Curtis,
If you can find it locally, aluminum oxide powder will work better than baking soda. It's a little more abrasive and leaves a beautiful surface. It does require a respirator or good ventilation but works faster and gives good results.
I have an air brush sized blaster made by Paache, the airbrush people, that I use for small parts. It uses about 50 psi of pressure and does a great job cleaning and puts a nice finish on aluminum, steel, copper brass, any metal actually. I've used it to clean stuff and to etch glass.
I've tried soda but it takes longer and uses more of it than the aluminum oxide.
Just a suggestion. The idea for converting an air gun for a blaster is a good one however. Thanks for sharing.
Tom