#1421: Tortube

I’m disturbed by the number of times I come up with some idea to do with firearms. Anyway, today’s invention is an easier way to create a rifled bore ie without having to cut spiral grooves.

This involves driving a mandrel axially through a blank barrel. The barrel is then twisted around the central axis, to the point of slight plastic deformation, so as to distort the internal grooves into permanent helices.

The twistrate of these helices can be locally varied so as to optimise the rotational acceleration of the projectile being fired (ie as a function of the varying gas pressure behind it).


  1. One way it has been done for a very long time, a cutter is pulled through the bore. As it is pulled through, the pulling shaft has an arm that follows a track, or cam, to form the twist. Today it would be controlled electronically. The twist can be uniform, or start slow and increase the rate of twist. In the old days, one cutter was used to gradually reach the depth of the rifling, and the barrel was indexed to create multiple grooves. Modern methods include a ‘button’ that cold forms the grooves and do it in 1 pass. Twisting the barrel to form the rifling would deform and vary the diameter of the bore, very bad for accuracy.

    • Thanks for this. My guess is that you are right that twisting the barrel is another stupid idea of mine, although some kind of iterative twist-measure-twist cycle might be made to work, it seems hopelessly complicated.

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