I have a couple of questions that I've been getting mixed results. I have a S&W M&P 40 that i would like to be able to convert to 357 Sig. 1) I know that Barrel needs to be changed and S&W and Storm Lake have conversion barrels. Are there any other manufacturers? Im more familiar with Glocks. 2) The mags are interchangeable but does the recoil spring need to be changed? Now if I want to change my M&P 40 to a 9mm. I get differing results from gun buddies. Some say they have read that the 9mm conversion barrel can be put in the M&P40 but not the other way around 40 into a 9mm. Others say I would some gunsmith work due to the ramp feed. I really dont want to invest in a 9mm conversion if I cant convert back to a 40 or 357. I saw that Storm Lake has a conversion barrel but is it worth it? If so then I would have to buy some 9mm mags then I would have the ability to have 3 calibers with one gun. Thats the goal for right now. I tried to do a search for conversions but not specifically for a M&P 40 to 357 Sig or 9mm Thanks for your time.