WD40
Have used WD40 on my collection for at least 20 years. Blued, parkerized, stainless, nickle - no damage of any kind. I saturate the gun, blow it out, wipe it off, swab the barrel, and use Hoppes #9 oil for lubrication on all points of friction and metal surfaces. Rust is not an issue and crystalization is not present. Some guns have been totally dismantled and inspected. I shoot approximately 10k rounds total per year through 16 pistols, 2 shotguns, and 6 rifles.
Best to you.