Hello,
I have a m&p 2.0 4 in compact. I usually just shoot standard pressure everything, I however just happened upon about 200 rounds of 9mm Nato ( I understand them to be essentially +p) and a couple of boxes of 124 grn +p jhps. Do i need to get a heavier recoil spring? If so what weight?

I wouldn't, and didn't. The flat-wound ISMI springs that S&W puts in the M&Ps have a wider working range tolerance and a MUCH longer life span than the round piano-wire springs. I ran 6 seasons of practice and competition with the stock spring in an M&P Pro 9mm, and the spring was still fine when I changed it, just because I wanted to.

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