600 grit sandpaper
1000 (or finer) grit sandpaper
Dremel tool or equivalent.
Felt wheel attachment
Automotive rubbing or polishing compound.
1) Remove the slide. If you can remove the barrel, do that too.
2) Using the 600 grit, lightly smooth the feed ramp. Also, remove any rough edges around the chamber, taking care not to bevel it. You want to SMOOTH the metal, not REMOVE it. Do as LITTLE as possible in order not to change the geometry of the chamber or feed ramp.
3) Repeat with the 1000 grit. This should take out the tiny scratches that the 600 grit left behind.
4) Now, take the Dremel with the felt wheel attachment. Coat lightly with the polishing compound. Be careful to hold this away from your face when you start it, else it may sling compound in your eyes.
5) Polish the ramp, if possible by moving UP and DOWN the ramp. Do this until you have a chrome-like finish.
6) Wipe and clean thoroughly, being sure to remove any polish residue. If necessary, swab the bore as well.
7) Your feed ramp should be nice and shiny and look like this:
8) Reassemble your gun. Go test it out.