Thanks for the comments.
I sent Lee Precision an email asking about the different diameters for their various 45-70 moulds and got this reply:
"Over time the inventory of molds that are manufactured and sold by Lee has been refined by the natural selection of customer demand. The .457" diameter bullet designs are the ones most commonly requested and used diameter so that is what Lee offers as standard inventory. This diameter tends to give the best all around performance in this caliber.
The two exceptions are the hollow base 459-405-HB which is typically used in vintage firearm that have worn or oversize bores. And the 459-500-3R that is a favorite for long range black powder competition."
All of what has been written in this thread is good food for thought. Much appreciated.
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