Quite some time back I had a screw-on brake installed on a barrel. The gun was super accurate. After putting on the brake I took it out and while the accuracy was the same, the POI changed quite significantly. By about 2-3" @ 100 yards. I figured the gases escaping around the projectile while passing through the brake were deflecting the bullet slightly. Always had to insure if shooting with the brake you kept it on there tightly as the clearance in the threads when loose affected both accuracy and POI.
