My immediate comment to him after seeing these 243's was to stop shooting, check the rifle for damage, and dispose of any remaining rounds. I looked at a couple of unfired ones, same headstamp and they exhibited turquoise colored corrosion around the neck to bullet junction. Don't know about the origin of the ammo, but Remington-Peters has not been around for a long time. Must've been some very old stuff exposed to humidity at some point.
Scary.....