I'd suspect, through experience, the man running the machine knows how many grooves the tool will cut before it needs to be changed. None the less, I also suspect, that the tool is inspected before the cutting begins on each barrel. While being sharpened, a different tool is in use. They don't stop production and wait on the tool to be sharpened. They probably have several ready at any given time. Still a shop that has a dedicated "tool room". where tooling is made and re-sharpened. A good tool maker can make several tools, all virtually identical. Remove one , install a sharp one. In my early years of production machining , when high speed was still king and carbides in it infancy, the tool maker made identical tools, remove the dull from the tool holder, install the sharp one, and send the dull to be re-sharpened. We changed tools on part count, how many had that tool cut. Only occasionally did we have to adjust the physical stops after changing tools. All tool sharpening done using specific jigs/fixtures to hold the tool, nothing done free hand, except maybe split the point on a twist drill. Back to the present, I happened to speak to Jim Hart one day on the phone. He still makes the buttons they used to rifle their barrels on a manual tool and cutter grinder, a K.O. Lee, I believe he said. Scoping a Hart barrel I can see no difference in land/groove profile from one one to another. Same can be done with cutters for cut rifled barrels. All it takes is a good tool maker....... And few exist anymore, now that most cutting tools come out of a plastic box.
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