Civilians generally cannot own artillery (sub)machine guns, any firearm intended to be fired with 2 hands with a barrel less than 16” in length (the wording on all this can be very complicated legalese), suppressors, or explosives. Incendiaries are state by state.
Not true. Owning a item covered by the National Firearms Act (NFA) is not all that difficult for law abiding citizens.
The NFA regulates ownership of shotguns with an overall length of less than 26" or a barrel less than 18", a rifle with an overall length less than 26" or a barrel less than 16", weapons capable of automatic fire, suppressors, and explosive devices.
The process is simple and straight forward. It's time consuming, because it involves multiple government agencies. I've made a detailed post about the process elsewhere. The short version is that you buy the item and it sits at the FFL dealer while you do paperwork. You get a signature from your local sheriff or judge, send that with more papers to the ATF (along with $200), they forward part of it to the FBI for the background check, and when it's all done they send it back with the tax stamp.
To get any of those weapons you need a special tax stamp, and they’re almost all extremely expensive generally.
Not true at all. The tax stamp costs $200, which is not prohibitive at all for the vast majority of people. Especially when you consider the other costs. My bedside gun is a Glock 41 with TrueGlow sights, TLR-4, Pyramid trigger, Lone Wolf extended/threaded barrel, and a SilencerCo Osprey 45. So I've got about $2000 invested in the hardware. That $200 is no big deal
A legitimate machine gun or sub machine gun will cost about as much as a new car, or a even a small house.
Also not really correct.
Automatic weapons are divided into two categories. Pre- and Post-1986 manufacture.
The road to owning a Pre-1986 weapon is the same as any other NFA device. Buy it. Add one more form for a "Curios & Relics" collector license. Get the tax stamp. Take it home.
These weapons are scarce, and collectible. That drives up the price. A full-auto pre-1986 AR-15 might well cost you $30,000. That won't really buy you much car, and certainly not much of a house.
Or you can spend $150 for a three year Class I FFL. Pay an additional $500-$1000 per year to upgrade that to the Class III FFL SOT. Now you can buy a brand new full-auto AR-15 for $1500.