Dimpled Receiver?

I've never seen a dimple on the rear of a receiver, but I wonder - is there raised metal around the circumference of the "crater?"

If so, I'm reminded of an article in CC NL 335-10, where STD PRO's Ellis Lenz reported "poor fit of the recoil plate to the rear of the receiver" affecting the consistency of carbine accuracy. That dimple could be an attempt to tighten up that fit.

Decades ago, I used a punch to "crater" a recoil plate to tighten the fit, but results were inconclusive. In hindsight, my "craters" weren't deep enough - didn't raise sufficient metal to tighten the fit.   Another collector actually cracked a recoil plate doing this, but I don't remember if it was a milled or a postwar cast recoil plate.

Another shooter used a portion of a matchbook cover between the recoil plate and the recoil lug of the receiver to tighten the fit.

Because I was shooting in the Carbine Matches at Camp Perry, I didn't want to violate the "as issued" requirement for eligible carbines, so I purchased a handful of recoil plates and used the one that had the tightest fit...although the "lock up" wasn't as tight as I would've preferred....Is that a good excuse for a poor score? :-)

Regards, mb

Here is another view, looks like a larger than "punch" size dimple. I do not believe it was intentionally done to tighten the recoil plate/receiver fit.

For reference, it is a SG subcontracted Inland receiver.  The dimple is very shallow and perfectly centered. 

Thinking like a Ham handed Smith or Bubba dealing with a tight fitting or stuck Trigger Housing.

is it just the lighting or is there finish down in the bottom of that dimple? If the carbine retains its original finish, then that would suggest the mark was made early rather than a bubba. But if it's been refinished who knows. If we can determine if the carbine has its original finish, that would at least give us an idea of when the odd mark was put on there. I could be wrong but I would suspect if it's original finish and is present in the bottom of that dimple, then the dimple would be from some kind of anomaly from the manufacturing process

well dogdoc, I'm definitely no expert, I'm just throwing my thoughts out there. we will have to wait till the experts can verify your finish is in fact original. Even if it is, I may still be wrong haha