[RM2K3] RECOVER MP AS AN ABILITY?

Ok, so for context: in my game, there is a gunsman character who obviously doesn't need MP, so instead, I've been trying to get him to use an ammo system instead, where MP is the Ammo currently in the gun, and having a reload ability to recover minor amounts of Ammo, but I can't figure out how to recover MP? maybe I am looking something over, I'll look longer, but if anyone could help, it'd save a lot of my time.