The internet says the Pmag Gen M2 30 round mags left fully loaded will result in the feed lips spreading whereas a fully loaded Gen M2 mage fully loaded with dust cover will not be so affected.
As mentioned elsewhere, very recently, PMags don't work for me (for various reasons) except in my 7.5" pistol.
But where they work, mag 'bulge' and ejecting rounds haven't been an issue.
I have an assortment of G2 and G3 20s and 30s (half a dozen or more of each, from each generation).
Performance is basically the same.
If anything, the G3s have been less reliable. But, overall, that's with ARs that don't get along with PMags, anyway.