There are no Federal laws restricting it's sale - by Federal law you can sell it and mail it to someone's door just like a muzzleloader. No FFL needed.
HOWEVER, as is always the case, you have that whole "powers not delegate to the feds are held by the states" gotcha. Depending on the state your in, AND THE STATE YOU'RE SHIPPING TO (if selling online), there may be additional restrictions in place above and beyond what the Feds require. Make sure you read the laws of your source and destination state carefully.