Raimey,
The early 9.3 ammo was primed with the M71 6.45mm (.254") primers and we often see a circle around the firing pin that looks like the "reinforcement" you observed, caused by corrosive gas leakage around the large primers. Early 8.15x46Rs also used these primers and often show the same circle, as do rifles chambered for 11.15x60 R or other cartridges based on that case.
Mike