361 
PRINCIPLES OF GUNNERY. 
RIFLED ORDNANCE. 
BY 
CAPTAIN J. SLADEN, R.A. 
EROEESSOR OE ARTILLERY, R.M. ACADEMY, WOOLWICH. 
{Continued from p. 284.) 
CHAPTER VII. 
Drift of Elongated Projectiles. 
Rotation round the Longer Axis of a Projectile.—Method of giving Rotation in Service Ordnance. 
—Circumstances which Determine the Velocity of Rotation required to keep a Projectile 
Steady in Plight.—Effect of Non-Centring.—Effect of the Resistance of the Air.—Position of 
the Centre of Gravity.—Length of the Projectile.—Distribution of the Mass of the Projectile. 
—The Spiral Motion of an Elongated Projectile.—Illustrated by means of a Gyroscope.—• 
Drift of an Ogival-Headed Projectile.—Drift of a Plat-Headed Projectile.—Varying Con¬ 
ditions which affect the Drift.—Practical Conclusions. 
It lias already been stated (Cbap. I. p. 26) that sufficient rotation Rotation 
is usually given to an elongated projectile round its longer axis to fongeraxis 
keep it as nearly as possible point first, or, in other words, in the ^re¬ 
direction of the tangent to the trajectory, during flight. 
It is well known that if a service elongated projectile were fired with 
no rotation round its longer axis, it would oscillate about its shorter 
axis through the centre of gravity, and tend to set its longer axis at 
right angles to the direction of motion. 
Rotation is given in service ordnance in three ways Method of 
giving ro- 
(1) By means of a soft metal coating on the cylindrical surface of sSv°i?e a 
the projectile (slightly larger than the diameter of the bore) being orduance * 
forced into the spiral grooves of the bore j as in the Armstrong B.L. 
guns. 
(2) By means of studs on the projectiles fitting the spiral grooves 
of the bore; as in the French and Woolwich systems of rifling. 
(3) By means of a metal disc attached to the base of the projectile, 
and expanded into the spiral grooves of the bore by the impulse on 
firing; as in the more recent ordnance with polygroove rifling. 
The velocity of rotation required to keep a projectile steady in flight Circum. 
depends— which aes 
(1) On the centring, or otherwise, of the projectile as it leaves the the vei<> 
bore. tation re- 
, quired to 
(2) On the effect of the resistance of the air which the projectile k ^p ^ ile 
meets with, tending to give it rotation round its shorter axis. Steady In 
47 
flight; 
