Couldn't it just be that everything was done right at the factory, but it's so tight that firing it causes the finish wear in the pin holes (there is almost no play between the upper and lower on mine)? I was told it was normal. My only concern is whether it will cause the receiver to have less service life. It’s present in the lower on mine.
ETA: I never noticed the finish wear in my pin holes until after I had about 1000 rounds through it. Not sure if I just hadn’t noticed it before then or if it was part of the break in.
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