382 
MINUTES OF PROCEEDINGS OF 
The bad shooting of the original Lancaster gun is an illustration 
of the effects of want of centring. The outrageous system of rifling, 
together with the badly fitting projectile which was adopted in this gun 
originally, made it an impossibility for the shot to come out properly 
centred. The consequence was that the practice made by it was most 
erratic, even with very high velocities, and the very considerable 
rotation which was given. The path of the projectile could be traced 
by the eye as it described a sort of spiral, sinuous, or corkscrew 
motion, at one time deflecting to the right, at another to the left, and 
so on. Yery much better shooting has been obtained from guns with 
one-third of the twist, and there can be no doubt that the reason is to 
be found in the fact that they delivered their projectiles better centred. 
It is a curious fact that, with our service projectiles, the deflection is 
always to the right; and to this, no doubt, is due the accuracy of fire 
which is obtained with them; for if at one time they should deflect to 
the right, and at another to the left, it would hardly be possible to 
make accurate practice. A very crude theory, which has found con¬ 
siderable acceptance, has arisen from this fact. It is that “a shot 
rotating rapidly, and at the same time falling in the air, will ex¬ 
perience a greater pressure underneath than above, and will therefore 
roll, as it were, on the denser air below.” That this cannot be the 
case is at once evident, when we remember that, according to the 
principles determined by Bobins and Magnus in the case of round 
shot, it ought to produce a deflection in exactly the opposite direction; 
and, if it were the true reason, our service rifled shot ought to deflect 
to the left instead of to the right. 
Professor Bashforth offers a better explanation in his valuable book 
on the “ Motion of Projectiles,” recently published. He says (p. 65) :— 
“ The shot will have a sinuous motion. But as the first deflection of 
an ogival-headed shot spinning with right-handed rotation is to the 
right, and afterwards, as its point is directed more to the right than 
to the left, the shot will have a deviation on the whole greater to the 
right than to the left.” 
By plotting some very accurate practice made with a B.L. 40-pr. 
Armstrong gun—* which is perhaps the most accurate shooting gun we 
have ever had in the service—it will be seen how the deflections vary. 
There is little or no deflection up to 700 or 800 yds. Then the deflection 
begins to be appreciable, and increases up to about 1200 yds., when 
the rate of deflection appears to attain a maximum. After that, the 
rate of deflection to the right decreases, but no deflection in the 
opposite direction to the left can be traced. Prom about 1500 to 
2000 yds., or more, there appears to be very little tendency to deflect 
at all; but beyond that, the deflection to the right begins again to 
manifest itself, and at about 2500 yds. range it has again attained a 
maximum to the right, gradually after that diminishing, and, at more 
than 3000 yds., showing some symptoms of deflection to the left. 
The following diagram will very well represent the deflection of the 
* “Proceedings O.S.C.,” 22nd October, 1862, Minute 7634. 
