Ash
Member
Rifles aren't really designed to fire steel rounds per se. I think the real problem lies in the fact that steel is less elastic than brass. As a result, it may contract less after firing than brass does and so grip the walls of the chamber. In tapered rounds like 7.62x39 or 54r, the rounds eject easier because once you start movement, case-to-chamber friction is not a problem. The 5.56 round is straight-walled, which means it could grip the chamber and be harder to begin extraction, causing a jam. The US Military issued vast numbers of steel-cased 30 carbine, which is straight walled, to carbine manufactures for use in proof firing and testing m1 carbines. This ammo proved very satisfactory and is straight-walled, so there must also be design issues with the AR that make it less compatible than other designs.