I think your suspicion is right on with it. Those definitely look like tumbling or "keyholing" bullets. I bet the barrel has an irregular twist rate or the cylinder is out of time. May even have a defective barrel altogether.
A few years back century was guilty of producing polish tantals that were notorious for keyholing. Turned out to be over sized barrels.
A few years back century was guilty of producing polish tantals that were notorious for keyholing. Turned out to be over sized barrels.