Simple Upper Question
 

This is going to be easy to answer. Just what is a Keyhole upper? What makes it different from another or is there a difference? I just see it mentioned on occasion and was curious.

Cerro Forge did the forging I think....could be wrong.

you are correct. cerro forge is a major supplier to many vendors who just stamp their mark on someone else's work.

very few makers will tell you where they get their pieces from. there is a distinct difference between an ar assembler like red jacket and a company that rolls their own recievers.

Yep, Cerro Forge and they put their keyhole forge mark on uppers, lowers and carry handles used by Colt and many others.