Dear Mr Duke - First you start off with a long drill that makes the starter hole, then you cut the rifling 'flats' one by one until you have completed the six-sided bore. You don't 'force a hexagonal spiral cut down the length' of the gun barrel - the cutting tool [it looks a bit like a witch's 'snaggle tooth'] is pulled through the bore in a spiral motion from the breech end to the muzzle.
Is this what you wanted to know?
tac