Rotation of ammunition

In 1855 Andrew Hotchkiss patented an RML projectile, in which two parts squeezed a lead ring to obturate the barrel under the pressure of gunpowder fumes.

Later the rotation was effected by a cupped copper disc called an "automatic gas-check" attached to the base end of the projectile.

A more regular and efficient action of the powder gas was thus ensured, with a corresponding greater range and an improvement in accuracy.

[1] Vavasseur devised the plan of fitting by hydraulic pressure a copper "driving band" into a groove cut around the body of the projectile and patented it in 1866.

[citation needed] It not only fulfills the purpose of rotating the projectile, but renders possible the use of large charges of slow-burning explosive.