It is very common for an AK to make a mark on the brass, that is why most AK owners shoot steel cased ammo.
I have found that many times the bolt comes back with enough force to dent the shoulder of the next round, as long as the bolt goes closed on the next round there is no problem.(I don't reload)
I found this when using 40 or 60 round stick mags, the 75 round drum mags never had that problem.
I don't own a Saiga .223 but I have noticed a lot of bent .223 casings at the range I just figured that was where they were coming from.