A friend of mine is a convicted felon, he checked directly with the BATFE in Washington, DC, he was told that he could in fact own muzzle loading guns because they're considered "primative" and not the same as cartridge firing arms. He is prohibited from being in possession of any gun that fires a self contained metallic cartridge, including shotgus, but not muzzle loaders. There is no federal restriction against him owning archery gear. though some states may have their own restrictions.