Sorry for not noticing this thread earlier too, with the Holidays it's tough trying to keep up with all the happenings at home let alone here too.
Any ways, I attempted for over an hour trying to get some decent pics of that wall area of mine and kind of gave up, but did get some of the chamber face area, I guess that's what I'll call it anyway. I did talk with Norm for a bit and we both think either a case didn't get extracted and got pinched by the slide and the mouth caused the impression, or possibly a stovepipe occurred and the ridge area caused it when trapped by the slide coming forward. All of mine seem to have some sort of a # stamped into that surface and a little bit of scarring of that edge too. Here's some pics of what I'm referring to. I'll post links to the higher resolution pics if you'd like to see those.
This first one is a 72 round hammer with unknown round count.
http://i210.photobucket.com/albums/bb25 ... C02319.jpg
This is my carry 74 w/500+rounds by me on right and a 75 that seems unissued with none fired by me on left.
http://i210.photobucket.com/albums/bb25 ... C02320.jpg
Next are two 72 round hammers, right has unknown rounds and left has approx. 250 rounds fired by me.
http://i210.photobucket.com/albums/bb25 ... C02321.jpg
Next left to right is 75 unissued, 74 carry, 72 w/approx.250, and 72 w/unknown round count.
http://i210.photobucket.com/albums/bb25 ... C02322.jpg
Last is same line up with a look of the wall in question.
http://i210.photobucket.com/albums/bb25 ... C02323.jpg
I'm going to post a link to this post in the other thread to kind of bring these together.