I have 100 220grn full metal patch bullets which are pulldowns from 30-40 military ammo, I think. Quite by accident I discovered 9 of those bullets have an alloy core containing iron or possibly an insert. Bullets are all tarnished to some degree but the 9 mentioned are still pretty much bright copper. The 9 are, on average 1 grain heavier. All 100 have the cannelure. I don't want to dissect any of them so, any ideas what I have???