The term "mineral oil" has a usage referring to oil from geological sources as opposed to plant and animal sourced "oils".
See:
http://en.wikipedia.org/wiki/Mineral_oilBased on reading years ago related to knives, I have been using "mineral oil USP" (United States Pharmacopeia) as a lubricant for years. That's another common use of term - specifically meaning the drugstore product. I've also seen it referred to as "FGMO" food grade mineral oil.
It's cheap, clear, non-toxic, non-oxidizing, won't go rancid, and is a pure grade without additives. Available at any drugstore. I put it in a little squeeze bottle with a needle adapter and use it for many purposes.
I think that chemically, it is almost the same as ND30 oil, but It has a better purity. I apply it to my maple cutting board occasionally, and it is sometimes used as a finish for wood.
That being said, it has a flash point, and it's flammable. I think one should be careful using it in airguns, as it would certainly diesel if it gets in the wrong place.