Full auto weapons are legal to own and use. It requires some paperwork and paying some extra tax. The incidence of gun related crimes committed by folks who do jump through the hoops to legally own one doesn't even register on a graph. So, if you happen to know someone with a legal full auto, thats one guy or gal that isn't a likely threat.
Correct, I owned 2 "class III" firearms. It's a matter of a $200 tax stamp, and being cleared by your local LEO to be able to own it (form 4)It must be a transferable gun (built pre 1986 if your a non FFL lic. Holder)
You must also have the paperwork available for inspection by any Fed or state LEO upon request. Ie if you go to the range the paperwork goes with you.
Making the AR full auto isn't all that easy , it's the matter of a sear change, bolt carrier and disconnector. Thing is guns post 1986 are near impossible to do it to, and the above parts I've mentioned are all Class 3 components. Look to spend in the 5 digits range if you want to get into the full auto game.
Edit......Corrected should have said owned....have a mortgage wife and twins now.....they were sold when the kids were born for a hefty down payment on a house.