Brownells 6.5 Grendel BCG...????

[VASCAR2]

As long as you know Brownell’s uses a shorter bolt and requires a shorter firing pin I think you can safely test the BCG. If the firing pin protrusion is on the edge of being in spec you might not experience any issue but I wouldn’t use standard small rifle primers with thinner cups. I use CCI 450 or CCI 41 primers (thicker primer cups) in my AR-15’s just to be on the safe side.

I have three Monster bolts IIRC and they are very good bolts. I’d have no hesitation using the Brownell’s bolt carrier and a Monster bolt with milspec firing pin.