PRINCIPLES OF GUNNERY. 
51 
projectile with battering charges— i.e., with 70 lbs. P., or 60 lbs. R.L.G.* 
The continued curves show the results with P. powder, and the 
dotted curves those with R.L.G. powder. From this diagram the 
pressure and velocity may be seen by inspection at any part of the bore 
of the gun. By comparing the pressure curves, the advantage of P. 
over R.L.G. powder is well shown. The maximum pressure in the 
gun in each case is represented by the vertex of the curve, and the 
work done on the projectile is represented by the respective areas 
enclosed by the curves. The area of the P. pressure curve is greater 
than that of the R.L.G. pressure curve, while the vertex is lower; 
which indicates that the muzzle energy of the projectile is greater, and 
that the maximum pressure in the gun is less, when the P. powder 
charge is fired instead of the charge of R.L.G. powder. 
Another method of determining the pressure in the bore of a gun is 
by means of the crusher gauge. [Vide App. I.) This is done by direct 
measurement, and is a rougher method of approximating to the true 
pressure than that by the chronoscope. However, the pressures calcu¬ 
lated from chronoscopic experiments and those observed directly by 
means of the crusher gauge agree very closely, when slow-burning 
pebble powder is used; but when a quick-burning powder like R.L.G. 
is used, the agreement is not so close, owing to the intense local action 
which is set up in the combustion of such powders, which produces 
anomalous local pressure in the chamber of the gun.f 
Generally speaking, then, the chronoscope measures the mean pressure 
and the crusher gauge the local pressure in the powder-chamber; and 
by the combined use of both these methods of experimenting, practical 
results of the highest utility have been arrived at. 
When a gun is fired, the charge of powder is very rapidly exploded, 
and practically (so far as useful effect is obtained from its combustion) 
explosion may be supposed to be completed when the maximum pressure 
is obtained. Some portion of the charge, no doubt, is ignited during 
the after passage of the projectile to the muzzle, and is blown out 
of the gun only partially exploded, more especially when battering 
charges of P. powder are fired; but the useful effect of this after 
combustion is only a small per-centage of the whole. It must not 
be supposed that the powder does comparatively little work after the 
maximum pressure has been attained: it is quite the contrary; but 
only that, practically, explosion is completed in a very short space of 
time. An inspection of the diagram (Plate I.) shows the general con¬ 
ditions of explosion very clearly. The maximum pressure in the 
powder-chamber was in this instance attained with R.L.G. powder 
when the projectile had moved T V hs of an inch; with P. powder when 
the projectile had moved 6 ins. The powder, then, is not instanta¬ 
neously exploded ; but supposing the explosion to be practically com¬ 
pleted when the maximum pressure is reached, it will be seen by 
in 
* Vide Table showing Results of Explosion, &c., of P. and R.L.G. (p. 48). 
f For information on this point, vide a paper by Major Morgan, R.A., late Assistant Super¬ 
intendent Royal Gunpowder Factory, Waltham Abbey, on “ The Determination of the Explosive 
Force of Gunpowder.” ( <c Proceedings, R.A. Institution,” Vol. VII. p 430.) 
