RIFLE, or RIFLED, is a term applied to muskets or pieces of. ordnance when their bores are furrowed with spiral grooves ; the grooves or channels being formed by a machine which scrapes away the substance of the barrel interiorly in parallel and serpentine directions.
The object to be attained by this grooving may be thus explained. A bullet made of lead cast in a spherical form, according to the practice till lately followed, having unavoidably some irregularities on its surface, and fre quently, from unequal expansion, a cavity in the interior ; it follows that, when such bullet is discharged from a common musket, it devi ates continually from the direction which it should take by gravity and the impulse of the fired gunpowder. The intention therefore in forming spiral grooves within the barrel of a musket or piece of ordnance, is, to produce a rotatory motion of the shot about an axis which shall coincide with the line of its path, in order that the unequal pressure of the atmos phere in its front, on account of any irregula rity in its form or density, may correct at every half-revolution of the shot on such axis. The number of spiral channels in a rifle-musket is, in general, two ; and one revolution of the spiral, in the whole length of the barrel (=30 inches) is considered sufficient.
The most general practice of late has been to press the bullets (by means of the ramrod) into the barrel upon a piece of greased cloth or leather (called the plaster). But, at present, rifle-bullets are made with a projecting zone which surrounds them on the circumference of what may be called a great circle. The pieces are loaded at the muzzle, and the parts of the zone which are diametrically opposite to one another are those which pass along the two grooves in the barrel.
Bullets for common muskets, as well as for rifle-barrels, are not now cast in their actual forms, but are made from lead which has been previously cast in cylindrical rods. The bullets are then formed by compressing the rods between two revolving cylinders. The pressure, by forcing the particles together, fills up any vacuities which may form them selves in the rods during the cooling process, and probably renders the density of the hall nearly uniform. Bullets and balls have occa sionally been made of other than a spherical form, as experimental means of determining the best form for ensuring a direct course.