You could just as easily say that at the time it was written, a private individual could own any weapon in the inventory of the best-equipped armies and navies of the world at the time, musket, rifle, pistol, cannon, carronade, howitzer, mortar, or grenade.
At this point it remains totally unclear what role the high-capacity thing played, or even the handguns, all we know is the dude had three handguns and a longarm, types unspecified. Nor do we know if he got them at yard sales, swiped them from family or friends, borrowed them, or even bought them with a full background check.