50 
PRINCIPLES OE GUNNERY. 
Different In different natures of ordnance, where the charge and calibre vary 
reared to considerably, great attention must be paid to the regulation of the 
Kresults s i ze an( ^ density of the grains of the powder employed, in order to 
in light and ,pansmit the maximum of muzzle energy to the proiectile with the 
heavy guns. . . pit , , A , • , f 0 . . ., 
minimum oi local pressure on the gun. A light projectile moves 
easily, and a quick-burning powder is found most suitable; a heavy 
projectile moves less easily, and a slow-burning powder is found most 
suitable. 
Effect of When a charge of powder is exploded in a gun, a large quantity of 
inthebOTogas is generated, which rapidly expands, and exerts an enormous 
of a gun. p ressure "both on the chamber of the gun and on the base of the 
projectile. This pressure is usually measured in foot tons on the 
square inch. (Fide p. 38.) 
The pressure on the base of the projectile continually varies while it 
is in the bore of the gun (vide Pressure Curves, Plate I.), reaching a 
maximum a short time after the projectile has moved; then it gradually 
decreases towards the muzzle. The effect of this pressure on the base 
of the projectile is to give velocity to the projectile, which continually 
increases towards the muzzle, where it is the greatest, and it is then 
called the muzzle velocity. 
There is a corresponding pressure on the chamber and bore of the 
gun; as at any given instant of explosion the pressure of the expanding 
gases may be supposed equal in every direction— i.e., on the base 
of the projectile and on the walls of the bore. The pressure of 
fired gunpowder in the bores of guns has been very fully inves¬ 
tigated by the Committee on Explosives, ! under the presidency of 
Colonel Younghusband, R.A., F.R.S. ; and Retails of experiments are 
given in the Progress Reports published from time to time by that 
Committee. By means of the Noble chronoscope and the crusher 
gauge (for details of which vide App. I.), the pressures in a gun at 
any part of the bore, and the corresponding velocities of the projectile 
in the bore, can be ascertained. 
ruentswith chronoscope measures the time occupied by the projectile 
the Noble in passing over certain known intervals in the bore of the gun. The 
scope?" velocity of the projectile at any part of the bore is thus determined, 
and thence the pressures necessary to produce such velocities are 
calculated. 
The results are plotted off on a diagram to scale. (Vide Plate I.)* 
The horizontal distances at the bottom of the plate represent the space 
in feet traversed from the seat of the projectile to the muzzle of the 
gun. The left-hand vertical column represents a scale of pressure in 
tons per square inch, or corresponding pressure in atmospheres; the 
right-hand vertical column represents a scale of velocity in feet per 
second. 
Plate I. shows the result of an experiment made with pebble and 
R.L.Gr. powder to determine the pressure and velocity given by them 
respectively in the bore of a 10-in. M.L, gun, when firing a 300-lb. 
* Vide “ Researches on Pired Gunpowder,” Plate XIX. 
