Nonsense. 40 round pmags for the AR have never failed me.
Neither have 33 round Glock magazines.
Nor 50 round PS90 magazines.
Why do you talk nonsense?
Matt Bracken on “duplexed” AR mags:
https://westernrifleshooters.blogspot.com/2010/09/bracken-in-praise-of-duplexed-ar-mags.html