The kit that I'm looking at isn't just one of the drop in barrels you can buy to go from .40 S&W to .357 Sig. It includes a new slide as well as the barrel and a few other parts. Here is the link for it.
http://www.midwayusa.com/product/153...round-magazine
On Sig's website it says its made to switch a .22lr P226 to one of the centerfire cartridges. I'm just wondering if the kit will work on a 9mm frame or if there is a difference between it and the .22lr version. MidwayUSA doesn't mention it being specifically for changing a .22lr but Sig's website does.