Does anyone out there know how to identify what brand upper receiver you have. Like in the manufactures stampings and location of the stampings on the receiver? I bought a used receiver (was told it was a DPMS) but not sure how to prove it is.

There are four to five forging contactors that produce the upper receivers. All the AR manufacturer's buy their raw forgings from these contractors, and then do the detail and finish work themselves. So the forging marks will only identify the contractor, and not the "brand".
In the last 6 months, I have seen Bushmaster, DPMS, and Oly upper receivers and Bushmaster, Colt, and "JT Distributing" removable carry handles, all with the [url=fogings.com]Anchor Harvey[/url] "splintered A" forging mark.

My postban upper bushy has an ordnance bomb stamped where the letter designation would be any idea who made that one?

I checked my upper and it does have the0 " splintered A" cast into the forging just in front of the rear sight. So I can only assume that it's a DPMS.

One of my Original Pre Ban Bushmaster's have the letters D/A on the upper !!!

My DPMS upper is marked FK.