Re: barrel diameters and muzzle brakes.
I've been concerned about min thread diameters especially with factory RUM's which seems to be the most popular to brake if you can imagine that.
I talking it over with an engineer who is familiar with what I'm doing and he put together a program for me to just punch in numbers and it tells me where I'm at and gives me a safety factor for that specific case since it changes with bore diameter. He built in some safety by using the numbers for 416 Stainless in an annealed state.
I punched in the a .310 bore with .648 OD and my program tells me it's good to 18,000 psi muzzle pressure with annealed 416, a bare 9/16-28 thread is right at the line with annealed 416, I forget the term he used but that line is just where the metal will start to move but it will spring back and not permanently deform or fail for quite a little more pressure so a 9/16-28 is well within spec and 1/2-28 is good for 13,000 psi on annealed 416. A 4140 barrel steel is good for quite a little more and a 1/2-28 is well within it's operating range on the .310 bore.
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