What about a rifle in the hands of a 1770's militiaman?
The common military long arm of the day was a smooth bore musket, but rifles were owned by civilians. In the 1870s the army was still using single shot rifled muskets but a private citizen could purchase a 15 shot level action from the Sears & Roebuck catalog. During the 1920s the army turned down the Thompson submachine gun, but private individuals could purchase one with ease.
Up until the 1960s, the public has always been better armed than the military as far as small arms were concerned, and registration was never a concern.