Drilling is among the simplest of machining operations. Drilling by hand or machine power produces a hole, which may be the final result or the start of a subsequent operation. The drill bit is typically a rod with a sharp working edge at one end. Any cutting process produces residue. In machining, the residue is called chips that must be cleared so the tool will not bind. For metalworking drills, spiral cuts running up the drill shaft act as ramps to lift chips out of the hole so the drilling can continue.
Most drilled holes in firearms are of little concern to the firearm examiner. However, one is of critical concern to the examiner - the hole through the barrel of a handgun or rifle that marks a fired bullet. The deep hole drilling operations performed on rifled gun barrels form the foundation for the unique characteristics of each gun barrel that makes firearms identification possible.
This hole is drilled in practically all firearms made in the last 150 years. Deep-hole drilling is a challenging task that requires excellent tooling design and manufacturing techniques. Without such attention to detail, the hole will not be straight and the barrel may never shoot accurately.
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