60 
PRINCIPLES OP GUNNERY. 
calibre, so that more work is done by tbe powder in tbe larger 
calibre; or, looking at it in another point of view, as tbe calibre 
increases so tbe base of tbe projectile is enlarged, and tbns a greater 
surface is exposed to tbe action of tbe powder, and consequently tbe 
projectile is pushed forward with a greater aggregate pressure, and 
hence a higher muzzle velocity for a given length of bore results. 
But there are other considerations which limit the calibre of guns. 
For when the calibre of the gun is increased, 
(1) The total rending force, tending to burst the gun, increases 
(supposing the internal pressure per square inch the same) 
as the calibre. 
(2) The resistance of the air to the motion of the projectile in¬ 
creases, and with projectiles of similar weight the velocity 
is lost more rapidly. 
The first consideration operates most powerfully in the heaviest 
guns; the second in field and siege guns for direct fire. 
In experiments with the 38-ton gun, the 12'5-in. calibre imparted a 
higher muzzle velocity to similar projectiles, when fired with equal 
charges, than the 12-in. calibre—which was one of the reasons why 
the 12'5-in. calibre was eventually adopted. 
With field guns, on the contrary, the result of experiments has been 
such as to justify a diminution of calibre for the same weight of 
projectile; since the remaining velocity, at ordinary artillery ranges, 
has an important practical effect on the precision and decision of fire. 
In order to test the effect of the variation of the calibre of a gun, 
when firing the same weight of projectile with the same charge, both 
as regards muzzle velocity and remaining velocity, at a given range, 
experiments have been made with the polygroove M.L. 12-pr. gun to 
determine the remaining velocity of the projectile at 1040 yds. from 
the muzzle, by means of Le Boulenge's chronograph, with the fol¬ 
lowing results:— 
Table showing the Result of varying the Calibre of Field Guns . 
Weight of 
projectile. 
Weight of 
charge. 
Calibre of 
gun. 
Muzzle 
velocity. 
Remaining 
velocity at 
1040 yds. 
Loss of 
velocity. 
lbs. 
lbs. 
ins. 
f.s. 
f.s. 
f.s. 
12 
3 
3-0 
1690 
1208 
482 
12 
3 
3-2 
1718 
1144 
674 
This shows that although the muzzle velocity is slightly greater 
with the larger (3'2-in.) calibre, yet the remaining velocity at 
1040 yds. is considerably greater with the smaller (3'0-in.) calibre. 
Diameter In the more recently constructed M.L. guns the diameter of the 
powder-chamber has been made larger than the diameter of the bore 
space oecu-(or the calibre of the gun); partly to obviate the disadvantage above 
chlrg 1 ? 1116 alluded to, of increasing the diameter of the projectile, and partly to 
obtain a higher muzzle velocity, with more uniform results, 
