Well, out of a whole bunch of pictures taken very awkwardly, only one came out remotely clear enough. This is the breechface of my P-10C 1st gen, which has several thousand rounds through it. At first glance it looked like yours, but it hasn't been cleaned in several hundred rounds. A few passes with the GI toothbrush and Weapon Shield gave me this;
I think what you have is the normal cut out with an accretion of carbon buildup. Scrub that puppy clean, but even filthy, it won't affect your pistol.