Efficiencies of Gun System and Charge

Two parameters, that is, piezometric efficiency and ballistic efficiency are commonly employed in order to evaluate the overall performance of a particular gun-charge-projectile system and are defined in the following manner. 

Piezometric efficiency Piezometric efficiency is defined as the ratio of the mean pressure and the maximum breech pressure. The mean pressure is taken as that pressure which, if uniformly exerted upon the projectile over the entire length of the bore, will produce the observed muzzle velocity. Thus (Equation 4.2)  

In general, the pressure-travel curve becomes flatter with higher piezometric efficiency. 

2) Ballistic efficiency Ballistic efficiency is defined as the ratio of the total work done upon the projectile to the total work potential of the propelling charge, that is, (Equation 4.3)  

A high ballistic efficiency can be obtained by burning the propellant charge as early as possible in the projectile s traverse of the gun bore thereby reducing residual muzzle pressure. 

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