Mechanically fitted bullets are a very interesting side topic in the evolution of projectiles, a development of the family tree gradually died out. Created with studs, a belt or grooves, the bullet is muzzle loaded into the rifle with its projections engaging with the rifling from the moment it is loaded. With the aid of a ramrod, the bullet is pushed down to the breech, twisting through the rifling as it goes. On firing, it twists back up the barrel at great speed, without the necessity to expand as it already fully fills the grooves. The drawback to the system is that the bullet is a snug fit to the bore and after numerous shots the barrel is likely to become fouled with powder residue and the snug fitting bullet becomes very difficult to load. The British military had a small number of mechanically fitted projectiles in their service in the mid 19th century, starting with the two-groove brunswick and its belted-ball. Major (later Colonel) Jacob introduced his rifle and projectile with four studs into the Bombay Native Infantry of the East India Company India in the 1850s (it was not accepted in Britain) and the Whitworth rifle and its hexagonal bullet, probably the most famous of the mechanically fitted system of all, were introduced on a small scale into the British army from 1862. There were however, many commercially produced mechanically fitted projectiles, some of which were in use across Europe from the 1750s (see Schön’s Rifled Infantry Arms: A brief Description of the Modern System of Small Arms as adopted by the Various European Armies, 1855) , while in Britain, Purdey seems to have done an excellent job revitalising the mechanical fit concept, from the 1850s.
Mechanically fitted projectiles are designed for muzzle loading and I have yet to see a breech loaded mechanically fitted bullet. The reasoning behind this is that bullets loaded at the breach can be made slightly bigger than the bore and on firing, the bullet is pushed forwards and squeezed into the rifling. A mechanically fitting breech loaded bullet would be an over complication of manufacture.
The moulds of shot of this type were often made incorporating a small element sawn-off the end of the rifle barrel. John Norton, in 1830, describes this in the United Service Magazine, and Henry Wilkinson confirms this as the best method for attaining a good mechanical fit, in Engines of War, from 1841. The mould formed in this way will create a projectile which is a perfect reverse of the barrel and should therefore be a perfect fit. It will be noted that there is no windage in this method.
Mechanical fit projectiles
