I would NOT use crush washers with a suppressor - it will increase the odds of getting a baffle strike.Get a bag of high quality 5/8x24 crush washers, and run one behind the brake against the shoulder at the muzzle. Be careful not to over clock during install or you'll need another washer. Put a lil loktite or rokset on the muzzle threads. You're done.
I could see that being a possibility with a factory rifle or sub par smithing of the muzzle threads and their relationship to the bore.I would NOT use crush washers with a suppressor - it will increase the odds of getting a baffle strike.