The 29rd., G22 and G23 mags will all work in your G27. There is an aftermarket sleeve that is available for use with the G22 mags. It fills the gap with the longer mag. I use them when shooting my G30 with high-cap G21 mags. It can be purchased on many Glock accessory websites like http://www.lonewolfdist.com/ You can also purchase +1 extension for the 9 round G27 mags to bring total capacity to 10+1. It also offers a place for your pinky finger on the grip.