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So, my wife and I decided that we wanted to sell our Sig P239s and replace them with M&P9s. Then the question arose about caliber conversions.....especially seeing as she would like to consolidate calibers, and liked the fact that the M&P45 gave us more rounds in about the same size package as a 1911.
Now that got me thinking about possibly going from 45 down to 9, in the same frame....... And after thinking about it a while (and knowing it isnt a simple barrel and mag swap, like 40 to 9) I was thinking that maybe one could switch the slide assemblies and insert a spacer into the mag well (or replacement spring, follower and spacer into an M&P45 mag to accommodate 9mm). Theories and input would be greatly appreciated

There's probably too significant of differences to make it work reliably. I've got a 45 & 40 at home. I had never thought to try to swap slides, but I do have a 9 barrel/mag for my 40. That fires reliably! If the slide didn't say 40 on it, you'd never know. Wonder if someone does engraving to add a '9' to it! ;)

40/9
40&9
40-9

Hehehe, M&P 409. Like the cleaner. Gets it all done . . .

What's you're ultimate goal in this?

The 45 is a larger frame size so it won't work. As mentioned above a 40 can accommodate the 9mm and the 357 SIG by simply swapping barrels. In reality, there is very little difference among the 9mm, 357 SIG, 40 S&W, and the .45 ACP for self defense. I own two 1911 pistols that rarely get carried I carry either an M&P 40 or a G19 and don't worry about the effectiveness of either caliber.

Thanks for the info. Thought experiments are always fun, and some tend to get expensive.....and I am sure that my wife appreciates the fact that now I don't have a "reason" to get both

40 to 9... I would have thought you'd have to swap the recoil spring also.

Maxwell wrote:40 to 9... I would have thought you'd have to swap the recoil spring also.

The factory recoil spring is the same for all three calibers. That's what I run in all my M&Ps.

thanks MoJo! That's good news. Hmm... I wonder if that holds true for my PX4 also...

Happy Thanksgiving!