Page:Miscellaneous Papers on Mechanical Subjects.djvu/88

76 barrel internally, that is, with a mechanical fit, metals of all degrees of hardness, from lead, or lead and tin, up to hardened steel, may be employed, and slowly-igniting powder, like that of the service, may be used.

Having noticed the form of interior which provides the best rifling surfaces, the next thing to be considered is the turn, that is, the proper curve which the rifled barrels ought to possess in order to give the projectile the necessary degree of rotation; this, in all cases must be sufficient to keep the projectile with its point foremost.

The Enfield rifle, with one turn in 6 feet 6 inches, causes the bullet, on issuing from the muzzle, to rotate once on its axis in six and a-half feet. This moderate degree of rotation only admits of short projectiles being used, as long ones turn over on issuing from the barrel, and at long ranges, the short ones become unsteady.

With the hexagonal barrel, I use much quicker turns, and can fire projectiles of any required length, as with the quickest that may be desirable they do not "strip." I made a short barrel with one turn in the inch (simply to try the effect of an extreme velocity of rotation) and found that I could fire from it mechanically-fitting projectiles made of an alloy of lead and tin, and with a charge of 35 grains