THE EFFECT OF THE OPTIMUM CHAMBRAGE ON THE MUZZLE VELOCITY OF GUNS WITH A QUALITATIVE DESCRIPTION OF THE FUNDAMENTAL PHENOMENA OCCURING DURING GUN FIRING

A qualitative description is presented of the effect of chambrage, the increase in cross-sectional area from the barrel bore to the propellant chamber. The effects of the other fundamental factors which determine the pressure behind a projectile are discussed including the propellant burning, the presence of the breech end, and the accelerating projectile motion. The description is given in terms of the rarefaction and compression impulses which are present in the propellant gas during the firing of a gun. In ballistic calculations, chambrage is treated by assuming that the actual chamber can be replaced by an equal volume chamber of cross-sectional area equal to that of the bore. This method of treatment may be in error. The possible size of this error is indicated by a calculation of the muzzle velocity of a gun with an optimum condition of chambrage which is approached by a gun with either a large, well- shaped chamber or with a propellant burning at the proper rate in a smaller chamber. The muzzle velocity of the optimum chambrage gun is shown to be as much as 28% greater than that of the comparable constant-diam gun.