This SA-G12 AR36 was returned to us due to an issue with semi-auto. Having fully tested this AEG I can confirm that having put over 50 rounds through it in semi-auto, I found no issues. The mock bolt, however, will not return fully and stays about 5mm from closed. This doesn't affect any functions of the replica, even the electric blowback, which still cycles the bolt and feels and sounds great. If you can't live with it you can disable the blowback, which will allow the bolt to close, but it will no longer cycle as the AEG fires.