If they use Beta mags with the IAR, we'll merely be transitioning from the JamMaster 5000 to the JamMaster 5000 Mod1.
As stated, Beta mags have reliability issues. Strike that, they have significant reliability issues. Even when somebody sends one back to the manufacturer to get reworked, they come back, do okay for a while, then find a new way to create feed problems.
Plus, they're an even more awkward shape than a SAW drum.
Plus, they take up a much more awkward amount of real estate on a vest.
Plus, they weight more empty than a SAW drum does. Part of the idea is to try to lighten the AR gunner's load, or at least make it easier to handle.
Plus, they look stupid. Everybody knows: if you're gonna screw up, it's okay as long as you look good doing it (this is why sunglasses are so very, very important :D). They're not reliable enough to look as dumb as they do.
They are/were being tested, but the likelihood they'll become issue gear is on a par with that of me being elected Pope. Only folks that like those things are the ones that took the movie 3000 Miles to Graceland to be a documentary film, and fortunately they're noit part of the source-selection process (though sometimes I wonder...).
The 40rnd widebodies look promising, as does the 75rnd drum Dano mentioned. Much more sensible for the platform, but only time will tell if that's the way things will go. We all will just have to wait.

