Bought a automotive 20gl parts washer to use for cleaning gun parts (do alot of C&R guns), trying to find what is the best solvent to use that won't damage finish on metal parts but will clean off oil/grease/cosmoline etc...
The cheapest mineral spirits you can find.
If you have an open area, I prefer white gas (Coleman Fuel) and a white 5 gallon bucket for small parts and short stocks.
I use an old vinyl eves trough with two end caps glued on for long stocks and actions.
2 gallons of Coleman fuel will lots of parts, and literally suck the cosmoline out of stocks if left submerged for 2-5 hours.
Here's a early Belgian FAL Stock that was literally black with cosmo that looked like this after a 3 hour soak and a light sanding, then boiled linseed oil hand rubbed finish with light 4 ought steel wool after each coat.....
unfortunately it's going in to my shop in the basement so it's has to be something that isn't flammable. Heard mixed results on the citrus degreaser (claims that it can damage blueing) but don't know how reliable the claims are.
Simple green works well if you have time to let the parts soak for a bit.
"Super" Agitene is the best parts washer cleaning solvent I have found. Removes Grease and Oil, Non Hazardous Formulation Includes Lanolin To Reduce Skin Irritation and Chapping.
Lanolin is also an excellent "old school" rust preventative.