PRINCIPLES OF GUNNERY. 
47 
CHAPTER III. 
Explosion and Pressure in the Bore of a Gun. 
Explosion of Gunpowder.—Explosion of Gun-cotton.— Comparison of tlie Results of Explosion of 
R.L.G. and P. Powder.—Objects sought after by the use of Powder as a Propelling Agent.— 
Causes which affect the Time of Explosion of Powder.—Different Powders required to give 
the best Results in Light and Heavy Guns.—Effect of Explosion in the Bore of a Cun.— 
Experiments with the N oble Chronoscope.—Crusher Gauge.—Manner of Explosion of Powder 
in a Gun.—Resistance to the Motion of a Projectile in the Bore of a Gun.—Resistance to the 
Motion of Translation.—Resistance to the Motion of Rotation.—Resistance due to Friction.— 
The Maximum Limit of Pressure allowable in the Bore of Heavy Guns. 
The principal advantage of gunpowder, over gun-cotton and other Explosion 
explosive substances for use with ordnance, is its comparatively slow powder, 
explosion. 
The progressive nature of the explosion of gunpowder allows of a 
certain interval of time to elapse before the maximum pressure of the 
gas is exerted in the bore of the gun. The projectile then has time to 
move, and consequently begins to move while the powder is exploding; 
so that an increasing space is provided for the rapidly expanding gas, 
which changes the character of the force exerted by the gas more into 
the nature of a pressure than an impulse. 
An impulse is theoretically an indefinitely large force acting abso¬ 
lutely instantaneously; and although, strictly speaking, there are no 
forces in nature which answer to the above definition, yet there is a 
close approximation to it in the detonation of gun-cotton and other 
explosive substances. 
It is this approximation of the force of exploded gun-cotton to that Explosion 
of an impulse which renders it (in its present state) unfit for general Attorn 
use in the service of ordnance, straining as it does inordinately both 
projectile and gun. 
In quick-burning powders, such as R.L.G., a shorter interval of Oomparf* 
time elapses before the maximum pressure of the charge is exerted resuitsof 
than in slow-burning powders like P. powder. of r°l 0 g. 
The time of explosion has an important effect on the maximum pres- andP. 
sure in the powder-chamber. As the time of explosion increases; this pow 61 ’ 
pressure diminishes, and vice versa. 
From recent experiments with P. and R.L.G. powders in the bore 
of a 10-in. rifled M.L. gun of 18 tons, it was calculated that the time 
elapsed^ before the maximum pressure was exerted in the bore, was 
with the (slow-burning) pebble powder *00437 sec., and with the (quick¬ 
burning) R.L.G. powder *00070 sec.* The maximum pressure of the 
P. powder was about 18 tons on the square inch; being considerably 
less than that exerted (22 tons) by the R.L.G. powder. ( Vide Plate L) 
* Vide “ Researches on Fired Gunpowder,” by Capfc. A. Noble, F.R.S., and Professor Abel, 
F.R.S., p. 118. 
