Hi there, have you shot it yet, if so with what ammo and how does it shoot? Some guns with over size cyl throats shoot just fine with the standard .452 lead dia bullet and some dont, you never know till ya try it out. With factory ammo the Remington 255 LRN has a very soft .455 dia bullet with a bit of a hollow base that should slug up and shoot well for you. If you handload, a bullet smith out there may be able to supply you with .457 dia bullets. You can buy the Remington bullets in bulk through Midway. As for jacketed bullets your selection of bullet diameters are rather limeted and dont come anywhere near your size im afraid, once again try some and see how they work out. I hope this helps you out a bit!