Can check shot with a magnet. For waterfowl hunting, a larger steel shot size is used vs. lead shot to keep about the same weight per pellet. Smaller steel shot, due to its lighter weight vs. lead shot of the same diameter, does not penetrate feathers so well. The Federal ban on using steel shot for waterfowl hunting began with the 1987-88 season. Your shells are unlikely to be from much earlier than that, and probably later.