I finally got my M&P .40 Compact converted to 9mm, using the Storm Lake barrel. I'd previously bought one for my M&P 40 Pro CORE.

The barrel was an easy drop-in conversion. I only needed to buy a 9mm magazine to start testing.

I took both guns to the range today, and ran 200 rounds through them. I put 50 downrange for the CORE, and 150 to break in the Compact. The CORE continues to run like the proverbial singer; no failures of any type.

The Compact ran Winchester white box, Federal, and Rem/UMC flawlessly. No FTF's or FTE's. The recoil on the compact is just a tad less snappy than the .40.

I don't know that the Compact will be carried as a 9mm, but they sure are a lot of fun shooting.

Good luck with your set up. I have the CORE in 40 and a KKM 9mm barrel for it. The gun runs great.