Cut Rifling: A cutting tool is drawn down the bored barrel in a helical fashion by a rifling guide. The cutting tool cuts the grooves, leaving the lands. Every few strokes, the cutting tool is readjusted to make a slightly deeper cut until the proper depth is reached. Each groove is cut separately; very precise but time consuming. Used by Obermeyer, Lilja, and Krieger,and Shilen, among others, and can be used on any contour barrel.
Button Rifling: A carbide 'button' is drawn through the bored barrel by a hydraulic ram in a helical fashion by a rifling guide. The button swages the grooves into the barrel metal. This is very quick; it takes only about 20 seconds to rifle a 30" barrel. The barrel must be a straight contour end to end and then turned to profile after rifling. Requires a different button for each twist/caliber. Hart barrel, Spencer Barrels, among others are button rifled
Broach rifling: A broach, or graduated file, is pulled through the barrel, cutting the grooves in one pass. Not used much anymore as the tooling is fragile.
Hammer forging: An oversize bore barrel is slipped over a mandrel bearing the negative imprint of the rifling; the barrel is then literally hammered down over the mandrel by a hammering machine. The mandrel is then twisted out, leaving the bore. A popular method of producing factory tubes.
A couple of terms:
rifling guide: a cylindrical bar of metal with a helical groove corresponding to the twist rate of the barrel cut down its lenght. This indexes into a headstock on the rifling machine and controls the twist of the rifling head or button or broach as it passes down the barrel.
lands: the raised part of the rifling (duh)
grooves: what's left.
Barrel production is a very equipment intensive process. You require a deep hole drilling machine to bore the hole in the blank barrel stock, a lathe to ream to size, a rifling bench to perform the actual rifling procedure on, barrel laps, heat treat oven, to name a few. Easily a $100,000 endeavor to set up, and that's just with manual machinery. Think about that the next time you wince over a $250-$350 price tag for a premium barrel!
Enjoy!
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