Rifled Breech Loader - Armstrong Screw Breech

Armstrong Screw Breech

Armstrong introduced improved designs in the 1850s and 1860s ("Armstrong guns" with his "Armstrong screw" breech) which involved loading the shell and gunpowder propellant charge (in a cloth bag) through the hollow breech screw, lowering a heavy block into a slot behind the powder chamber and screwing the breech screw tightly against the block to lock it in place. A degree of obturation was achieved via a cup on the face of the block being forced into a recessed ring on the chamber face. The system was in effect a vertical sliding block such as later used by Krupp in both horizontal and vertical form, with the crucial difference that Armstrong failed to make the progression to loading the powder charge in a metal cartridge, with the result that complete obturation was impossible : whatever obturation that was achieved relied on manual labour rather than the power of the gun's firing, and was hence both uncertain, based on an unsound principle and unsuited to large guns. Armstrong screw-breech guns were initially adopted by the British Army and Royal Navy, but concerns about limited armour penetration of the shells due to limited maximum velocity, safety concerns with the breech blocks blowing out of guns, and higher skill levels demanded of gunners led the British Government to revert to rifled muzzle-loaders from 1865 to 1880, when Britain finally deployed reliable screw breech mechanisms.

The Imperial Japanese Army used Armstrong cannon during the Boshin War to devastate the Aizu castle town and force its inhabitants to surrender quickly, and British Armstrong light field guns proved deadly against Chinese forces in the Second Opium War. However, the British Army and Navy preferred to revert to muzzle-loaders until larger high-powered breech-loaders with secure obturation systems that were relatively simple to operate were developed.