Reuppered 14.5 Bushmaster in a deltonics flat top upper. Bought slightly used from a friend when it had an A2 upper on it.
Believed it locked back before new upper.
Previous range visit. Failure to lock back with all ammo tried.
Bolt carrier was a little tight. Bolt carrier now rides smoothly.
Return range visit. Will lock back every time on UMC yellow box but not on Win 223usa white box. Not this is not Q3131 or 3131A.
Carrier key appears tight, no visible leakage. Some slight leakage noted on handguard heat sheild at sight base.
Should I apply some sealant or loctite to gastube in sight base?
Will it lock back manually on an empty mag?
What stock are you using? If A1 stock are you using an A2 screw?
Whats the end of the gas tube look like? Any wear or deformation causing it not to seal well?
Good gas rings?
Mag catch adjusted correctly?
Is the gas key dirty? How about the bolt and carrier?
I'm gonna try swapping bolt carriers next. I do notice that the bolt is tighter in the gas ring area than the other bolt carrier I compared it with. Maybe it's too tight?