Use small base dies if possible on Semi-Autos
I am not sure if they are offered on magnum rounds, but I was always told to use small base dies when reloading for semi-autos. I have a set of rcbs small base dies in 30-06 that I only use when loading for semi-autos. They reduce the entire case slightly more and aid in chambering. Hopefully someone that loads magnums for a BAR will chime in if they need small base dies in the magnums.