I've had success with some Mothers Metal Polish and a bunch of elbow grease. Just keep rubbing until you're blue in the face. I was also having a slight delay in chambering with certain brands of ammo when my gun was brand new. After polishing and over a 1000 rounds later, I've never seen...
I drove there from Flowery Branch to buy my last pistol. Worth the trip for sure. Very kind and helpful people there. Never had someone break down every weapon in the category I am interested in and lay the parts out in front of me. Then go on to explain all the advantages and disadvantages...