I use thin oil for cleaning, like wd40 or crc5-56. For lubricating and preserving I use car motor oil , Mobil Rally Formula 5w50. As a fully synthetic oil it works great even in -27C temperatures( this I have tested) in my ar-15 and MP15-22, too. And in hot weathers like 30C it still looks oil after day in range . It don't evaporate.....as CLP and some 'gun oils' does.
Course motor oil comes 'black' in ar-15 bolt and carrier, but it only means that oil collects dirty off from mechanism and there is not any carded.
Sorry about this C-mark ( Celsius). I don't have any understanding about 'F'. All free world exept english spoken countries use C, m, L and G, which are internationally agreed measures, even by US. But still we here in Europe have troubles to find tools and bolts for 'inch'-seizes.