AR Upper Receiver Basics?

[LRRPF52]

LRRPF52, I had a feeling you'd know, good stuff thank you.

You just don't know where you're going until you figure out where you came from.

Wait 'til you see the variations in original AR10 uppers, between the Armalites made in Hollywood CA, the Dutch, the Portuguese, and Sudanese. The original AR10's were a work of art, and probably the only mass-produced battle rifle that was controllable in 7.62x51 NATO...a beautiful weapon really.