I have a 10.5 inch AR Pistol in 300 blackout that I built from an 80% lower kit purchased from Thunder Tactical. I was unsure of the company but very pleased by the fit and finish of what I got considering the ~$340 price. But, I can't get this thing to run subs, and that's the whole reason I bought it. This is my first AR so I figured I'd check if there's something I'm not thinking of that might me causing this
The details
10.5 barrel (bear creek)
pistol length gas
standard carbine buffer spring/weight
I'm only interested in finding a hand load to work with this, though I did try a box of Rem subsonics to make sure it wasn't just my reloading skills causing the issue. Without a can the bolt barely moves, with the can they eject but no lock back and tend to jam if more than one round is in the mag.
15gr RL7 + 180gr sierra PH cycles fine, and accurate but dirty. Sub sonic charge is about 10.5 and ejects but not enough to pick up next round. I've tried 3 different cast boolits from 200-220gr and ~10.5 RL 7 with the same results.
Seems the gun is short stroking. I've check the gas block alignment, cleaned the chamber, stripped and lubed the BCG, gas key is tight, tube is clear, gas rings are good. There's a bit of leakage around the gas block but it doesn't seem like enough to cause this. If anything the gun ought to be over gassed.
Is it possible that the RL 7 is too slow a powder? I'm wondering if maybe the bolt is unlocking too soon? The only other thing I could think of is that the gun IS over gassed and the mag can't catch up. Adjustable gas block on the way whenever I can find a SA block in stock.
Thoughts? Is there something I'm not thinking of that could be robbing the BCG of energy?