Expert Review Works perfectly - Pro Mag AR-15 / M16 9MM Magazine Adapter Block For Colt 9mm SMG Magazines, Quick Change

I am running this in a 7" barrel pistol build, it went in well (just make sure it doesn't get caught on the mag catch during install) and comes out relatively easily. Magazines fit snugly but are smooth to engage and remove. However I would recommend avoiding the ProMag steel magazines, they required sanding due to the gritty coating on the magazine and failed to feed properly for the first 4 rounds every time. Swapped over to MetalForm magazines, and have not had a single issue since.