It was RIA who developed the idea of a Broached barrel for the carbine. Underwood seems to have been the leader of it's use as the amount of time and work was very small compared to the standard methods of cutting rifling into a barrel. Not all of the makers of carbines used barrels with the broached rifling. It was found to be as accurate as cut rifling and with just two passes with the equipment to rifle a barrel at a rate of 50 an hour compared to 11 an hour with the cut rifling system. A big improvement and one of the reasons Underwood barrels were considered to be the best of the Free Barrel progam.
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