Dimensional info question

[Grendel Guy]

I was hoping someone here could give me the nominal dimensions for size and location of the radius @ the rear of a .308 DPMS pattern upper receiver (nearest the receiver extenstion hole). I bought a lower (80% initially but now complete) and an upper 100 %)from two different manufactures. The one who made the upper won't pass the info, says it's proprietary, but can be found somewhere. The two won't pin together and seems the interference is with the two radii. Thanks in advance