Well, I'm stumped. With the brake installed it groups 3/4" to 1/2" centered with the load it likes best with the brake and (with the brake installed) 1 to 1 1/2" close to center with the load it likes best without brake. All SMK 175 gr. bullets. Take brake off and adjust scope back to where it was zeroed without the brake and first shot is 4 1/2" low, second shot 2 1/2 " low, third shot 1 1/4" low then back to grouping. Did it with both loads several times several different ways every time the brake is removed, with and without the thread protector installed, clean or dirty muzzle and clean or dirty bore. Went through 100 rounds. Every time the brake is reinstalled and scope dialed to zero it goes right back to grouping POI = POA on the first shot.Take it off it's three shots back to POI = POA. I give up! Some sort of "CRAZY" harmonic going on when the brake is first removed. I've decided to just load for the brake and leave it on.
Guns are not dangerous! People are! RKBA!