Kitch,
Crossfireoops' technique does work, but another option is to stretch the .45-70 cases. Buffalo Arms sells a very reasonably priced case stretcher made by Tim Smith-Lyon. The price is $39.95 + shipping. Here's an article that I wrote on the subject that you might find interesting.
http://www.texas-mac.com/Stretching_Short_Brass_To_Fit_Your_BPCR_Chamber.htmlWayne
Last edited by texasmac; 10/22/14.