[yarddog]

Your post piqued my curiosity so I got out my loading manual and checked the cartridge case dimensions. Unfortunately my newest manual does not have the .40 S&W.

I got out my digital caliper and measured the case dimensions of the 10mm and the .40 S&W.

The 10mm measured .424 at the case head and .421 at the mouth. The .40 S&W measured .421 at the head and .420 at the mouth. That is darn near a straight walled case and I am surprised they feed as well as they do.

It did strike me that the .40 S&W (Both cases were R-P) is slightly smaller and would likely slide down the chamber a little. The extractor would probably keep it from going far but it really does sound dangerous. In fact really dangerous.

Like you, I might try it in a real emergency but nothing short of that.

[P8riot]

Yeah, I lurked into a conversation on a gun related board (don't remember which one) a few months ago (I guess) where the question came up, and several people there were saying that they had no problems doing it (on a regular basis) in their 10mm Glocks, but it just doesn't sound right to me. In a pinch I'd say yeah, but I'd never take it for granted that it was OK.

I don't shoot 10mm regularly, although I have several weapons chambered for it. My primary carry gun is a 9mm, so Im not likely to be in a position to have to depend on substituting a 40S&W for a 10mm.

[B4Ranch]

Just looking at the numbers I don't think three thousandths would be noticeable to anything but the firing pin in relation to servicability. .003 is about the thickness of a dollar bill.

This is assuming that both cartridges have the same bullet in them with the same protrudence. A sloppy or worn chamber on the 10mm weapon would be one place where there could be a more signifigant forward slippage of the .40 S&W that would be noticed.

yarddog, would you measure some fired cases and post the numbers for us?