I've wet-molded heavy leather vise jaws for a few decades for all day use. I have bronze, square steel, heavy cast lead, light sheet lead and aluminum octagon jaws for other application. The leather is soaked, vise jaws closed together then they are tied in place with rope until they dry.
Note the cork-faced one in the background (behind gun barrel) Only used to clamp wood. Brownells sells perfectly sized heavy leather for 4" jaws.