I've been refinishing firearms for around 12 years now as a hobby.
I use a product called gun kote made by KG coatings. They recommend and I've used 120 grit aluminum oxide.
It apparently is the best media to use to prep for painting.
I was told by the owner of KG that it you looked at the surface of the metal under an electron microscope after blasting with glass beads or even silica sand it would look like a golf ball.
However with aluminum oxide the surface would be full of jagged marks which promotes much better adhesion.
I refinished a Winchester model 94 once using silica sand and when I was done the painting, baking process..I could peel the finish off with a finger nail.
I blast at 40 psi and at that pressure the aluminum oxide won't remove a gob of grease so I've never had any concerns with it removing metal.
It also helps keep the dust down and extends the life of the media.
Here is a Savage Model 99C I did a few years ago.
