My Evil Black Rifle® is now more evil…it now takes detachable magazines. :) The fixed magazine will still fit, but it requires disassembly to switch back to it. I have 10- and 20-round detachables, so there’s not much reason to switch back. The detachables also provide an extra degree of 922(r) compliance, for what that’s worth (they replace three possibly foreign parts with three known domestic parts).