i never had a problem with mr ar15s. they were colt. worked flawlessly even with vietnam era magazines.. aluminium followers. $7 from numich arms.
the last 15 i had was stag arms. no carry handle and chambered for .223 instead of 5.56mm. no flash hider. worked ok. but it is hard to beat an early colt carbine in 5.56. i use to shoot rabbits with it unscoped. awesome little rifle