:^>04 Lieut.-Colonel A. G. Hadcock [May 24, 



(2) The pressure rises and forces the copper driving band which 

 surrounds the projectile to give rotation into the rifling grooves. 



(3) The charge still burns, and the pressure forces the shot along 

 the gun. 



(4) The charge is completely burnt. 



(5) By the expansion of the hot powder gases, the shell is forced 

 further along the bore and out of the gun. 



One of the most important of these processes is the forcing of 

 the driving band into the rifling, and the subsequent behaviour of 

 the charge depends greatly on the initial resistance of the driving 

 band when it is forced into the rifling grooves. The greater this 

 resistance, the larger will be the proportion of the charge burnt 

 before the band is fully engraved, and the higher will be the pres- 

 sure when the band is fully engraved. 



Noble and xA^bel, in their original paper read before the Royal 

 Society in 1H75, gave a most important law which governs the 

 relation between the density of the charge and the maximum pressure 

 produced in a closed vessel. This law, formulated from the results 

 obtained by experiment with black powder, still holds closely for all 

 modern powders. 



The law as originally stated is 



'■ 1 - aA 



where p is the pressure in tons per square inch, R constant found by 

 experiment, and A the gravimetric density of the charge. This 

 gravimetric density is an artillery term, but it simply means the 

 specific gravity of the charge as compared with water, supposing it to 

 be spread uniformly throughout the volume of the vessel. It is 

 based on the Act of Parliament gallon of 10 lbs. of water at G2° F., 

 which should occupy a space of 277*8 cubic inches, or 1 lb. of water 

 should occupy 27-73 cubic inches. Thus if C is the capacity in 

 cubic inches of the vessel, and iv the weight of the charge in pounds, 







then the weight of water the vessel would contain is ' — pounds, 



27-73^ ' 



and the gravimetric or specific density, i.e. the ratio of the weight 

 of the charge to the weight of water the vessel would contain, is 



27-73 ?z' 



C 



If we consider the volume occupied by w lbs. of water as the 

 unit of gravimetric or specific volume, then the number of such 

 volumes in our closed vessel or in a gun of capacity C is 



. = 1 = '' 



A 27-73//' 

 so that V corresponds in a gun to a definite length of travel of the shot. 



