It is going to vary enough from gun to gun that you can't really rely on other people's results.
Furthermore, the difference in accuracy between, say, Brand-A 155gr JHP and Brand-B 180gr JHP is probably insignificant compared to your skill level, so finding the load that you shoot best is going to matter more than finding one that other people say shoots accurately.
You'd need to know what bullet weight/velocity Smith used for that particular gun when it was tested and sighted in. I'm not trying to make this hard on you, but if you ask 20 M&P40 owners you'll get 20 different answers. Why? Because their reported accuracy will depend so much on their shooting skill, their chosen sight picture technique, how a particular gun/barrel reacts to a particular bullet, etc.
Example: my carry ammo (124gr @ 1,220fps) shoots exactly to POA at 25yd. IF I use the white dot of my front sight as my aiming point. Which I just happen to do.
Example: my practice ammo (115gr @ 1,145fps) shoots exactly to POA at 25yd. IF I use the top edge of my front sight as my aiming point. Which I don't do, so instead I know my shots are going to land about 2" high at that distance.
Odds are that any standard weight bullet will be close enough to your POA that the differences will still fall well within your wobble zone.
I'd have to say that although the M&P series is plenty accurate enough for a duty/defensive pistol, its not really a tack driver. Almost any of the high-quality hollowpoint loads out there will be accurate enough for social work, while likewise none of them are going to win you any Olympic medals for bullseye shooting.
Do a search for DocGKR's recommendations on .40 carry loads and you can't go too wrong. You may also want to check out the short barrel Gold Dot loads from Speer, as I understand they are optimized for use in weapons with a 3.5 inch barrel (which happens to be exactly the barrel length of the M&P40c).
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