Many folks report loading .454 balls in their Uberti Walkers but some do load .457 balls and other are able to shoot with .451 balls.
I would suggest to try out the Uberti using the same .457 balls that your ASM takes to see if the same mold can be used to cast balls for both Walkers.
And if the .457 balls are too difficult to load, consider getting a smaller diameter ball mold based on some further experimentation and/or chamber measurements.
It's also important to cast balls from pure lead or they may come out oversize even if the optimum diameter mold is used. So having a pure lead supply can be just as important as obtaining the right size mold.
It would be a shame to invest in a .457 mold and then cast balls using an impure lead alloy only to learn that the resulting balls were too large due to using hard, impure lead.
IMO the Lee molds have a reputation for often being made very close to spec's while some of the steel molds can be slightly oversize to begin with despite being more expensive.
