Not sure where or who told you that, but it is wrong. Per the Technical Manual;
Torque barrel nut assembly (19) again to 30 ft-lb (40.5 N-m) while maintaining sight alignment. Barrel
nut assembly may be tightened beyond 30 ft-lb (40.5 N-m) to align barrel nut assembly serrations for
proper gas tube clearance. Never loosen barrel nut assembly to align for gas tube clearance.

