1. Take gun apart.
2. Wet all parts with a good penetrating oil.
3. Let set for 24 hrs
4. While waiting beat the idiot that did that with a ball bat
5. Use a Chore-Boy COPPER pot scrubber. Wet it with same oil, rub gently by hand.
6. Gun will turn coppery color. Wet with some MORE oil, rub with clean soft cloth (color comes off)
Blueing is probably shot. Above will make it look BETTER, but only a reblue would make it look GOOD.
Repeat step 4 as needed. Best penetrating oil made is KROIL, made by Kano labs. Google is your friend.