Are there any? Public or private.

What type of NFA? I don't think you will find any that are grenade launcher friendly, but suppressors are a different story.

m16

IIRC, a lot of ranges even try to restrict rapid firing of SA pistols and rifles. They're afraid of an incompetent shooter letting the muzzle climb and getting above their berms. I know I've seen signs prohibiting this at GunSmoke. If they're "officially" intolerant of even rapid firing a SA rifle or pistol, I doubt they're going to be to open to full auto mag dumps.

Your best bet is going to be to call around. Or find some private land.