rifle drilling is a process that produces deep, straight holes in a variety of materials. A rifle drill tool differs from a conventional twist drill by its unique head geometry; a standard rifle drill has a single effective cutting edge. Guide pads burnish the hole while drilling, allowing the hole to maintain straightness. The result of this burnishing activity is a very round hole with a precision diameter.
when drilling with a normal twist drill you will get drill wander and a slightly ovaal hole unless reemed. the gun/rifle drilling process is much more accurate but slower band more expensive but overall much better.
another process that can be used is using slip collars after drilling which are pullled through a drilled hole to prevent star cracking around a hole.
i previously worked in london undergrounds machine shops producing points and crossings and all these process were used
