Its a key hole marking, who made it ?
And is it a good upper receiver ?

No way to tell. The keyhole is the mark of the forge that turned out the raw blank, and all the major aftermarket manufacturers are using blanks by the same 2 or 3 forges.

This is what I learned from a previous post:


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Quoted:
The upper reciever forgings with the keyhole with two dots inside is manufactured by Cerro Metal Products. I was talking to one of their Rep's the other day and I asked what the symbol stood for. This is what I was told (as close as I can remember anyway). The first dot represents the customer the other dot represents Cerro. They are enclosed in a key hole because their relationship is the "key to their success".
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Thanks for that info, its been a popular question lately.
Cerro Fabricated