Not all states permit "class 3" weapons but most of them do. The total number of "class 3 permits" (you have to have one for each weapon)has been frozen, I think at something like 52,000 total. So the supply is not unlimited, and the price has gone up considerably since the limit was imposed. Expensive little devils to shoot, who can afford it? There's also a restriction on size, 55 caliber is as large as a civilian can own. There are a few old semi-auto anti-tank rifles around in that caliber but they are hellishly expensive to operate. Civilians cannot legally own "destructive devices" like mortars, rocket launchers, or breech loaded artillery. You can however buy muzzle loading artilllery, original or replicas, because they fall into the 'antique' category. For about $25,000 you can buy yourself a twelve pound Parrot rifle that will make some serious noise and hit something the size of a car a couple of miles away.
In my state there is no waiting period on rifles and shotguns. Only certain benighted Communist States like California and New Jersey differentiate semi-automatic rifles as far as purchase or possession. Hey I've got an SKS as well, ugly critter but it's reliable. I've got one of the Mini-14s, it looks a little like the M-14 from the outside but it shore isn't.
"I'm the NRA"