Well I ordered a new firing pin and it is works most of the time on Prvi Partizan ammo so I thought I would try Sellier & Bellot and first shot PING!! Case rupture! I don't think it hurt the rifle and it vented as designed. So I'm back at wondering if the chamber has been over polished or rechambered to something close to 6.5x57 or is it a 6.5x58P. Gunwolf had mentioned 7x57 very early but I don't think the bore is big enough for that. I would really like to get it up and running.