If your M&P is the fullsize (4.25 inch barrel) then you need the fullsize mags. Some places may not specify since 17 round mags are full size. There are reduced capacity mags (15 and 10 round) for restricted states but those just about always specify. You slide should read M&P 9 up by the front sight.

The M&P9 Compact says M&P 9c up by the sight. These too generally specify Compact. Full size mags will fit the compact, just stick out a bit more. Compact mags will not fit the full size.

Finally, the Shield will also say so up by the sight. Shield mags will not fit the full or compact.

Here are the three of them all together.



(and yes, there are FOUR lights!!)