Details
M&P 2.0 4.0" models can use either a "flat" spring like this ISMI spring or a "round" spring like the Wolff spring. If using a captured guiderod, we recommend the use of a "flat" spring like this ISMI spring. These springs are excellent springs and can be used for all types of shooting.
The ISMI can also be used with an uncaptured guiderod as well. Be sure that your guiderod was made for an ISMI recoil spring. The Wolff spring has a larger inner diameter.