Hey all. I think that Pdq is talking about a machine gun being a belt fed or large magazine fed high caliber weapon like the kind used in the trenches or WWI WWII and Korea to mow down the enemy from fixed positions. They were also mouted on propeller driven fighter planes.

The ar-15 on full auto, as Bobert describes is called and assault rifle. It has much smaller, slower bullets and the magazine, that is the number of available bullets available without a reload is smaller. I have to disagree with bobert on the difference between full auto and semi auto. Full auto is a lot more sure of a kill with an Ar-15 or AK47. Short burst are fired the victim can receive three to five shots, basically before a person can move to duct or run.

In between is the "sub machine gun" such as the Thompson gun which has 45 caliber pistol rounds and generally a larger magazine than the assault rifle.

I don't know these things from experience but I've drank with some gun nuts and military types in my time,