You could put together an 18" SS barreled AR with a rifle-length gas system and a fixed A2 stock. There are some really nice 18" rifle length gas uppers out there. BCM makes some that I covet sooo much. A rifle length gas system should be a soft shooter, and even a mid weight profile would shoot very nice groups. BCM SS410 barreled uppers are known for shooting subMOA groups with the right trigger, optic, and ammo. They'll shoot both 5.56 and .223, they're well priced, and they're high quality.