Help with AR upper manufacturer

[jsmann]

I recently purchased an AR-15 varmint/target rifle. The lower is a Rock River but the upper is unknown. The only identifying mark is a small raised (not stamped) insignia that resembles a key hole. I've pretty much ruled out RRA, DPMS, Bushmaster, and Armalite. Any ideas as to the manufacturer? - Thanks.

 

[alinwa]

Cerro Forge

 

[mike in co]

may i suggest you go to
ar15.com

and look around/ask there.

mike in co
(because while he is correct on who made the forging the upper was machined from, they did not make the upper assembly)