I've bought & used them. I bought pilots to do the cylinder opening (charge holes) & ones for the muzzle/crown.
When I did the charge holes it was hard to keep it smooth & it wanted to leave ripples. Those can be smoothed out with the lapping tool & some abrasive grit though. (I later bought some 600 grit compound, not shown.)
Good advice on not chamfering the extractor. For some reason S&W doesn't do that as every pistol the factory has done included the extractor. I took mine out before I chamfered.
I've used mine more for cleaning up the muzzle/crown than the charge holes. While it's made more of a difference in accuracy in some more than others, I like the look of a chamfered muzzle much better than the abrupt opening.
Don't skimp on the cutting oil either, use a firm but steady pressure & clean the cutter (metal shavings) frequently. Go slow, you can always remove more later.
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627-5 PC, barrel crown, before chamfering
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627-5 PC, barrel crown, after chamfering
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69 Combat Magnum, after chamfering
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Brownells Chamfering Tools (-01a)
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Brownells Chamfering Tools (-02a)
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Brownells Chamfering Tools (-03a)
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