Page:Miscellaneous Papers on Mechanical Subjects.djvu/96

 each side on which the projectile bears as it enters, proper windage is allowed,—the other halves of the sides are left to preserve a full extent of bearing surface as it comes out, and at the same time maintain its concentricity with the bore. This plan of providing for windage obviates the great evils which arise from eccentricity in the case of spherical shot.

The effect of a proper rifling turn, which varies according to the bore and length of the piece, produces, as has been before shewn, no loss of elevation while the rotation given to the shot adds greatly to its destructive power. The practice obtained from an ordinary 9-pounder brass field gun, rifled by me, proves that, with a charge of powder one-third less than the service charge, the range was one-half greater than that of the same gun with spherical shot.

In comparing the strain upon a rifled cannon with that upon a smooth bore, the work done by the respective pieces must be taken into consideration. If the full powers of the former are to be exerted, and, if the extreme ranges