I need a new vise block for this exact reason. Do you recommend the Magpul one? I broke my last upper block and haven’t replaced it yet. Still have an AR torn apart needing to get put back together.
Smacking the wrench with the long pipe will get it loose quicker than just tugging on it. The jolt of being smacked will knock it loose.
I would have tried heat first. If you could have heated just the nut and not risk damage to the receiver.