Marc,
I believe the 10x46R is the 10mm version of the several old cartridges based on the 46mm long version of the "MB" case.This cartridge would be more or less equal to the old American 40-60 Win. I recently bought a BF in 10x42(the little brother to the 10x45),but haven't started to load for it yet.It would be interesting to work with a 10x46 at the same time.BTW the proof on mine is 1893-1912, so 1880 would be a little early for the drilling.The crown"V" on the dollshead shows it was in stock when the proof law came in to effect in early 1893, so it must be early 1900s.
Mike

Last edited by Der Ami; 02/06/14 11:28 AM.