Gun Drills

Gun Drills are used for deep bores. And are usually equipped with channels for feeding coolant from the base to the end of the drill. Using a normal drill would not work because the flutes are not long enough to evacuate chips and flood the cutting surface with coolant. Drills are available in straight or spiral flutes (spiral drills are made by taking a two flute straight drill, heating, and twisting).

Here is a link that talks about making air gun barrels. Kind of a good description.