PRINCIPLES OF GUNNERY. 
CHAPTER II. 
Terms , used in G-unneey. 
( Continued .) 
Rifling.—Angle of Spiral.—Twist of Rifling.—Relation between Angle of Spiral and Twist of 
Rifling.—Determination of the Twist of Rifling at any point in the Bore.—Determination of 
Linear flotation of the Exterior of the Projectile, while passing down the Bore.—Examination 
of recovered Projectiles for groove-marks on Body and Studs.—The Motion of Translation and 
Rotation of a Projectile fired from Rifled Ordnance.—Velocity of Translation.—Velocity of 
Rotation.—Linear Velocity of Rotation.— Work.—Pressure per square inch on the Bore of 
the Gun.—Work Done per square inch.—Energy.—Energy per inch of Circumference.— 
Energy due to Translation,—Energy due to Rotation.—Total Energy.—Pressure required 
to give Rotation to Projectiles.—Velocity of Recoil.—Gun Pendulum.—Experiments on 
Recoil.—Energy of Recoil.—-How the Energy of Recoil may be Reduced.—Kemmis’s Table 
of Service M.L.R. Ordnance. 
All rifled guns have grooves cut spirally in the bore, in order to Rifling, 
give the projectile rotation round its longer axis. 
The angle of spiral (or angle of rifling) differs in different guns, of 
depending principally on the length, weight, and muzzle velocities of 
the projectiles fired from them. 
It is measured at any point of the groove, in guns rifled with 
increasing twist by the angle which a tangent to the groove at that 
point makes with a line in the bore parallel to its axis; and in guns 
rifled with uniform twist , by the angle which the groove itself makes 
with a line in the bore parallel to its axis. 
Suppose AB to represent the length of the rifled part of the bore of 
a gun rifled with increasing twist, AC the groove with increasing twist, 
AB the direction of the axis of the bore —A at the breech end, B at the 
muzzle. 
Then the angle of spiral at the point P' of the groove (corresponding 
to P in the axis of the bore) is measured by the angle P r TB, where 
P'T is a tangent to the curve at the point P'. In guns rifled with 
increasing twist, the angle of spiral at the muzzle is called the final 
angle of rifling and that at the breech end of the rifling is called the 
initial angle of rifling. PP 1 and BC represent the linear distances 
through which the exterior of the projectile has rotated when it has 
arrived at the points P and B in the axis of the bore respectively. 
The twist of rifling, with uniform twist, is estimated by the distance Twist of 
(generally expressed in calibres) in which the spiral makes one turn ; 
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