Careful with that one. If NY considers muzzleloaders to be modern firearms, you might land yourself in hot water. When shipping modern guns, the frame/receiver/serial numbered component is considered the actual gun under the law. If NY is structuring their laws regarding muzzleloaders under federal standards for modern firearms, you might be breaking the law unwittingly by shipping a "complete firearm" by sending out the numbered part, regardless of whether or not you sent the item in two or more packages.