POWDER 73 



as remarked, by a deep and extremely tight turnover 

 of the case. Any of the foregoing excesses will have 

 the effect of substantially increasing the initial pressure, 

 the pressure at the breech-end of the barrel, set up 

 at first impact of explosion. In this connection I may 

 remark that a high shot-velocity is not a necessary 

 corollary of a high breech-pressure. A good powder, 

 properly loaded, will not exhaust its energies within 

 the breech of the gun, but will continue to evolve 

 and expand its gases from that point right up to the 

 muzzle of the piece. 



Diameter of bore has a considerable bearing on this 

 question of powder pressures. The smaller the bore 

 the greater the pressure, other things being equal. 

 This, partly by reason of the closer confinement of 

 the powder and also by the fact that the elongation 

 of the column of shot excites greater frictional resist- 

 ance. A service-charge of powder may generate a 

 safe working pressure of about three tons per square 

 inch in the breech of a 12-bore shot-gun. With pro- 

 portionate charges in 16, 20, and 28-bores, this pressure 

 may be considerably exceeded without overstepping 

 the bounds of safety ; this, by reason of the fact that 

 the restricted internal area of these guns provides less 

 ground for the heightened pressure to play upon. 

 Smokeless powders show greater sensitiveness with 

 regard to their ignition than do black powders gener- 

 ally ; and, as remarked, the breech pressures generated 

 by the former can be increased or diminished to some 

 extent by varying the force or intensity of the detonat- 

 ing flash. Lengthy exposure to the sun or heat of 

 any kind may have the effect of drying a powder 

 sufficiently to cause it to develop undue or even 



