Tool to stretch .50-70 cases

To montana-charlie,

Someone on the CBA forums told me that you might have a tool for lengthening .50-70 cases. I'm making my first foray into BP cartridges, loading for a Sharps New Model 1863. This rifle appears to have a chamber (has an abrupt step) that is about .150" longer than the Starline .50-70 Government cases that I purchased (1.748"). From what I've read, this extra space between the end of the case and the start of the throat might give me accuracy and leading problems. Any thoughts/comments for me? Thanks,

Russ