So far deep hole drilling( gun drilling) has been used more and more widely in injection molds. This method requires a special machine or a deep hole drilling adaptor to another machine, such as a milling machine. The drill operates in a horizontal plane. There are four essential differences from ordinary drilling or milling machines:

1)    The stroke of the machine(depth of hole) can be considerably larger.
2)    The drill is supported very close to the work piece, as with a drill jig.
3)    The cutting edge of the drill is directly, pressure lubricated.
4)    The drill works in one pass through solid material. It does not require predrilling.
There are two types of drills, featuring either internal or external chip removal. The external chip removal method is mostly used.