What we're trying to say here is that any .40S&W Ruger SA cylinder can be altered by a gunsmith in a matter of minutes to be 10mm (or 10mm Mag, for that matter) by just boring the fat part of each bore where the shell goes, a bit deeper.
But the alteration is permanent, and won't allow the use of shorter shells.
There have been runs of .38-40/10mm factory convertibles made, and .38-40/.40S&W convertibles. So far as I'm aware, no Vaqueros ever shipped with all three, although I think some Blackhawks may have gone out the door that way long ago.
There was also at least one run of .40S&W Vaqueros (single cylinder only).
Any .40S&W cylinder can also be converted into .38-40 by a gunsmith, although it'd be a little bit harder than the dead-simple 10mm or 10mmMagnum conversions.
(Stupid question: if you were handloading .40S&W for the Rugers, you wouldn't need to worry about exceeding the overall length, would you? You could run an abnormally heavy round set a little bit shallow, run more powder to use the extra case volume you get that way, and make it perform like a 10mm, couldn't you? You've have to work up SLOW, keep it under 40,000psi, but...damn, a really advanced handloader (which ain't me yet, , this is just speculation at this point) could have some fun
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