until Godfrey Reloading's Al Thornton advised me to get a small based sizer die. Also, the military uses a crimped case mouth, sealant on primer and case mouth and cannelured bullet on their ammo for a REASON.
I have found case stretching to be exceptionally bad on the .303. When full length resizing to reloading .303 brass 4-5 times, you better take a broken case extractor to the range when you shoot the gun. With .30-06 I have had 20 plus reloads out of the brass.