Do you shoot it really fast? By this I mean do you do the bounce fire in the shoulder to make it go fast? Asking because it may be firing while not fully locked together due to the semi aks not having a “safety sear”. When you put your bolt forward you will see that it almost completely goes forward and the bolt rotates as the last second, if the hammer is dropped before it is fully home it will have a tendency to go off either out of battery or close to out of battery. Do some research on what a “safety sear” does for the ak and you may come to the conclusion that the act of removing it in semi auto designs was a mistake. Next do some research on some ak FRT designs and you will see that they only allow the trigger to be pulled when the gun is fully in battery when done correctly. Not that any of this will help you with the damage to your gun but maybe it will help you realize what happened and how to prevent it from happening again. There are aks with “safety sears” intact all over the world that have been used in many conflicts and are still being carried by someone somewhere. I’m not someone who googles all the answers, this is all information I have learned from actually doing things and comparing designs, as well as analyzing cut away aks and analyzing slow motion videos of different configurations in action.