Note 114 — Chapter VIII · THE RIFLED GUN
Reading edition
In this aspect of the origin of the grooves there is a curious analogy between the rifle-barrel and the drill used in machine tools. In the primitive drill the shank is appreciably less in diameter than the hole cut by the drill, so that the drillings can easily work their way out of the hole. When, however, it was desired to make the shank almost of the same diameter as the hole, so as to form a guide, it was necessary to flute it with two grooves or more to allow the drillings to get away. In the course of its evolution these grooves became spiral.