From our perspective, it is simple. Our M&P recoil springs were designed for use in the full size pistols. These have a 4.25"� barrel. The SD40VE has a 4"� barrel and as such, significantly less room in the spring tunnel than the full size pistol. That explains the spring going to solid height. Not unlike taking a recoil spring for a 5"� 1911 pistol and putting it in a commander sized 1911. It just does not fit.

We have never sold these springs for use in anything other than the full size pistols or told anyone that they work in anything but the full sized M&P pistols. In more than 5 years, we have never had anyone contact us with a problem with spring performance when used in the full size pistols. For the SD40VE, I would believe that with the shorter slide it would need a recoil spring of a coil count similar to the Glock M19/23 size pistols.

Hope that this info is of some use.