CPD has both 28 and 30 round mags for 7.62x39. The 30 round is a "Gen III" but is cheaper than the 28. Any performance difference between the two? Anything I should avoid? Thanks,

i thought, perhaps mistakenly, that they weren't shipping the 28-rd versions anymore?  i.e. discontinued?

i had back-ordered some of the 28rd versions from Brownells a few months ago, when the order was finally fulfilled, what arrived was the 30rd versions.  i'm not complaining, they work fine.

I ordered mostly 20s since I like to shoot prone or bench and hunt. I got a cpl 28s since they fit in mag pouches unlike the 30s.  Just don't get the old gen 28s which were 30s that didn't fit all the rounds due to geometry/follower.  They redesigned/improved the old 28 to hold 30 and then made a slightly smaller version of that improved mag to fit in 5.56 mag pouches which is the new 28.