5.56 Ammo

What is the difference between 5.56, 5.56R and 5.56 NATO? Or is it all the same?

Never heard of a 5.56r

Is that a model or a caliber?

Your standard 5.56 and 5.56 NATO are the same thing.

Buy a 223 Wylde it'll take .223&5.56.

This is a good explanation:
https://www.youtube.com/watch?v=VCS4fXFmCyA

5.56R perhaps actually 5.56x39 Russian?

5.45x39mm is superior.

The 556R is a Sig model number, not a caliber. It's a 7.62x39 which accepts the AK magazine.