The only time I had problems with my 12 F/TRs not lighting off rounds were ones that I hadn't seated the primers fully. Between the tight pockets of Lapua .308 brass and a hand priming tool... I thought they were seated enough, but they weren't. Switching to a different tool for a time and making sure the primers were bottomed out in the pocket (without crushing them) fixed the problem. FWIW, I took the rounds that didn't go off home and on a lark, tried firing them again. Bang bang bang. Apparently the first whack with the firing pin seated the primer just fine... not that I'd recommend that, certainly not in a match!

Otherwise... I agree with Jon - you probably want to check headspace of fired rounds with a proper comparator tool (Hornady, Sinclair Int'l, Forster, etc.). Its entirely possible you're over-sizing the cases and the firing pin strike is shoving them forward in the chamber if they are way undersized. The 10BA might have just enough more firing pin protrusion that enables it to set those rounds off when the 12 BR is not. If you are getting 9-14 thou difference between fired and the bolt not closing at all... either something is off, or you are pushing on the bolt handle too much. On a couple chamberings that I don't have headspace gages for, I usually set the barrel headspace so *one* thickness of tape (masking tape being 3-4 thou in thickness on average) is all the difference there is between the bolt handle closing normally, and starting to feel resistance. I can muscle thru more than that... but thats not the point of the exercise here.