In regards to the 31 caliber Pocket revolvers and any 31 caliber shooter, I've always read mostly they take a ball of .321-.323" in diameter. I've never had or even shot a 31 caliber cap gun so have no experience with them. Should be a lot on line ref their needed ball needs, can make a difference if it would be a Pietta or Uberti.
In regards to your 36 caliber Uberti, both of my 36ers like a .380" ball vs a .375. The .380 shaved a bit more lead and at least the time I compared the two, the .380 had a slight edge on accuracy. I've read where Pietta's prefer .375", while Uberti's like the .380's better. Buy some of both and see what works better for ya. I have no problem ramming the .380's into the cylinders of my Uberti 36 cal 51' Navy and Navy Arms Uberti made 61 Navy. I've tired conical's and big lube style bullets in my percussion revolvers (36 and 44's) and didn't care for them. Use .454" in my 44 caliber revolvers, except Ruger OA, it likes the .457's. I use a lubed felt wad under the ball with excellent results and despite Dicks advertising post, can shoot a lotta rounds downrange without fouling up things. Nothing personal Dick, just sayin'. Like your molds for my conversion revolvers.