Its difficult to explain in words and my camera won't focus on the brass to show you all what I'm talking about. I have a G23 Gen 4. Here it goes. When looking at a casing after firing it, the primer has the typical dimple (inward) but its inside of a outward rectangle shape stamped or pressed during the firing cycle. All casings have the same post fire markings and no pre-firing marks. These markings occur with different ammo types (barrel 40 to 9 conversion). So it shows on 40 and 9mm brass casings. The rectangle shape embossment is the same shape and size as the open channel in the slide that holds the striker. The ammo is factory target with standard sammi loads. Various mfg's It may have been doing this all along but I just noticed last range session. On my other guns, this does not occur. Does my G23 Gen 4 have a issue? Thank You for reading my poor description. I tried.