That's called counterfeiting.
Wrong-o, friend. Counterfeiting is printing something that you try to fraudulently pass off as legitimate US government issued currency.
Minting a one-ounce silver round for people to offer as a medium for barter at a suggested dollar equivalent is most certainly not.
Is it now illegal for you to offer to trade your TV set for my motorcycle? That's what the FBI seems to be proposing here.