K, here's the idea, a 30 or 50 caliber gun. Except, you don't carry it in your inventory. It's placed somewhere on the map. You can get on it and shoot it, but it remains in its position. I think it'd probably be easiest to do this as a vehicle, so it would just sit on the spawn point and not be able to move (though you'd need to be able to fire it and rotate slightly as well as move up and down hopefully to aim). Overheating, jamming or a reload after expelling a few hundred bullets would also be a nice touch, allowing attackers to surge forth in those few seconds.
