180 
MINUTES OF PEOCEEDINGS OF 
THE DERIVATION* 0E ELONGATED PROJECTILES 
FIRED FROM 
RIFLED ORDNANCE. 
BY MAJOR C. H. OWEN, R.A. 
PROFESSOR OF ARTILLERY, ROYAL MILITARY ACADEMY. 
Although accuracy of fire has been greatly increased by the introduction 
of rifled guns, the projectiles fired from them are as liable to deflection by 
wind as the balls thrown from smooth-bored pieces ; but besides this deflec¬ 
tion, it is found that the elongated shot fired from rifled guns are subject 
to a constant deflection to one side or the other, according to the direction 
of the rotation given to them by the gun and the form of the head of the 
shot ; this constant deviation which has been termed by the French, derivation, 
would occur in a perfectly still atmosphere. 
Nearly all the different rifled guns, either ordnance or small arms, that 
have been made give their projectiles what is called a right-handed rotation, 
i.e. the upper part of the shot turns from left to right with reference to 
an observer behind the gun; and it has been found, that when, as is 
generally the case, the projectile has a rounded or pointed headt, it invari¬ 
ably deflects to the right.% 
On the contrary, projectiles- having round or pointed heads fired from the 
few guns that have been rifled so as to give a left-handed rotation, (i.e. the 
upper part turning from right to left with reference to an observer behind 
the gun), deflect to the left. The amount of this deflection or derivation 
is influenced chiefly by the form of the head of the shot, the initial velocity 
of the shot on leaving the bore, the velocity of rotation given to the projectile, 
and the force and direction of the wind. 
Table I. shows the deviations to the right of shot fired from a 40-pr. 
Armstrong gun which gives a right-handed rotation; in Table II. may be 
seen the left deflections of shot fired from a gun rifled according to a French 
system, and giving a left-handed rotation. Both the Armstrong and French 
projectiles are cylindro-conoidal in form. 
* It has been suggested that the term deviation would be better understood than derivation. 
The word deviation could not however be used without adding constant before it and due to rotation , 
&c; after it, or the peculiar deflection called derivation would be often confused with that due to 
wind or other causes. I may add that the term has been in general use for some years in England, 
America, and on the Continent. 
+ Either hemispherical, conoidal, conical, or ogival. 
J It is to allow for the constant right deflection or derivation of the projectiles fired from the 
service rifled ordnance, that the tangent scales are now made to slope to the left. 
