Blacklab, I'm curious, after the first load work with the CCI400's did you reload that same brass and then switch to the BR4's??
Also, with the first loads and the CCI 400's, was this virgin brass or maybe the first time this brass had been shot in this particular gun?
I'm asking because if the brass was reloaded using same load but with the BR4's and the brass was now fireformed to that particular gun, groups tightening up that much from load to load would maybe make a little more sense. Usually, primers alone, don't improve groups that much but certainly anything is possible.
Regardless, it definitely looks like you have a keeper.
