I didnt mean it in a disparaging way, simply that you can walk into a supermarket and buy one.
Firearms laws vary from state to state. Las Vegas is in Nevada, one of the states with very little firearms restrictions. Florida is also quite unrestrictive. California and NY have the strictest laws.
Supermarket grade firearms? All AR15 platforms are built to the same spec as the original Armalite design from the 60's. The M-16 is the same platform, just that's the US military designation for it. In fact the commercially available stuff is often better quality based on the forging methods of the upper, lower and barrel.
Machine gun versus assault rifle? What? Anything that automatically feeds a round into a chamber using a gas feed system is a machine gun. It's the trigger grouping component that determines if it's full auto, burst or single shot.
Barrel length making it easier to aim? You think a 5.56 or .223 round magically stops after 300 metres on a short barrel? 10", 16", 19" barrels are all going to reach out and stop something.
Don't believe everything on Wikipedia.