Still using the Navy Surplus "Oil, Light Lubricating" that I got years ago at 50 cents a gallon. If I ever run out of it I might try synthetic motor oil.

On the AR I use Slip 2000 because their hype seemed persuasive, but frankly I think anything slippery suffices. Back in WWII Melvin Johnson (of the Johnson Rifle) wrote a book, Practical Marksmanship, that had a very good chapter on the subject: "Put Oil On It". His advice was to keep guns running, use whatever you can get and put it where it needs to go. Made sense to me.

I couldn't keep track of all the brands of miracle oils if I wanted to.