Works perfectly with s&w m&p mags - Stern Defense MAG-ADMP9&40/P320 AR-15 M&P 9mm/.40 Magazine Conversion Adapter

I like to pair my pistols with a carbine that accepts the same mags. I could have bought a Response or FPC from Smith or a Sub-2000 from Kel-Tec (I have one, it's nice) but I had parts that included a AR-9 barreled upper and a AR lower. Talk about a perfect match. It went in easy and setting it up (the three set screws) was quick. After one trip to the range it has been flawless. It stayed secure and no issues with mags, feeding or ejecting. If you have an M&P in 9mm or .40 S&W this may be a way to add a long gun that shares mags, ammo and keeps the recoil down.