Elswick Coned Interrupted Screw
Britain enthusiastically adopted the new quickfiring technology, using brass cartridge cases for all calibres up to 6 inches in the late 1880s and early 1890s. However, unlike Krupp and Hotchkiss, British-designed quickfiring ("QF" in British terminology, which became synonymous with charges in metal cartridge cases) continued to use screw breech blocks, but with their function merely to lock the cartridge in place rather than provide obturation. The powerful backward force generated by 6-inch QF guns still required a strongly-seated breech screw with as much thread as possible. However, a basic interrupted-thread screw sufficiently long enough to have enough thread to secure the cartridge on firing still required three separate motions to operate : rotate, withdraw, swing aside after firing, and repeated in reverse before firing. Elswick Ordnance Company (Armstrong's ordnance arm) developed a coned version of the interrupted-thread screw, with a decreasing rather than constant diameter towards the front. This eliminated the second "withdrawal" motion, with just two motions now necessary : rotate and swing aside. This proved short-lived, with Britain adopting charges in bags using the Welin stepped interrupted screw for all guns 5 inches and up within several years of it becoming available.
Read more about this topic: Rifled Breech Loader
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