Alot of surplus ammo is made to poor specs and/or degraded slightly. If you're shooting surplus, cracked/bulged cases isn't a huge deal. If you're firing factory Wolf, Brown Bear, etc. and it's doing it: I'd stop firing immediately and seek a qualified smithy to check it out. The Finn Mosins are usually pretty well made and won't do this with factory ammo.
-liberal gun nut = exception to the rule-
-1.24274238 miles, because Russians don't need scopes-
-Gun control was the Klan's favorite law, how can you advocate a set of laws designed to allow the denigration of a people?-