The one trick I like for small rust "dots" is to use some gun oil and a older penny, say '70's when there was more actual copper content. Using the edge of the penny and a goodly amount of oil, "scrape" the rust off the gun steel. This will remove the rust and leave some copper in its place. Continue until smooth and wipe off all excess. the spot should almost completely disappear.
Fine steel wool and lots of oil also works, but can remove too much of the surrounding bluing if your not really careful.
Good luck,
CW