I have a glock 23. I took it to the shooting range about a week ago. I noticed brass shavings on the slide when I removed it. Is that normal. This is my first pistol but not the first time firing one.

OK..I have a Gen 3 model 23 and just purchased and Gen 4 Model 22. I upgraded my Guide and spring in the Gen 3 and Installed a Buffer. Has anyone upgrded their Gen 4? Also comparing the 2, aside from the Guide and Spring assemble, is a courios little bump on the trigger slide mechanism. Does anyone know why that was done?