I have recently bought a 357 Sig factory barrel for my M&P 40. I'm wanting to get a bit stiffer spring for shooting 357 Sigs. In searching the internet about spring poundage, there seems to be much information at odds with each other. Some say M&Ps in 9 & 40 are at 15 lb., and the 357 is 16 or 17 lb. Galloway says they're all at 17 lb. And Galloway's next step up is 20 lb. Brownells stated that S&W doesn't list a poundage for a replacement factory recoil spring. I'd like to know what other members here may have done or not done.