A lot of FAL guys had this problem with their rifles and they fixed the problem fairly easily with nothing but a file and a couple of empty shells and duct-tape.
The issue on denting brass is the rate of spin the ejector forces on them. I'm not talking about the claw on the bolt face, obviously, I'm talking about that piece of metal that catches the edge of the brass as its pulled back by the extractor and is kicked out by it the protruding metal. Most ejectors are stamped steel,
The basic concept is to lightly tape duct tape to the area suspected of denting the brass and put an empty shell into the chamber and rack the bolt as hard as you can to simulate the gun kicking out a shell to create the denting on the duct tape. Then, with a file, file off (very carefully I might add) the metal towards the outside of the reciever in a 90 degree fashion relevant to the base of the rifle. This will make the brass eject in a slower spin the closer you make the contact point, that meets the case each time, more towards the inside of the case. Filing the upper or lower edge of the ejector will effect the brass's path on its vertical plane of movement.
This is a shortened tip to how to fix the problem, but there is a detailed guide on fixing a FAL's ejector angle that can generally be applied to AK rifle ejectors.
This is the link to the guide-- FNFAL RIFLE EJECTOR ANGLE / ELIMINATING RECIEVER BRASS STRIKES
This same guy also tells you how to widen the rails of the reciever on an FAL, it worked sort of for me but I KNOW the ejector guide works because I did it myself.