I must still be at relatively low pressure as only 1 or 2 of those rounds seemed fully formed. I'm going to step it up to the next lowest max charge and that should do it, I would think.
I had problems with fire forming a .280 GNR one time, which is a .405 Win necked down to 7mm with 40 degree shoulder. I called Garry Reeder who markets the cartridge, he told me to properly fireform the brass in needed to jam the bullet into the lands to help increase pressure to move the shoulders forward. My problem was I was loosing about 1/3 of my brass to split necks and the shoulders wouldn't properly form untill the second firing.
I was scared as well to use his fire forming loads because they sounded hot to me as they were near max loads for the 140 grain bullets. His loads called for the use of a magnum primer and I substitued a regular primer again because this was my first time fire forming AI brass. However jamming the bullets and following the load data cured most of my fire forming problems, but I still had the occasional split neck. )nly annealing the brass after necking down solved that problem 100%, and I annealed as well after the first fire forming load as well since Gary suggested that if I was still having necks split after I followed his instructions.
I was work hardening the brass as I was having to step down in stages the necks. I used a .35 Whelen die with expander removed first pass, .30-06 die for the second pass, and the .280 GNR die for the last pass. Doing this created a false shoulder, but of course since you can buy .243 brass you don't have to worry about that. Playing with wildcats and AI's can have their challenges, but it is a lot of fun.