PRINCIPLES OP GUNNERY. 
59 
The nature of powder employed exercises a considerable influence Nature of 
on the muzzle velocity. With guns firing comparatively small powder * 
charges, the highest velocity is obtained by using a quick-burning 
powder—such as R.L.Gr. powder; but with guns firing large charges, 
the highest velocity (consistent with safety) is obtained by using a 
slow-burning powder—such as cubical pebble. 
It will be seen from what has been stated (p. 56), that, for a given weight of 
charge, the muzzle velocity of the projectile varies approximately in- P r °j ectilo ‘ 
versely as the square root of its weight. 
The internal space for the expansion of the powder charge in a gun Length of 
of given calibre depends on the length of bore, and increases propor- bore * 
tionately with the length of bore. Since the useful effect of the 
charge of powder depends (vide table, p. 55) on the number of expan¬ 
sions of the powder charge in the bore of the gun, it is evident that 
more work is done, and consequently a greater muzzle velocity com¬ 
municated to the projectile, by a given charge of powder in a longer 
than in a shorter bore. Practically, the length of bore is limited by 
the necessary limitation of the weight of the gun for its particular 
service, and in field and siege guns by travelling conditions; so that 
it is not advisable to exceed certain limits. 
Lengthening the bore of a gun not only gives a higher muzzle 
velocity for the same internal strain on the chamber, but permits of 
the use of a slower-burning powder; causing less strain on the gun and 
carriage—which latter is a point of great importance, not only with 
heavy guns, but also in connection with field and siege artillery equip¬ 
ment. The strain on the interior of the gun is communicated through 
the trunnions and elevating screw to the carriage; so that the less the 
maximum strain exerted on the gun, the less will be the maximum 
strain exerted on the carriage. The object, then, to be attained is 
to exert a low maximum pressure throughout a long bore, in order to 
give the projectile a high muzzle energy with as little destructive 
effect as possible on the gun and carriage. The destructive effect 
on the carriage depends in a great measure on the maximum pressure 
in the gun, and will be less in proportion as a lower maximum pressure 
is obtained in the gun. It is not meant that the work done in recoil 
exerts no destructive effect on the carriage, but that for a given 
muzzle energy of the projectile this necessarily destructive effect may 
be very much modified by the employment of a comparatively slower- 
burning powder and a long bore.* 
The Committee on Explosives experimented on the original gun of 
12 ins., of 35 tons, by lengthening the bore 3 ft. On firing the same 
charge of powder, it was found that the additional length of bore 
“ yielded a gain in muzzle velocity of about 60 f.s., or nearly 5 per cent., 
on that obtained with the shorter gun.^f 
As the calibre is increased, the powder charge is burnt more profit- calibre, 
ably— i.e., more useful effect is obtained from the powder, and the 
muzzle velocity of the projectile is increased. The internal space for 
the expansion of the powder charge increases as the square of the 
* Vide example, p. 44, 
f Vide “ Beporfc on the Experimental Billed MX, Gun of 38 tons,” 
