quote:

Originally posted by GP229:
It will fit in there, but the breech face will be wider than the barrel hood, so the barrel may not lock up the same every time it goes into battery.

The slide stop may not contact the follower on a 9mm magazine not locking the slide back after the last round.

9mm may work in the .40 magazine depending on the magazine itself.

I did it just to see if it would work, but it was only a handful of rounds at the range. I have both a 9mm and a .40 so I was just curious after all of the times this question came up. I wouldn't even consider it a valid test and would not recommend trying it.

If this is a gun used for personal defense, scrap the idea and just buy the right gun!