As far as using motor oil goes, has anyone tried Amsoil? I use their stuff in my vehicles, and it tends to maintain its viscosity across a wide range of temperatures compared to most other oils. It also doesn't thin out as much over time, especially with extended oil changes. I thought it might be good to use in guns. They actually sell firearm lubricants as well, but it's probably just the same stuff.
https://www.amsoil.com/reviews/firearm-cleaner-and-protectant-fcp/