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I doubt a mass production broach operates that way.
I have seen pictures of factory broaches several feet long with many cutters, each a little larger than the one before. One pass through a starter hole cuts to final shape and dimension. Pedersoli rifles that way. So did Smith & Wesson in the good old days. Single cutter rifling was too slow and buttoning an asymmetric forging does not give uniform groove depth. Of course they did a lot of lapping when done to get rid of the broach marks.
Mr Garand not only designed autoloading rifles to be shot, he designed them to be manufactured, based on his background at Browne and Sharpe. The Hot New Thing in 1930s manufacturing was the multiple step broach as an improvement over lathes, mills, and shapers. So he designed his rifle to make maximum use of broaching, minimum single point cutters.
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