The external crease in the tube allows the returning coolant and chips to be removed. Coolant flows out of the drill through one or two holes in the drill tip. The drill tip is available in various grades of carbide, depending on the material being drilled. The tip is not perfectly round. It is designed with two skid pads, which support the cutting action and burnish the resultant hole.
Machines are available specifically for gundrilling.
These machines have high-pressure coolant and are designed to provide superior concentricity. As the design of the tool is like a creased tube, it is not completely round. This can present some problems when rotating at high spindle speeds. This can cause the drill to whip, reducing both accuracy and tool life. Better results are achieved when rotating the part and not the tool.