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Thoughts on 40 to 9 conversion kit


Bill Schwab

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I'm about to purchase a 5" M&P 40 Pro and saw that KKM sells a 40 to 9 barrel. Seems like a neat idea, but I'm concerned that the 40 breechface, extractor and heavier recoil spring may cause malfs. Anyone have experience with one of these conversion barrels?

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Sort of. One of the members here offered me a factory 9mm 5 inch barrel to give the conversion a try. Worked slick. I think all of those parts you are worried about are the same for 9mm as .40. There were several threads when I researched it. Someone posted the part numbers for the parts at Brownell's were the same for both as I recall. Course I can't remember what I had for lunch and YMMV.

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I considered doing the conversion on mine, but since I'm standardized on .40 in other divisions I decided to just load .40 Minor vs. buying a barrel, mags, dies, etc.

If you're already set up to reload 9mm, or don't reload at all, then I guess the conversion is the way to go. Good luck!

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The Storm Lake and KKM conversions shoot GREAT in the 40Cal M&Ps. A STOCK 9mm barrel will FUNCTION in a 40 slide, but is not accurate or safe due to size differences in the locking block and barrel lugs.

Of course you cannot shoot your 40-9 conversion in Production, since rules mandate same caliber barrel-swaps only.

You'll also need 9mm factory mags.

Jeff

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I have a 5" KKM 40-9 barrel in my 40 pro. It shoots well, POA/POI is pretty close to the OEM .40 barrel. it's a mirror finish on the inside compared to the stock barrels rougher looking texture.

I haven't done anything to the extractor/ejector and the only time I have had an issue was with underpowered reloads usi g TrailBoss (3.1 grains with 180 gr bear creek works well for .40 minor!)

I think my max OAL with 124 gr Montana Gold JHP is 1.150"

No feeding issues either.

I've fired 95, 100, 115, 124, and 130 gr rounds all flawlessly. Haven't tried 147 grain rounds yet.

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I've got the Storm Lake 40 to 9 conversion bbl in a M&P FS. I got it in case there was ever a problem getting 40 ammo for HD. It turns out it is totally reliable and more accurate than my buddy's factory M&P 9mm. POA/POI between 40/9 is a wash. No changes except putting in one bbl or the other and using the appropriate magazines. Highly recommended.

John

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Well, I probably should'a tried the 9mm KKM barrel from my 9L before I bought the conversion for my 40 Pro...but too late now. I just got it today, put on my TF +6 9mm extensions and springs, and I'm off to the range. Wish me luck! :unsure:

Edited by rack&roll
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  • 4 weeks later...

The KKM .40 to 9mm M&P Pro conversion barrel works great, and very accurate. I've shot 2 mini-matches with it and probably 300 rds practice with no malfunctions. All I could ask for...highly recommended. :)

Edited by rack&roll
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