So why not buy illegally now?
Because most illegal stuff is junk. I have no need for an UZI or MAC-10 because both are inaccurate and machine pistols are stupid to begin with. Revolver shotguns like the Taurus judge in my opinion are also stupid because they can break your wrist.
Legal stuff like the AR-15's and AK47/74's are overhyped and overused, I'd the Ruger 14 take or Ruger 30 because they don't look like military death machines and they fire the same rounds. The Ruger 14 can fire .223 or 5.56 if specified, the Ruger 30 looks the same as the 14 but fires 7.62x39mm.
This may look like an m4, but it is a civilian rifle.
It might not look like much, but it can fire the same ammunition as the rifle above as well as feed the same magazines.