The gun club I shoot at changed the rules this year to allow shooting pistol caliber carbines at most of the pistol ranges. Before that change I looked at them and decided a 6+ pound long gun that I could only shoot at the rifle ranges might as well be chambered for a real rifle cartridge. But being able to shoot one at steel plates or plinking type targets looks like a lot of fun. Kind of like a 10/22 on steroids.

I would rather not have to buy a new set of magazines which really narrows the selection. The only two I could find that take M&P magazines are the Just Right Carbine and Keltec Sub2000.

Any other carbines that take M&P mags out there?

Of the two I mentioned I would get the JRC. Once guns become available at regular prices again.

Google, man, google.
Finds this description of how to notch a M&P magazine to fit a Ruger PCC.

I don't see where that would keep it from still working in the pistol.

Stern Defense makes a drop-in 9mm conversion that takes M&P mags.

I’m not sure the point, tho, since there are no (reliable) M&P stick mags.

I have a 9mm carbine, and it’s a hoot. But it takes 33rd Glock mags.

I did see that but my past experience with third party magazines has been so poor at this point I only use factory magazines. I just would not trust a modified magazine. There is a big difference between locking into place and working reliably. Its not just whether they fit into the magwell and lock into place. It doesn't take much slop in the magwell or difference in feed lips to cause problems.

I often hear others talk about how well their aftermarket magazines or ones modified for greater capacity work. But with the exception of MagPul they have always been at best a little less than 100% reliable and often far worse when I try them.

Keltec Sub2000.

Where I would be shooting it even with a 17 round magazine I will probably run out of targets before I run out of ammo. The big sticks are fun but I would rather use magazines I already have.