Class Book for the School of Musketry, Hythe / Prepared for the Use of Officers

by Ernest Christian Wilford

It is now generally recommended that the grooves be made broader than the lands, i.e., that the rifling surface should predominate over the unrifled part of the bore. Shallow grooves with rounded edges, have the advantage of not leaving any angular traces on the surface of the bullet, besides they afford a greater facility for cleaning.

Circular grooving.

Circular grooving is composed of segments of circles, leaving no sharp edges on the bullet, and is no doubt a very good form.

Gaining twist.

An American gentleman named Chapman, who has written a very clever book upon the rifle, is a strong advocate for the “gaining twist,” which form prevails generally in American rifles. He states, “In a rifled barrel, it is obvious that a bullet instantaneously started from a state of rest, with a velocity of 5,000ft. a second, must exert at the moment of starting, a tendency to move along the bore in a straight line. Cause of canting.However, meeting with the resistance that the lands employ to keep it to the twist, it communicates to the rifle itself a certain amount of motion in the direction of the twist of the creases, and this as the angle of the twist increases, combined with the size of the calibre, and the weight of the ball.”

Remedy for canting.

“If the angle of the twist at the breech end can be reduced, the bullet at the same time leaving the muzzle with sufficient spin to last throughout its flight, it is certain we shall have less twisting of the rifle in the marksman’s hands, less friction of the bullet against the lands, less tendency for the bullet to upset, (or be destroyed,) and consequently, from obtaining a higher velocity, (because enabled to use a greater quantity of powder,) less time for the action of regular or irregular currents of air.”

Uniform spiral by American Government.

After careful experiments by the American Government, preparatory to the establishing the model for their Military Rifle, it was decided that the turn for the grooves should be uniform; and that those with an increasing twist did not give any superiority of accuracy. The “gaining twist,” although adopted by Mr. Lancaster, is opposed by Mr. Whitworth, and all other Rifle manufacturers, and our increased experience does not prove it to possess any advantages over uniform spirality. Theory would indicate that it must occasion increased friction.

Decreasing spiral.