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

by Ernest Christian Wilford

As accuracy of direction is the result of a spiral motion round an axis coincident with the flight of the bullet, communicated to it by the grooves, it is clear that the depth, number, and form of the grooves should be such as will hold the bullet firmly, and prevent all tendency to strip.

On the degree of spirality.

The degree of spirality should be sufficient to retain the projectile point foremost during the whole of its flight. It was at one time supposed that if the spiral turn was great, and the charge strong, the bullet would not conform, but strip, and that the same results would occur even with grooves but little curved. Unquestionably this would prove true if certain limits were to be exceeded. A false conclusion was built upon this theory, viz., that the greater the spiral turn the less the charge should be; and that therefore in rifles intended for war, the greatest initial velocity being required to produce the greatest range, the groove should have as little turn as possible; for extreme ranges have been obtained with Jacob’s, Whitworth’s, and Lancaster’s rifles; the first has a full turn in 24in. the second in 20in. Sharp twist and large charge not cause stripping.These rifles perform well with 90 grains of powder, and both Whitworth’s and Lancaster’s might even fire better were the charge of powder increased to 100 grains, the recoil might be objectionable while there would be no symptoms of stripping.

On depth of groove.

Great depth of groove can only be hurtful, owing to the difficulty of closing up all passage to the gas, which should not be allowed to escape round the bullet, as this would cause deviation and shorten range. Deep grooves become a receptacle for fouling, are difficult to clean; and high projections must offer great resistance to the atmosphere, and particularly to a side wind.

Patches.

When fustian or leather are used as patches, they receive and communicate the spiral motion to the bullet, without the zone of the projectile being at all indented, but in this case the spiral must be diminished, otherwise the bullet would not turn with the grooves. If the patches be made of a thick material, the grooves should be many, broad, and not too shallow, in order to receive the folds of the patch.

Shallow grooves best.

From our present amount of experience it seems safe to conclude that the shallower the grooves are the better, so that they perform their intended functions.

Proportion of groove to land.