When a cartridge does not fully chamber in a model 60, it will cause misfires and bulged cases just below the rim.
This is usually from a dirty chamber. Shooting non LR ammo like shorts will create a ring in the end of the chamber. I've also seen old grease/oil that hardens enough to create a cushion effect in the chamber, absorbing part of the energy delivered by the firing pin.
Some work with some solvent and a bore brush in the chamber can clear it up.
