Thx guys.... it’s in a magwell vise for those who asked. I’m just gonna slowly cut into it this weekend. Tired of messing with it.
Was heat applied to release the thread locker?
That was a crack that appeared after 150 rounds due to a stress fracture caused by an improperly installed receiver extension.
Ouch! Haven't seen that happen (yet). But I have seen two AR's from a local builder jettison the barrel when the front of the upper receiver failed. Builder stated doesn't use a torque wrench, he just "pulls them up tight". Every threaded fitting on the planet has a specified torque range for a very good reason!