I was trying to loosen the muzzle brake on my Steyr HS50 .50 BMG rifle once with a 12oz plastic hammer, I gave it a good smack and it spun and I thought great when I went to unscrew the brake the barrel unscrewed from the barrel bushing. I freaked out, I made a bushing for my barrel vice and bolted it to my mill table, a 2" opened end wrench fit over the barrel bushing with a index card shim and I torqued to about 200lbs, It has never moved since.
Casey