Originally Posted by Brush4646
You don't have to go to 7mm08 brass just load the 243 bass with the bullets into the lands soas to hold the case against the bolt. Lube the case and shoot. Now back off your size die so you don't push the shoulder back again.
+1 for this, it's what I was gonna recommend... Just seat the bullets far enough out to engage into the rifling so that it will keep the case head firmly against the bolt face. Just don't fireform with max loads, back it of a little, but don't use overly reduced loads either, as the fireforming would not be complete then.