54 
PRINCIPLES OP GUNNERY. 
CHAPTER IV. 
Work Done by a Charge op Powder in connection with Muzzle 
Velocity and Pressure in the Bore. 
Work done by Powder.—The Velocity of a Projectile at any point in the Bore of a Gun.—Muzzle 
Velocity.—Approximation to the Muzzle Velocity of a Gun by means of Noble’s Tables.— 
Circumstances affecting Muzzle Velocity.—Charge of Powder.—Nature of Powder.—Weight 
of Projectile.—Length of Bore.—Calibre.—Diameter of Chamber, and Cubic Space occupied 
by the Charge.—Windage.—Position of the Vent.—Twist of Rifling. 
by°powder e Comparatively little was known of tlie work done by the explosion 
of gunpowder until it was made the subject of enquiry by Captain 
A. Noble, late R.A., F.R.S., and Professor Abel, F.R.S. Their re¬ 
searches have thrown much light on the subject. The results of 
their experiments are expressed by connecting the number of volumes 
of expansion of the powder charge in the bore of the gun with the 
maximum work per pound of powder which the powder is capable of 
realising. 
The amount of work capable of being done on a projectile by the 
charge of powder in a gun depends principally upon the ratio of the 
cubic space occupied by the charge to the cubic capacity of the bore 
of the gun. This is modified in practice— 
(1) By the nature of the powder—its density, hardness, &c., and 
the size and shape of its grains. 
(2) The method of ignition adopted, and the position of the vent. 
(3) The amount of air-space allowed. ( Vide p. 61.) 
(4) The weight of the projectile, its resistance to motion (both 
of translation and rotation), frictional and other resistances 
—whether due to compression (as in the Armstrong B.L. 
system), or to expansion (as in the poly groove M.L. 
system), or to the gas-checks used with Woolwich guns. 
(5) The quantity of heat absorbed by the gun. 
The annexed table is taken from the results obtained by Noble 
and Abel. The curve deduced from their experiments is given in 
Plate II. 
A pound of powder is taken to occupy a space of 27*7 cub. ins. 
The number of volumes of expansion of the powder charge in the 
bore of a gun is obtained by dividing the cubic capacity of the bore of 
the gun by the cubic space actually occupied by the charge under the 
above conditions. 
