Yeah, it's one of those "D'oh!" moments. We all have them.
I have turned around for ammunition a few times. About ten years ago, I took a 303 Epps with me moose hunting. 30 miles from the house I turned around. Several times when heading to the range. I always take two rifles with me when I go hunting, Just in case something happens to one of them.
Once, I dropped 300 loaded 30-30 cartridges onto the driveway, on the way to the truck. They were test loads for my infamous 30-30 Handi - the rifle from hell.
This rifle is now being used by the Vatican to train exorcists.