.490 - .450 = .040 45/70
.451 - .421 = .030 .44 Spec / Mag
Really only dealing with .010 more ball with the .490 in the 45/70.
Really do like the rolling between plates suggestion and may well use that for .30 Cal bore. Using a .32 ball did not leave much of an area to mic.
Might start using egg sinkers in those.