You're not hurting a 1 1/16"-16 Class 3 thread at 150 ft-lbs, or even double or triple that value. It's not particularly easy to casually obtain a potentially harmful level of barrel torque, given the lack of tooling features to do so. You'll spin the barrel (which I remind you is round and thus tends to spin in the vise) or damage the receiver and/or receiver wrench well before the barrel threads are at risk of harm.
Since you want to apply your knowledge of automotive repair, please consider that the little lugs on my van are 14.5x1.5 mm (way smaller diameter and similar pitch to a standard R700 tenon), and carry a recommended torque of 165 ft-lb. They don't gall or break, despite dozens of torque cycles over their life. It's also not a torque value that will be casually exceeded by most men, although my dad was a diesel mechanic who thought that 150 ft-lb was a good spec for the pickle jar lid and maybe that's also the case for everyone else in this thread.
I understand that one of the requirements of maintaining the Loudmouth Asshole persona requires diligently weighing in on a nuanced discussion with overwhelming certainty that is based upon irrelevant experience. but this is one of those times where you could likely find easier pickings in a different conversation. Hint: find something that's subjective and non-technical, or at least one in which guys like
@kthomas haven't already contributed.
I mean, there are some ways to poke holes in my arguments, but that's not one of them. Steel-on-steel is about as common as it gets for bolted joints. 
