G.41 duv43 - odd receiver hole

Cyrano4747 said:
Are you talking about the chatter marks between the flat where the model info is stamped and the rear sight?
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Yes, but I don't believe it's chatter. Why are these marks only on the left side? As biggymu asked, why are they not going lengthwise like all the other machining marks? They look like something you would find on the slide of a pistol but they serve no purpose here.
There is not a lot of room behind the hole because this is where the big end of the op rod disappears into the receiver during recoil.
 
I am not a machinist but I understand machining processes. Difficult to imagine a period tool that could produce this pattern in such a complex surface vertically. Perhaps the forging process left this behind and it was supposed to be sanded? Weird. The hole is much less interesting.

The rear sight rivet has been disturbed also on the opposite side.
 
Here are about the best pictures I can take. Very intriguing both the hole and the machining pattern. Funny how I picked this up long, long ago just for spare parts. IMG_1774.jpegIMG_1776.jpegIMG_1777.jpegIMG_1778.jpegIMG_1779.jpegIMG_1781.jpegIMG_1782.jpeg
 
The WaA 214 sits high on the flat and goes into those tooling marks. It's clearly sitting over them. Whatever those marks are they were put on before the WaA was stamped. My guess is that the marks ran the full way down the side of the receiver before they made the flat for the markings.

I don't know what kind of milling was done on these, but I'm still leaning chatter or something similar. You can get pretty regularly spaced marks that way.
 
Cyrano4747 said:
The WaA 214 sits high on the flat and goes into those tooling marks. It's clearly sitting over them. Whatever those marks are they were put on before the WaA was stamped. My guess is that the marks ran the full way down the side of the receiver before they made the flat for the markings.

I don't know what kind of milling was done on these, but I'm still leaning chatter or something similar. You can get pretty regularly spaced marks that way.
Click to expand...
Yes the new photos show better detail. Looks like marks left by a rotating cutter created as it was fed incrementally along. For whatever reason it was not finished.
 
The chatter marks looks like the milling machine was set with work feeding too fast into a cutter that was dull and/or rotating too slowly. My guess is that this was done in a horizontal mill with a custom profile shell cutter.
 
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