My Storm Lake 9mm conversion barrel came today. Put a box through it in the backyard on steel and it was lights out. I'll rest it and shoot paper to check the POI, but I could hit a 3" spinner target from 15 yards as effectively as I can any of my other 9mms so its going to be pretty close most likely.
As far as using a stock 9mm barrel, I read up on this for a while and just could not get myself to do it. The lockup part of the barrel is not as thick from stock 9mm to stock .40. The conversion barrel is thicker in this part to where it fills up that gap. I've seen people on forums using them, but for what I'd save between them, I chose to just go with the actual conversion. Zero problems in my Storm Lake .357 and 9mm barrels, and no more regrets about buying the FS 40 nowdays. Its just a 3 in 1.