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Close Up of a photo a rifling broach tool
Rifling broach
Photo Courtesy of FirearmsID.com (see reuse policy).

Broaching uses multiple cutting surfaces (cutters) mounted on the same axis to progressively remove metal. It is used for critical operations where precise angle or depth control must be maintained. After the first cutter, each successive cutter is a few ten-thousandths larger than the one before it. Each cutter shaves off a small amount of metal, reducing the applied force.


photo of a cutaway of a gun barrel
Broached rifle barrel
Photo Courtesy of FirearmsID.com (see reuse policy).

Most firearm examiners will recognize the word broaching from its use in the manufacture of rifled gun barrels. Broaching is one way to produce the spiral grooves needed to spin-stabilize a bullet. A rifling broach has circular working nodes, each with a reverse profile of the rifling pattern. As the broach moves through the barrel, each node shaves off a little metal. The next node is slightly larger and rotated from the previous node to match the desired rifling twist. Broached barrels made with quality tooling have very straight bores and are capable of fine accuracy.

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