Jim,
To add to your list of advantageous properties of synthetic motor oils, I've read that a significant advantage is the ability to flow well at temperatures below normal engine operating temps (startup). Contrary to popular belief, thin oil works better in engines.
I think that is working against you for gun hinge use as there's no oil replenishment system when the oil flows out of the hinge.
Chuck:
I've always been a grease adherent for hinge pins and have been using it for over 40 years. I can not detect any wear whatsover to the pins or hooks on my doubles.
I suspect there are other approaches/products that will work equally well but I've also always been a subscriber to "If it ain't broke don't fix it".
Jim
