PRINCIPLES OE GUNNERY. 
61 
The muzzle velocity, under certain conditions,* is slightly increased 
by enlarging the powder-chamber; as the cartridge becomes shorter, 
and more space is allowed for the expansion of the powder charge. 
The charge is probably exploded more uniformly and rapidly in a 
chambered gun; but the disadvantages of too rapid an explosion may 
be modified by the use of a slow-burning powder, and also by allowing 
sufficient air space behind the projectile, by means of which the 
extreme pressure of the powder gas is relieved at the critical moment. 
By chambering the gun, a larger charge of powder may be profitably 
burnt, with this advantage—that a higher muzzle velocity is obtained 
with the same maximum pressure per square inch in the chamber, 
than with a smaller charge in an unchambered gun. 
Experiments with chambered guns have been carried out in the 
Royal Gun Factories, Woolwich, 1873, by Major Maitland, R.A. A 
10-in. M.L. gun was chambered to a diameter of 12 ins. for a length of 
19 ins. It was fired with a charge of 85 lbs. P., which gave a less 
maximum pressure than the unchambered gun with the service charge 
(70 lbs. P.), while the muzzle velocity was increased by 75 f.s.f 
But when large charges are rammed up tight, it is found that the 
pressure in the powder-chamber increases, as well as the muzzle velocity 
—the former sometimes to a dangerous extent. The object of the 
artillerist is to get the greatest amount of work out of a gun with safety, 
quite irrespective of the means employed. To obtain a high muzzle 
velocity with a low maximum pressure, it is necessary to maintain 
that pressure as much as possible while the projectile is moving along 
the bore. This may be done by increasing the ordinary charge of 
powder (when rammed up tight), and giving air-space , so as to allow 
for the expansion of the powder gas at the first instant of explosion; 
thus tending to keep the maximum pressure in the powder-chamber 
within safe limits. 
Air-space is usually given by lengthening the cartridge, and then 
ramming home the projectile, so as just to touch it; but the principle 
of the employment of an air-space depends on the ratio of the bulk of 
the charge to the number of cubic inches of space in rear of the 
projectile. It is usually measured by the number of cubic inches 
occupied by each pound of powder in the charge, when the projectile 
is in its proper position for firing. 
The amount of cubic space thus occupied by the cartridge has a very 
marked influence on the pressure in the gun and the muzzle velocity 
of the projectile. The effect of increasing the cubic space for a given 
charge of powder is to reduce both the muzzle velocity and also the 
maximum pressure in the powder-chamber; so that a much larger 
charge of powder may be fired with safety when a certain amount of 
air-space is allowed. This has led to the employment of much larger 
charges in the heaviest guns than were originally contemplated; the 
maximum pressure being still kept within safe limits, while a con¬ 
siderable increase in muzzle velocity has been obtained. 
* With small charges, chambering reduces velocity; with medium charges, slightly increases 
velocity; with large charges, greatly increase velocity; but in all cases reduces pressure, 
t Vide “ Treatise on the Construction and Manufacture of Ordnance in the British Service.” 
