Originally Posted by 3/325
Well let's take this a step further.
If you use the M16 bolt carrier, hammer, trigger, disconnector and selector as outlined in the ATF link previously posted the gun will fire more than one shot with each pull of the trigger (although it probably wouldn't be safe). This is assuming that the selector isn't on safe or fire but is moved past the fire position (which an M16 selector allows). This is because with the trigger held back it wouldn't be able to catch (unlike when an AR FCG is used) and would cause the hammer to keep going forward until the trigger was released (at least the way I understand it). Using a R.D.I.A.S. (Registered Drop In Auto Sear) would make for the safe use of those parts in an AR for full-auto and is legal. Not using a D.I.A.S. that is registered is obviously illegal. A R.D.I.A.S. doesn't need a hole drilled in the receiver for it to work. Or one could just buy an M-16.
Just using an M16 upper wouldn't be a problem - the problem comes when the other M-16 parts are installed in the lower. If someone is feeling anal they could use an AR bolt carrier in the M-16 upper and along with the AR parts in the lower there would be none of the parts listed in the link - hence no full auto. Why make it complicated?????