When you resize brass for a break open rifle it is a totally different game. It is not like sizing for a bolt action. Go to the web site that Mike Bellm has for single shot rifles. He goes into detail exactly how to size your single shot brass.

In your single shot you have your cartridge headspace-then you also have to add the length of the gap between the end of the barrel and the breechface. How large that gap is will determine if you can NS or not. If the gap is too big then the shoulder will need bumped-If you do not bump the shouder the rifle wil not close properly. Tom.