There are several ways to refinish raw metal. Sounds like you are looking for a decent "do it yourself" method.
A sandblaster isn't the only way to clean a raw receiver. I'm sure that you have seen those "rust killers" around. Not the creamy type that supposedly turns rust into a primer, (if you believe that, I have some land here in Hawaii I'd like to sell you for cheap....) but the "Clear" liquid type like Jasco or SEM's "Rust Mort". All these products are is mild acid. The Acid cleans off any surface imperfections, and melts any porous rusted metal away to leave a clean almost blued piece of metal. The key to using these Acids is to apply it in layers, not just coating the flats with a coat or two, but to re-apply the stuff until is melts all the imperfections away. Put it this way, if you applied this stuff on galvanised steel the acid would literally melt all of the galvanise off!
Next, let it dry. It'll dry to a rough light blue colored texture. Instead of using water to clean off the stuff use alchohol...plain old rubbing alchohol. It dries super fast yet has enough solvents in it to clean off any surface grease. Then after all that;s done scuff off everything with a Green Scotch pad. This method cleans metal 100X better than sandpaper alone.
High Heat Engine paint works good as a finish as long as you bake it on. ***Try setting your receiver out in the Sun for a little bit before spraying it with the engine paint. Heat paint always adheires to warm metal than cold.
Catalized paints will always out perform spraycan stuff, no matter how expensive they are. Black Epoxy Primer creates a great looking finish (Semi gloss) and is as tough as nails as far as solvent resistance and durability is concerned. Epoxy also expands and retracts with the metal far better than non catalized paints can because of it's flexibility, and it will tenaciously hold on to bare metal even when the metal is sanded with 600 grit sandpaper. ***the 600 grit sandpaper does no scar the metal like a sanding wheel or scuff pad will resulting in a uniform SMOOTH surface.
Airbrushes are used mainly for art purposes and delivers material a little too slow and thin to be used to spray receivers. But if you must use an Airbrush, try to get a Single Stage one. It works just like a spraycan paint does: press the trigger and air/paint comes out. A 2 stage releases air when you press down, and fluid when you pull the trigger back. Instead of getting an Airbush I suggest you get yourself a CONVENTIONAL FEED touch up spray gun. Alot of companies will try to sell you an HVLP set-up (High Volume, Low Pressure) but don't get it. #1 it usually costs more and #2 HVLP guns take a LOT of CFM to work, so much so that a home compressor probably isn't enough to run the gun properly. CONVENTIONAL sprayguns are the way to go. Get yourself a regulated guage so you can control airpressure at the gun, and spray around 25-35lbs pressure.
If you have any more questions feel free to ask.