Anyone seen this on back of Receiver?

[painter777]

Jim,
I first mentioned maybe a high spot was knocked down that impeded a good Recoil Plate fit, but they shot that down.

Hardness test has been brought up, but no follow up yet. Just such a strange area to test IMO.

I have no idea, never seen or heard of this before. It's being knocked around on the CCCF.
I tossed out a WAG today that maybe the Trigger Housing was stuck and Bubba took a Hammer or Housing pin and knocked it with a Ball Peen to loosen it ??
Using a Pin or Punch to get above the top edge of the Tang.
But IDK

I think it was the owner who stated:
"For reference, it is a SG subcontracted Inland receiver. The dimple is very shallow and perfectly centered."

[browningautorifle]

Hardness test has been brought up, but no follow up yet.

Just because when I was a Platoon Sgt and while examining our rifles, I found my Officer's rifle had a Mounted Police marking and some Rockwell markings, tests. The rifle was an even number so it had been selected, like a number ending in 50. I don't recall seeing it before or since. It was of course the FN C1 A1 rifles, way back early '80's.