For many years, my go-to product for rust prevention has been RIG, now available from Birchwood Casey, IIRC. Two things, both related to the fact that it is a grease and not a liquid: First, it can be difficult to get it into some tight places. Second, it is really easy to get too much on. The lightest, thinest coat that will cover is more than enough. By the way, treat the gun a few times with it, or use a dab on 4-0 steel wool, rubbed lightly over the surface will remove rust quite well. Just remember, nothing will fill in pits caused by rust.