I'm currently using Mobile 1, 10W30. I use it on the all the exposed metal parts and use regular gun oil (mineral and synthetic) on the bore and internal parts. Motor oil seems to be working well for me. I just don't like the smell. Something about the smell of motor oil on my guns that doesn't sit well, but I get over it. Synthetic motor oil is relatively inexpensive, especially when compared to gun oil, and it has superior qualities.
I've used it on cases but didn't really like it. Seemed too thick or something. I tended to dent the cases easier when using it. Went back to Hornady and Lee lubes, at least for now.