The combustion gasses exiting the muzzle of a rifle are extremely hot, traveling at extreme velocity, and contains not only burning gasses but solid particles of unburnt powder as well as metals from the projectile. Due to the inherent nature of steel, it is nearly impossible to survive unaffected in this environment when directly exposed. The high temperatures begin to make the steel more malleable, which allows solid particles and pressure waves to deform and erode surfaces upon exit.
Due to the new and unique design of the BCM compensators, the user may notice small pits on the interior surfaces of the compensator. This is normal. Most designs do not impede the exit flow very much, while the BCM approach is exactly opposite. These surfaces are specifically designed to operate within the environment found at the muzzle, and are intended to allow significant amounts of deterioration before any loss of performance is seen/felt. These compensators have been tested through many thousands of rounds, and while the wear surfaces may give pause to some users, trust when we say that it's normal.