Re: Stamped brass
FC = Federal Cartridge, and that's the way that FGMM brass is stamped
BHA = Black Hills, and it's made by Winchester.
If you bought "all FGMM brass" from someone it's not what you got. BHA is still good brass and I personally like Winchester brass better than Federal but you can work well with either. Don't expect that the best load in the BHA will work in the FC and visa versa. My experience trends that the BHA will have more capacity than the FC and a "warm" load on it could be sneezing primers or worse by switching to the FC. This is why it's always recommended to "Reduce and work up" when changing a component in a load.