Gunsmithing Muzzle Brake

Try using the crush washer. Do not go over 35 ft/lbs. If you don’t have a torque wrench it’s worth buying one or an autozone will loan one to you.

Shim kit is probably worth the $10. Either way, I would use a few drops of either red locktite or rocksett for good measure.
 
With the suppressor off, it looks terrible.

I tried some aluminum black hoping it would work to no avail. I’ll throw on a little high temp spray paint and hope it doesn’t bubble off
 
Most shims are made from stainless steel, products like Perma Blue and Aluma Black won't work. I use shims quite a bit for my muzzle devices and I generally don't worry about the aesthetics of a thin sliver of stainless up at the muzzle. They're inexpensive, they do the job, and when I'm behind the gun I can't see it anyway.