Almost every description of twist, number, &c., &c., of grooves have been tried, according to the individual tastes and theories of the manufacturers. It is absolutely necessary to have two grooves, as a single one would give a wrong direction. Rifles have been made with, from two to one hundred and thirty three grooves, and in the majority of cases, an odd seems to have been preferred to an even number. In Dean’s Manual it is stated, Degree of spirality.that “in the numerous collections of arms that have at various times come under our personal notice, some were rifled with straight, but the majority with grooves in a spiral line, sometimes with a half, sometimes a three quarter, and seldom more than a whole turn in a length of two, two and a half and three feet; deviations based upon no principle transmitted to us, but requiring nevertheless a decided research for principles upon which to establish a theory; we have also met with every one of those configurations of the spiral and form of groove, &c., &c., which have been arrogated as modern conceits and discoveries.”
Spirality.
Some rifles have sharp muzzle twist decreasing to the breech;—sharp breech twist decreasing to the muzzle; an increase of twist in the middle of the barrel decreasing at both extremities.
Modification in France. 1740.
In France a modification of the Carabine took place in 1740;—the grooves were made to begin at eight inches from the muzzle, the unrifled part being of the same calibre as the bottom of the grooves, so that the bullet might pass easily; thus also facilitating the loading of the weapon.
Rifled only at muzzle.
There is an old rifle in the United Service Institution, and also a barrel brought from Lucknow, (in the Model Room of the School of Musketry,) grooved only for about one foot from the muzzle, the remainder of the barrels are smooth bored.
Degree of spirality.
The degree of spirality is found to vary from a whole turn in 1 foot 5-in., to a whole turn in 11 feet.
Depth of spiral.