A: Most books call for reforming .45 basic brass to make the 2.4" .40-70 WCE You should be able to just run .45-90 WCF (which is also a 2.4" case) into the .40-70 sizer and trim to 2.4" if needed. Starline makes .45-90 brass currently. Both RCBS and 4D offer dies. The RCBS 2-Cavity Bullet Mould .406" 41-300-FN will drop a bullet of about 320 grains cast from 1:20 mix, which should be perfect for your 1886. Buffalo Arms generally has all of this in stock, but there have been long stock outs on some product. Buffalo Arms also offers .45-90 brass redrawn from .45-70.
I'd stick with black powder, but dimensions and smokeless data are given in Cartridges of the World and the Handloaders Manual of Cartridge Conversions.
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