I have always used a light charge of whatever I was shooting in the case at the time. The spring back will depend on the temper of the brass. If you have annealed it not much if you haven't more. This isn't rocket science just use a light load so you don't rip the neck off when turning 30-40 Krag brass onto 40-60, It may take you a couple of firings to get it to the shape you want and fire formed to your chamber.

40 Rod

Might want to read this thread on the same subject ...
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Hank, let's start from scratch:
*  What caliber cases are you using to reform from?
*  What caliber cases are you reforming to?
*  How many reformed cases have you or are you making?
*  List the nitro based and original gunpowder grades that you have now?
All of the questions have meaning.
For smokeless powder, you want to use one with a high Burn Rate.  If you are not familiar with the Relative Quickness of burn rates, here's a table ...
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And for black powder, the smaller the grain size is better

Quote:
Here's 2 high burn rate powders that I use and posted in the link for you to read.  Since you don't have either, your option is reload the fire formed cases with either FFg or FFFg - take them to the range and shot them.  Be sure to put a good crimp on the cases