Not that any of the other responses are incorrect, I would not trust legal questions to be answered on a forum. Go to the specific web site for the State concerned and look up that State's firearms laws. This should keep you out of trouble most of the time. Good luck.
In most states you can purchase black powder handguns without a permit, as well as ball, cap, and powder. The catch-22 is that while you may be able to legally posess the gun and all components, in NY atleast, you cannot shoot it without a Permit. Many Police agencies are not even clear on the laws governing BP. Check your local Gov. website, but for the time being err on the side of caution and assume you cannot.
I know that the Feds say that you can have a firearm produced before 1898 or a replica of any firearm produced before 1898 (cap&ball etc.)without a FFL or any other permits, But I'm really not sure about Michigan's laws.
I assume by your question you mean to sell as a dealer? Do you have a shop or store front? Michigan is pretty strict about dealing in a school zone!
Seen a sign once in a mans yard. GUN NUT, by sell trade. Once I got passed the dog he did had a couple. Didn't take long for the sign to come down as he did not have a FFL.
Being strict has nothing to so with it. You can't sell guns on your front lawn like your selling lamps in any of the 50 states. He's lucky the police let him just shut it down. Selling or trasfering a gun without going through an FFL dealer is breaking federal gun laws. As a "gun nut" he should have known that.