Welcome! I'll start with the word police thing, you do not have an AR-10, AR-10 denotes an Armalite rifle, you have a 308AR, LR-308, DPMS pattern rifle. Seems trivial but when buying parts it can matter.
What brand receivers? How is the barrel fit in the upper, tight, loose? I assume the headspace checked out? Check the usual suspects, loose mounting of the optic, condition of the barrel crown. Inspect an unfired round, after it has been fed, for any damage to the bullet. I'm sure others will be along shortly with more questions or answers.