These guns are made of wear resistant stainless steel specifically 410 alloy stainless. This stuff is known as a martensitic stainless steel. These alloys are unique among stainless steels as they can be hardened by heat treating and possess properties that make them very useful for firearms manufacture as well as other "high wear" applications. These steels are also slightly magnetic and are not quite as corrosion resistant as you might think. In other words, they will rust.
So, how do you make scuzzy old guns made from this stuff pretty again?......
Here's what I do...
First I detail strip the gun as in completely disassemble. Then I take all the stainless bits (slide, receiver, & barrel) to the kitchen sink and with some Dawn or Simple Green and and a old toothbrush, scrub away all the crud. Safety Note: strong degreasers will also strip all the natural oils out of your skin, nytril shop gloves will protect your hide. Pipe cleaners and wood toothpicks are useful for cleaning out small holes. Avoid using any wire brushes as steel wire will scratch stuff and brass/bronze wire will embed in and discolor the surface you're trying to clean.
Most of the time all that nastyness and staining is merely a buildup of old dried or burned lubricant + powder residue + carbon scale and will clean right up with a good degreasing agent and a little elbow grease. Often times you'll find after pulling your parts out of the sink and drying them off that everything looks fine now. Might as well slap the thing back together and head to the range
However, once you get all the crud cleaned up there may still be some rust or rust staining. A mild acid will clean this up. White vinegar (acetic acid) serves perfectly. I'll soak the rusty parts in a glass dish of white vinegar for as long as it takes to eat the rust away. Some will clean up in an hour and some may take longer. I'll pull the part every hour or so, wash it off and check it out. If there's still some rust it goes back in the pan. Rinse and repeat until you're satisfied with the result. And... be sure to use a glass container. You want to be sure your container is non-reactive so I use a cheap Anchor Hocking baking dish from Walmart.
Now all the rust has been cleaned up there may be some pitting, dings, or scratches to deal with.
If there is some deep pitting from heavy rust there may not be anything you can do about it. Severe pitting can be repaired but it requires micro welding with special equipment then re-machine or file the part back to original profile and re-finish by blasting.
Now a blast cabinet or a small handheld sandblaster is quite handy. You can literally erase small scratches and dings using the proper media.
About blasting media...
There are many different types of blasting media each with different properties for certain applications. In the firearms industry you'll typically see these two: Glass beads and Aluminum Oxide. And each of these can be had in a variety of grit or mesh.
The main difference is glass beads shatter on impact and wont remove any metal or change the surface profile whereas aluminum oxide abrasive media will.
Say for example you have a gun that's just scuzzy and has some light burnishing from holster wear. Glass beads would be the right media here to brighten up the finish, clean up & restore the appearance of the factory matt finish over any burnished areas while NOT change the profile or texture of the original factory blasted finish.
Conversely, say you have a gun that someone had mirror polished and you'd like to restore the factory matt finish. Glass beads here would only make it slightly non-shiny. You need media with more "tooth" to raise the surface profile or texture and roughen up the steel to match the original factory finish. This is where aluminum oxide shines. Aluminum oxide is actually synthetic rubies and second in mineral hardness next to diamonds. It will abrade away the steel to some degree depending on what grit is used. This property is exactly what makes that nice slightly rough uniform matt finish we get from the factory.
I have a small blast cabinet I got from Tractor Supply filled with 270+ glass beads I got from Brownells. This pretty much meets my needs for cleaning up old beaters so far. If I decide I need something more I'll probably set up second little cabinet filled with aluminum oxide media.
You may ask... Why not skip all that washing and scrubbing, dipping and soaking and go right to the blasting to clean up this scuzzy gun. Well, the reason you don't want to do that is you do not want all that goo contaminating your media. Anything you put in the blast cabinet should be clean free of goo and especially dry. Any gunk or moisture that gets in there will cause your media to clump and stop feeding through the nozzle. You'll wind up having the clean out the cabinet and replace the media which is not a job you want to do very often.
In any event when messing with any abrasive blasting equipment, make sure to protect yourself. A quality respirator and goggles are mandatory at a minimum. The dust generated inside a blast cabinet or in open air blasting is very hazardous and something you do not want to aspirate. Google "silicosis" if you're curious.
Information overload huh? Ya I tend to do that at times.
Anyway, that's how I get it done. I Hope you find some of this useful.
Cheers
Bill
) Well as it turned out, I took something with no collector value and turned it into something very nice & unique that I carry regularly. The point being, I quite understand your trepidation in tackling a blasting/refinishing project. 
