I have used moly grease for years - Birchwood Casey. Works fine, but that is for shooting above -10F.
Before switching to the moly, I used synthetic bearing grease by Amsoil when hunting down to -40F (one late fall, -56F)
That was cold weather hunting that breaks main springs. I wouldn't advise it. We stopped shooting our trail at -20F, due to that problem.
Amsoil's 85/90 weight gear oil, pours at -40F, BTW. It would also work well as a lock lube, all year - just a 'touch'.
Most motor oils today are either partial synthetic or 100% synthetic, whether they say so or not. A 100% petroleum oil
today is just about impossible to find.
I've read with petroleum oils, temperatures today would be over 300F in the bearing races, and that temp turns 100% petroleum
oils into asphalt.