1918] on Internal Ballistics 309 



The gas pressure at the moment the band is fully engraved is 

 given by the formula 



pr- 



-"' = 1'' 



where Jc' is the constant for driving band resistance, z^ the fraction of 

 the charge burnt, and Vo the specific volume of the charge when the 

 shell has moved a distance in the gun sufficient to engrave the band. 

 x\s in the previous argument, if no more of the charge was burnt 

 expansion of the gas would take place and further work would be 

 done on the projectile according to the relation 



p {v - ay = Jc' zl, a constant. 



Thus at any expansion volume v we must always include the 

 term Jc' zl as well as the usual term Jc z\ 



It can be easily proved that at any position up to the point 

 where s - 1, that is when all the explosive is burnt, the mean 

 pressure of the gas 



where K - | - 1 - 0*22121, and Jc - 66-0. 



fC 



By combining this equation with the differeatial equation of 

 motion, certain formulas are obtained which enable the motion of 

 the shot in the gun and the pressure of the gas to be plotted as 

 shown in Fig. 2. 



[A. G. H.] 



Vol. XXII. (No. 112) 



