In 1950, early in the days of AK development, there was some experimentation done with muzzle brakes, in an effort to reduce muzzle climb and improve accuracy (as well as full-auto controllability, I expect). From the Soviet Gun Archives blog, I found this photo of a half dozen different devices tested:
“The positive effect of the muzzle brake on the accuracy is at odds with the negative result of the sound wave hearing, which is greatly increased to unacceptable levels with most muzzle brakes.…The evaluation of the effect of the sound waves on hearing reveals that all muzzle brakes in the table result in a bothersome or painful sensation in the ears.”
I find it quite interesting that these experimental brakes as a group bear quite a lot of resemblance to the commercial brakes many shooters put on competition or “tactical” rifles today. In particular, I find it entertaining to consider that 1950s Red Army officials were more concerned about shooting comfort and hearing than modern competitors. Of course, this isn’t really a fair comparison; the Red Army was working as a group and not using hearing protection while modern sport and competitive shooters use very effective hearing protection and don’t do anything that requires cooperation or complex communication with other people while shooting. Today’s type of competition shooting simply doesn’t reveal the full consequences that the jarring concussion of modern “tactical” muzzle brakes would have in a more realistic situation.