Heller concluded the Second Amendment protected the right to possess a handgun in one's home, because handguns are a "class of 'arms' " overwhelmingly chosen by American society for the lawful purpose of self-defense (Heller, at pp. 528-530) and were the type of small arms " 'in common use at the time' " (id. at p. 627) that citizens, when called to militia service, were expected to bring with them when called to serve. However, Heller simultaneously approved Miller's observation that the Second Amendment does not protect those weapons not typically possessed by law-abiding citizens for lawful purposes, and specifically referenced M-16 rifles as weapons that could properly be banned without offending the Second Amendment under "the historical tradition of prohibiting the carrying of 'dangerous and unusual weapons.' " ( Heller, at p. 627.)You see what they are doing here, of course. They are freezing what are "weapons in common use" through a circular argument. That is, the ban is being upheld because the firearm is not "in common use" (although that is debatable); but because of the ban, the weapon can never become one "in common use."
They are also being intellectually dishonest by comparing a semi-auto AK rifle, owned by the defendant, with the M-16, which is a select fire weapon (i.e., automatic weapon). This, even though in order to be imported, the rifle had to have passed the federal government's "sporting use" test, and thus one that could lawfully be used for hunting. In fact, but for the ban, there doesn't appear to be any indication that the defendant could not have lawfully used the weapon for self-defense or hunting, or that it would have been inappropriate for use in a militia.