If you are using the original military or 'field' chamber, you have to set the dies by your fired brass. My 303s are all field chamber. I smoke the neck on a fired round, then adjust the die to just clean off the neck. I try not to move the shoulder. My brass works in ONE gun. I have 4 SMLEs. I have to adjust my dies and mark my ammo accordingly. Dad has one SMLE. I set my dies by his fired round and reload them. I know they have to be on 4th or 5th reloading right now. He will probably bring me a box of brass on Thanksgiving, and I usually have them loaded and back to him at Christmas.
If you are full length sizing each time, you may have head seperations and/or splitting in the neck and shoulder area from over working them. If you only have the one gun, smoke a neck, adjust your die to clean the smoke off the neck, and try the brass in the chamber. The bolt should close with minimal pressure. After 2-3 firings, you may find your bolt getting a little harder to close on fired rounds. You may have to set the die down just a few thousandths to bump that shoulder until the brass easily chambers again.
You should get better than 3 loadings.
Steve