Like I said earlier, what I remember about my Dad's AK in 5.56 is that the mag is much different than my X39 mags. I'm pretty sure they all use different openings in the stampings...I'd guess the shelf the front of the mags lock into are all the same since they are IIRC, part of the front trunnion, but I'm not sure there either.
"Necessity is the plea for every infringement of human liberty. It is the argument of tyrants; the creed of slaves."-William Pitt the Younger
Yup. Multi-caliber capability sounds good on paper, but probably not used/needed very often. Seen a lot of new for new-sake with ARs.
Fool-proofing serves only one purpose: identify bigger fools.