HSM is, as stated, a company in Montana that manufactures ammunition. IIRC, their ammo (or at least a portion of it?) is re-manufactured. That's probably why their brass has the NATO cross on it.
I have a fair amount of mixed military brass from surplus loaded ammo I've purchased and shot. Various years from LC, some TZZ (who is TZZ?), a little WCC. It all weighs the same as most of my PMC brass, though I do have a few leftover PMCs which are WAY heavier than the rest. Interestingly, my FC (Federal Cartridge) brass is a few to several grains heavier than the surplus and most PMC brass I have.