Linked ammo typically wears the signature of the link rubbing the center section of the cartridge case.

Over on the subguns board some folks have noted very high failure rate in the form of case head separations when attempting to reload for the M60. This is brass fired from the 60, reloaded and fired again in the 60. The thought was loose chamber dimensions allowed for enough case stretch to significantly reduce case life. Maybe not such an issue if re-used in a tighter gun as growr experienced.