Any place where there is metal to metal contact. Easy way to figure this out is to disassemble the pistol completely, coat all the metal surfaces with Dy Chem dye, reassemble and shoot a hundred rounds through it. Take it apart and any place where the Dy Chem has rubbed off needs to be polished. Seems like a lot of work, but if you want the same results as me, it's what has to be done. This is standard practice on any performance machine in many different disciplines. My background is auto racing so I brought this technique with me when I retired and started shooting.