Most conventional drilling operations have limitations on how deep the drill can go. The depth limitations are applied due to the need to cool the cutting edge, transport away the swarf and the strength limitations of long, slender drills.

Deep hole drilling or gun drilling is a specialized operation used to machine long, slender holes. The process often uses specially designed drills and machines designed to assist the removal of swarf from the cutting edges.

Applications for this type of drilling include gun barrels, lubrication holes, oil passages and fluid channels, or anywhere a hole beyond the depth range of a conventional drill is needed.