Fast Fact #1
Full size M&P's, 9mm, 40 S&W and 357 Sig all use the same frame, so no, the 357 Sig won't batter the frame. I'm pretty sure you are using a 357 Sig barrel from a known manufacturer, and not from some guy on the corner who sold you a barrel with no markings out of his trunk, so I wouldn't worry about over pressure as long as you are using the proper ammo.
I'm not sure if the 357 Sig uses the same recoil spring as the 9mm or 40 S&W which both use the same recoil spring.
HEY!!!! wow im impressed, you guys are really great! thank you soooo much for all the info! im so excited, haven't pumped any .357 sig out of my new .357 sig barrel from the S&W factory, you guys crushed my doubt! thank you and i look forward to many good conversations in this wonderful world of M&P
From the factory, the M&P357 had a 17 lb. recoil, as did the M&P40 for the first year or so. They no longer make the heavier recoil assembly (I think it was painted green), since they discontinued the M&P357. The current recoil assembly, with it's 15 lb. spring, ships with every f/s model of the M&P, and is available from the factory (often just for the asking).
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