I haven't done a thorough look online, but is there a reliable source for these mags with the center notch on the front face of the magazine? All I seem to come across are the regular Gen4 double-corner notch magazines, both from retail and in distribution. Looking for these on behalf of a buddy who now owns one of the limited Gen3 ambidextrous mag release SF models, though his doesn't have the Picatinny rail. Previously I'd never seen one so configured before; the few SFs with ambi mag buttons I'd previously encountered have had the full equipment rail.

These are good quality aftermarket mags that are configured for both types of mag releases. I have one of those G21's as well.

https://www.cheaperthandirt.ne...refType=&from=Search

All of the G21 magazines I bought last year had the center cut out and the notches on both sides. They would work in any of the various magazine release setups. I kind of assumed that was Glock's new standard.

All G21 Gen4 factory magazines have the center cut for the ambi mag catch.