I bought a M&P 40 with a 5" barrel. When I went to the gunstore to buy it, I told them about this thread. They took out a M&P 9 with a 5" barrel and installed the barrel into a M&P 40 with same length slide. Every time they racked the slide back the barrel wedged itself into the slide and kept the slide from returning to battery. This happened at least 5 times & then they announced to me that it does not work.

I ended up spending $150 dollars on a Storm Lake conversion barrel because they told me that the 9mm 5" barrel didn't fit into the M&P 40 (5" barrel) at the store. They wouldn't let me try it myself because they said that I might break the gun & they would rather that they be held liable for any damages instead of me. Did I get lied to by the store employees in the hopes that I would buy a 9mm M&P from them instead of ordering a barrel on the internet? Is the 5" barrel so different from the 4" barrels that you can't swap out 5" barrels but you can swap out 4" barrels?

I guess I need to hear from some one who has swapped out 5" 9mm & 40s&w barrels with success...or failure. Anyway, the storm lake conversion barrel I bought has been perfect in my M&P 40. It shoots at least as accurate as the OEM barrel & I have not experienced any FTF's of any kind. So maybe I spent approximately $50-$100 more than I needed to, but at least it performs and isn't junk. But then again, blowing $100 in this great depression causes great depression. OK peoples, talk to me...

...Upon further reflection, I do know that I can't make my conversion barrel wedge itself in the slide like the 9mm barrel did at the store. There isn't that much play in the slide that would allow the barrel to travel within the slide like it did when the employees were trying it. There was something amiss in that experiment which allowed for that barrel to be able to travel back and wedge itself in the slide...