Rikta wrote:so given that only expanding gas comes in contact with the brake what is there really, aside from insane amounts of recoil on some massive magnums or wildcat rounds, that can break the brake?
The gas pressure is what will be relevant. These are rough numbers, but will give you an idea...
Peak chamber pressure from a .308 with a typical 165gr load will be somewhere in the neighbourhood of 58,000 psi.
Obviously as the bullet moves through the barrel, creating an increasing volume of space behind it, the pressure reduces. A quick bit of research would suggest that just before the bullet exits there muzzle of a 24" barrel you're looking at about 8,000 psi of contained pressure.
This would drop sharply once the bullet was moving away freely and no longer being restricted by the rifling but you're still talking about a significant amount of pressure being channelled through the first baffle of the brake. I dunno... maybe a split second peak of 5,000 psi? Honestly though that's a very rough guess and I could be wrong, it could be a lot lower.
Obviously it's manageable, as demonstrated by the fact there are a million people out there happily using brakes. Make a well designed brake using suitably strong material and it's fine.
If some knockoff merchant loosely copies a product they don't understand and has some fabrication place whip it up on the cheap using ??? metal, then who knows. I'm not saying this is the case for anyone in particular, but that would be the concern.