By recommendation of my gunsmith I went with a 7/8" 9/16"by32tpi harrel precision 4 port tactical brake, for my 338 ultra mag. I have been shooting 300 Bergers with rl 33 getting an average 2840 muzzle velocity that hot of a load out of my light weight rifle seems to just beat the hell out me I shoot a group of my loads then shoot my fathers 7 RUM with 175 LRAB loaded to the nuts and it barely has any recoil at all. Now to the point I am in need of a more effective muzzle brake!! Any and all recommendations are appreciated thanks! Ps it has to be 9/16x32tpi