Actually people it was an old Tippman SL68, or the pro carbine.
2 things give it away, it has a solid steel elbow attatched to the marker, and if you look at when fat bloke first pulls it from under his jacket, it has a steel loop used for a sling (in this case, removed).
And for the sake of realism, maybe they dropped the paint in the elbow as he fired.
And, it's not such a 'bad example' of painball being used. you don't hear alot of baseballers screaming about Joe Pesci beating up some dude with a baseball bat in a scorsese film do you!
Besides, any one remember the old Beneton adds?