THE ROYAL ARTILLERY INSTITUTION. 
393 
however, has been inserted in each longitudinal row, which materially 
increases the strength. The studs are often very much worn by the 
great friction, which must necessarily cause a greater waste of longi¬ 
tudinal pressure than if so much wear did not take place, as well as 
try severely the driving edge of the grooves. 
Nothing has been said on the relative merits as regards centring of 
these systems of rifling, because little is known. The best way of 
testing them on this point would be to fire through a number of paper 
screens at different distances, so as to trace the trajectory, using at the 
same time the Bashforth chronograph to obtain the resistance of the 
air. The latter would give the amount of deflection of the point of 
the projectile, and the former the direction of the deflection. 
These considerations would appear to show that the palm of undoubted 
superiority cannot be given to any one system over all the others; each 
has its advantages and its disadvantages, and none are without objec¬ 
tions. This is generally admitted, and has come to be thought 
unavoidable in all rifling. That such, however, is not necessarily the 
case, is a consideration which the following proposal is intended to 
show. 
It may be briefly stated thus :—Adopt the system of grooving in the 
Austrian B.L. experimental gun, but do not adopt the lead-coated pro¬ 
jectiles. The lead-coated projectiles, in addition to the disadvantages 
pointed out, have the serious disadvantage mentioned by Colonel 
Beilly, R.A.,* of being less effective against armour plates than iron 
projectiles, because the lead flies off on impact and does not help the 
projectile through the target. But if we groove the projectiles so as 
to fit the projecting ribs of the gun, we do away with this objection, 
and we get an amount of bearing surface which alone meets the 
mechanical requirements of the case. With 64 grooves in the shot, and 
the same number of lands in the gun, each *3 in. deep, we have an 
amount of bearing surface which, under ordinary pressures, in a 15-in. 
gun, with a projectile of 1200 lbs., and a twist of one turn in 40 
calibres, would reduce the pressure below 700 lbs.f per square inch—the 
mechanical limit of pressure between surfaces in contact under friction. 
Here, then, is a perfect system of giving rotation. Tt does not cut into 
the bore of the gun, and therefore does not weaken it; and it will not 
wear the grooves, nor waste more than probably one-half of a per cent, 
of the longitudinal pressure of the gas, because with the small amount 
* “ Notes of a visit to Berlin, December, 1872,” by Lieutenant-Colonel E. Reilly, C.B., Assistant 
Director of Artillery, page 20:—“This lead covering causes a great waste of power, as it is the iron 
part alone of the shell that can do work against the iron plates, and consequently a considerable 
force is expended in projecting a part of the projectile which is useless for the work which has to be 
performed.” On this point Mr. Krupp remarks (letter 16th February, 1870), that the experiments 
at Tegel, 4tli August, 1868, “again demonstrate that, in the case of the breech-loading projectiles, 
a heavy lead-coating can so weaken the effect as to render it insufficient.” And Captain von 
Doppelmair—a strong advocate of Mr. Krupp—says: “We shall not be much in error when calcu¬ 
lating the momentum of a lead-coated shot if we only take into account the weights of the cast- 
iron or steel core” (pamphlet). 
f This is for ordinary pressures. With exceptional pressures, the same as in the other calcula¬ 
tions, the maximum would be about one ton per square inch. 
48 
