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Old August 27, 2012, 01:42 PM   #1
Senior Member
Join Date: May 22, 2007
Location: Arizona
Posts: 4,437
Need some quick info, 40SW barrel diameter

I slugged a 40 SW pistol bore, came up with .402. Factory bullets are .400/.399, on the few I've looked at. Factory bullets gave unimpressive accuracy. Cast bullets sized industry standard at.401 gave mediocre accuracy and bad leading.Oversize cast bullets sized at .404 gave excellent accuracy and minimal to no leading.
Question, to 40SW owners who have slugged their bores, it this the same diameter you have come up with, groove to groove? Groove depth is approx .003, so a .400 bullet has .001 to engage the rifling, not counting obturation, which I would have to assume is minimal with a jacketed projectile.
The factory representative refused to give me the information over the phone, wouldn't even say whether or not such a diameter is within factory specs, so I ask you, the experienced casters and re loaders, is this a normal diameter? Not mentioning the manufacturer until I get some good info on whether I am wrong or right, and I've been wrong more than once before.
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