I am also experimenting with modifying some M&P mags and CZ mags to implement during the carbine. You should cut the notch within the entrance of your mag so it will lock in. I don't very own any Glocks. I'd personally use Glock branded Publications and not the opposite copies. https://ruger-p89-for-sale56777.blog2freedom.com/32086185/rumored-buzz-on-ruger-p89-for-sale