I use nothing but formed CBC 24 ga cases,they are around 015 short on headspace,yet I have never had any issues shooting them.Primers dont back out,but stay put......the only fault of CBC cases,is they use pistol primers.......but rifle primers can be used for a few reloads until the cases fireform.Primers backing out a significant ammount indicates to me a block that is too short ,way too short.........and the commonest cause is a short replacement ,second commonest is grinding down to remove a primer ring..I cant see the gun in question,but the problems seem consistent with a A/stan bazaar gun.....not necessarily a KP,but an assembly for the punters.........US $300 is a kings ransom to an average Afgan.