To follow up on my post #903, here are some more photos.
As mentioned earlier, the first batch of photos were from the owner.
These ones here are my photos of his rifles.
I took many photos but there is no point in duplicating the views already shown.
Hopefully these give some different insight.
This shows brass shim stock inserted behind the lug.
Each strip is .003" ("three thou") and it was easy enough to insert five pieces for a total of .015" or fifteen thou.
Similar test on left lug
Drill cuttings "swarf" that looks very recent.
One of the three guns had a bolt that was sanded/ground on the
side of the left lug.
Also notice the waviness in the area just behind. It looks as though it was given a light belt sanding, then sanded again at a slightly different angle or position.
This gives a distinct pattern when held in direct light.
Close-up of the rear of the right lug.
A couple of weld porosity holes are visible.
Also note the smooth shiny area and the area with straight parallel lines.
We suspect that the weldment is much softer than the ordnance alloy steel, and that the force of the proof round indented the soft lug area against the proper hardness receiver.
In this view, a gouge likely from a belt sander can be seen.
It carved a nick at the base of the lug.
In steel fab terms, this would be considered undercut and is bad because a crack could start there.
When "coping" a beam, it is poor practice to have a sharp corner as it causes stress risers.