The difference in diameter of a .454 and a .457 ball is so small, that after you shave off the extra width, it should pose no problems.
Remember that even revolvers only can efficently shoot a maximum amount of powder.
The formula is still 11.5 grains per cubic inch of bore, only you can add the length of the cylinder to the length of the barrel. If we assume that your revolver has an 8" barrel, and a 2" cylinder, for a total of 10" of "bore", a .45 caliber revolver will only efficiently burn 18.3 grains of powder in it. That is not a milktoast load, BTW. A more accurate powder charge, using 3Fg powder, would be down in the 12 grain range. /A filler on top of the powder charge to the base of the RB will give you the best accuracy.
I am sure, if you are like I was when I owned a brass framed revolver, that you are putting more powder in that chamber than 20 grains. You not only send unburned powder out the muzzle, but the burning powder and gases created behind the round ball or conical will be rushing past the edges of your muzzle, and creating turbulence in the air in front of the muzzle. If the muzzle is not square to the bore, and if you don't have an 11 degree taper to the crown to allow the gases to expand normally when they exit, you are going to get flyers, no matter how good a bore you have, or how accurate the sights are. You will also beat that brass frame with the cylinder recoiling rearward, so that the brass stretches, or develops a groove in the recoil shield that matches the rear shoulder of the cylinder.
When that round groove gets deep enough, the edge of the frame at the loading port will ignite the percussion cap on the chamber aligned with it, when the gun is fired, and you will get a double fire-- one down the barrel, and the other along side the right side of the frame. Often it will nick the barrel key and ricochet off into the dirt to your front left. Either way, when you have created that condition, the gun is dangerous to fire.
You could have a machinist cut you a washer from steel to fill the round groove, or you can scrap the gun for parts, and get a new one. Keeping the powder charge down to what the gun can burn efficiently, or less, will extend the life of the gun for years, and keep the frame from stretching. :thumbsup: