In the .40 mags, there is a little spacer in the back of the tube, such that the front of the cartridge is at the same position as a 10mm. The feed lips for the two are identical. The .40 S&W will work with 10mm mags, but not the other way.
Anybody looking for .40 S&W single stack magazines? I have six Metalforms I may will willing to part with.
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John
[This message has been edited by John Forsyth (edited 01-19-2001).]