90% of travel, 98% of muzzle velocity has typically been reached.
In those arrangements where an effective seal is formed between the projectile and the barrel wall, the gas pressure is still considerable as the projectile reaches the muzzle. Obturation ends as the projectile leaves the tube and a pressure wave issues from the muzzle around the base of the projectile. The gas of the gun muzzle wave or blast at first, just outside the muzzle, is traveling faster than the bullet, causing an unstable environment for a short distance. Accuracy of the weapon may thereby be adversely affected. For example, any imperfections in the base of the bullet can create an uneven pressure profile across the base of the bullet and in turn affect the trajectory. Similarly, imperfections in the muzzle crown can misdirect the gas wave or introduce turbulence to disrupt the bullet trajectory.
In large weapons, the gas wave or blast may cause dust, dirt, and the like to be thrown into the air. The result may be obscured vision and other problems associated with airborne dust and grit. Further, the muzzle flash is due in part to incandescence of hot gas as it emerges from the gun and by secondary combustion of the propellant gas after mixing with oxygen in the atmosphere. The muzzle flash can interfere with vision and can otherwise be harmful.
To regulate or control gun recoil and jump, ported barrels have been employed. In a ported barrel, a port or aperture is disposed in the wall of the barrel to allow propellant gases to ventilate through the side of the barrel before the projectile exits the barrel. The gas escapes directly to the atmosphere through the port so that obturation ends. Based on the size of the port, the recoil and muzzle jump can be controlled. Recoil compensators such as the parted barrel diminish the forward momentum of the propellant gas by deflecting it radially from the muzzle. The lateral discharge of gas from a recoil compensator, however, causes an undesirable increase in noise and blast effect.
Ported barrels may also be used to reduce the report or sound as the bullet exits the muzzle. As shown in U.S. Pat. No. 4,501,189 (Brandl, et al.), a port is formed in the barrel near the chamber for the purpose of dissipating propellant energy before the bullet has achieved full velocity. Bullet velocity is thus restrained to less than atmospheric sonic velocity. A chamber for receiving the discharged gas is connected to the port. The ported barrel construction of Brandl, et al., however, does not serve to silence muzzle blast. To regulate the blast, a muzzle-mounrws silencer is to be used because gas pressure remains somewhat high at the time of bullet exit from the muzzle.
As known, muzzle silencers, such as the one shown in U.S. Pat. No. 3,776,093 (Leverance, et al.), may be attached at the muzzle end of the barrel. No modification of the barrel is typically required other than to provide a means of attachment. Muzzle silencers effectively reduce the sound of weapons even though the muzzle blast is still of full force. That is, the pressure has not been reduced prior to loss of obturation at the muzzle. Indeed, the effect of muzzle blast on the bullet when using a silencer is frequently worse than without the silencer. The bullet in free flight must travel through the turbulent gas in the silencer. In turn, the silencer may adversely affect accuracy.
Several other factors which affect the accuracy of a gun are barrel stiffness, barrel weight, and uneven heating of the barrel. Accuracy is typically degraded by flexure of a gun barrel during firing. A major purpose for barrel thickness and consequent weight is to provide added stiffness to improve the gun's accuracy. Barrel weight may also be increased to reduce recoil and "barrel jump," and to promote more even heating of the barrel during heavy use. Uneven heating of a gun barrel during rapid firing can cause distortion of the barrel and affect accuracy.
There remains a need for a gun barrel construction which reduces many of the deleterious effects from muzzle blast, inadequate barrel stiffness, and uneven heating of the barrel.