Suggest you look at this web site:
http://www.michigan.gov/msp/0,1607,7-123-1586_27094-10953--,00.html#Pistol_Registration__Purchase____Transfer Specifically, the official state web site says, "A License to Purchase is not needed ...for relics, curios, antiques, etc., not made for modern ammunition."
Also, with regard to registration, it says, "...antique pistols made before 1898 and replicas of antiques that use black powder, matchlock, flintlock, percussion cap or similar type of ignition system do not need to be registered."
That being said, I have in fact registered all my C&R guns just for the "official" sanction should they be lost, damaged or stolen. And, frankly, to reduce the hassle from the occasional LEO that does not know the law as well as he/she should. I made that decision when I asked the local sheriff's office if I needed to register a C&B pistol I had purchased at auction. The pistol had been registered by the original owner, but the auction house said they would let me take it without a purchase permit as long as it was declared a "wallhanger". Well, with all that nonsense going on I felt I should find out what the requirement really was. The sheriff told me as far as they were concerned no registration or purchase permit was required "as long as the gun was not going to be fired." Essentially, don't get caught wandering around the woods with a C&R gun and ammunition that fits it if it wasn't registered. I also spoke to my CCW instructor and his lawyer, and both advised me to go ahead and register the gun, plus several others that I had purchased years ago in another state. The lawyer said I'd probably win any legal confrontation, but why go through the hassle and expense (here's a lawyer saying why pay me when you don't need to).