Combine with an m16a2 burst trigger, M16 disconnector, FA selector, and 2 disconnector springs for selectable safe, fire, binary. After firing the first round in binary mode you can move the selector back to fire while holding the trigger down to cancel the second shot. I got the idea for the selectable binary from @UberPoor:9 and the general binary disconnector mechanism inspiration from @pembie000industries:1 I just worked out the angles to make it cancellable. I have only tested in PA612CF. STL, STEP, and DXF are included so knock yourself out.