I’ve seen some previous discussion about muzzle brakes and their respective diameters and thread pitches. My concern is how far can a barrel diameter safely be turned down? And how much shoulder depth is ideal for the brake to mate up with. Anyone out there with enough experience to know how much is too much? Is there a danger in turning a 30 cal barrel down to 1/2-28 for example? Going up to 9/16 = .5625 would leave an extra 30 thou of barrel thickness remaining. On a .600 barrel, that would leave roughly 40 thou total thickness, and a 20 thou shoulder. .300 bore minus .5625 leaves .262 total for a .131 barrel thickness. If you see where I’m going with the math, a .600 barrel turned down to .500 with a .300 bore would leave .200 total and a .100 barrel wall thickness remaining and a .050 shoulder. Again the question is “Is .100 enough barrel wall thickness to hold up to the pressure created by the brake?” And is a .050 shoulder enough to keep the brake in solid alignment with the bore? Who out there has done enough of these jobs to know where safety meets or exceeds function?
Not sure I can answer your question to your satisfaction but here goes. KDF makes several brakes in various diameters with a thread pitch of 1/2 x 28. They list their max caliber of 8mm or .32 caliber. So 1/2 x 28 thread pitch would be OK for your .30 caliber gun. As far as the shoulder is concerned it shouldn’t matter, there just needs to be something for the brake to screw up to so it gets tight on the barrel. There isn’t any pressure from the brake as the bullet exits the bore and the gases pushing it enter the brake and brake holes and pull the gun away from the shooter. No pressure but the brake is being pulled away from the gun/barrel. Ken
Answer
As per Ken’s numbers, I did a quick calculation:
Minor diameter of 1/2 x 28 thread ~ 0.5″ – 0.035″ = 0.464″
Groove diameter of 8mm bullet = 0.323″
Barrel wall thickness = 1/2 * (0.464 – 0.323) = 0.071″
The total steel cross-section area under the threads is less than 0.1 inch-square. Whether it is adequate depends on the design of the brake and the round being fired. Theoretically the braking force could be as much as the recoil. Apparently it is adequate for this particular brake. TL
