No! Using an M16 or full-auto BCG in any AR-15 is 100% legal. They are not regulated by any laws, whatsoever. SIONICS only uses full mass BCGs to ensure the most efficient cycling and consistent bolt speed.
The AR-15 bolt carrier group (AKA the BCG) is the part of the rifle or pistol that is responsible for performing semi-automatic fire when the trigger is pulled. It does this by first allowing the firing pin to strike the primer on the chambered round. Then grabs and ejects the spent shell casing from the fired round. It then re-cocks…