Well, technically, none of them were using automatic weapons - or at least not in automatic mode. It only sounded that way when they all fired at once. Even civil war rifles will sound like that when a bunch fire all at once.
Think about it, they had 30 rounds between them. Even if it were only 6 people, that's only 5 rounds.
Any automatic weapon would expend that in about a half a second.
However, they still were dumb about it. They should have made rounds for something you can use a scope with and give 10 rounds each to 3 guys, each aiming for the "head" one at a time, counting off their shots in turn until they kill it.
Everyone else would get things like pipe bombs and molotov cocktails to at least hold it back and keep the fire off the snipers.
Paintball guns are semi-automatic - at least as they come from the store, anyway. You pull the trigger, it shoots a paintball. Repeat until you run out of rounds.
Now, something like TL Spyder with a two finger trigger can be fired very quickly and seem to be automatic, but it's really just the player pulling the trigger really fast. I can shoot up to 5 rounds a second with mine, meaning I could empty a 150 ball hopper in about 30 seconds. That, of course, is provided they feed that fast. The problem is, it's a gravity feed and the shells of the balls are made from gelatin - which makes them sometimes stick together in humid weather.
So, some of those 5 shots per second are just air.