Gunsmithing Fat Bastard muzzle break

[DerekD337]

I just bought a Fat Bastard muzzle break from APA and have a few questions about threading my barrel. Im a machinist by trade and own a big machine shop with all the equipment needed. Would anyone have a print or drawing showing dimensions and lengths to turn the barrel so it seats right?? Inside the break, past the thread relief, its got a about 32' bevel(I poured a mold and checked it on a compariter). should I bevel the end of my barrel with about .002 clearance so it will seat against the bevel inside the break and also shoulder up against the shoulder behind the threads on my barrel?? Or should it ONLY shoulder up behind the threads on my barrel??
I would really appreciate any advise I can get!!
Thanks alot
derek

 

[JB Enterprise]

Re: Fat Bastard muzzle break

Hey derek if it is a standard thread 5/8-24, the barrel is threaded for 1/2 of an inch from the muzzle, just use a standard relief on the front of the barrel I fit all of my muzzle brakes with a class 3 fit for the reason that the threads locate the rifle barrel to the bore of the muzzle brake.in order to time the brake you will have to shave off of the shoulder of the barrel for this is the surface that will locate the muzzle brake not the muzzle end of the barrel. This process also works with any thread not just 5/8 if you need anything else just ask.
Justin Bowerman

 

[jasonixo]

Re: Fat Bastard muzzle break

Hi Derek-

Ideally, .600 is a good thread length. Because the shoulder needs to be shaved to index the brake, thread the muzzle 5/8" x 24tpi x .575" long. After you index it, you'll be pretty close to .600". Be certain that you dial in the barrel coaxially with the bore and that you bore the brake .030" over by screwing it on the barrel in the same setup as threading it. You can crown the muzzle any way you prefer. Cosmetically, the FB Brake looks pretty good with the back end chamfered somewhere around 10-15 degrees tapered toward the barrel. Feel free to call the shop if you have any questions!