As you probably know, not all chambers are cut equally. FL dies resize the case, but not to SAAMI minimum or even close, in most cases. Depending on how you set up the sizing die, the cases may not have been fully sized. You may have to set the die closer to or on the shell holder to ensure adequate sizing of cases for use in the new rifle.
I would use the existing sized brass for load development. I would buy new brass for use in hunting loads and when sizing fired brass, ensure the die is set up properly to be sure that things don't go sideways in the field. Such fired and properly resized brass should fit much better in your camber.
