I only load for for 1 Enfield. I learned my lesson full length sizing and threw away 50 separated cases. They shot fine but I needed my separated case sxtractor. Now I use a Lee collet die with Prvi cases only. With the other rimless calibers i shoot all brass remains with a specific rifle never changes. Hornady 174 shoots best for me, I used it at Ben Avery for the Vintage Sniper Match. I use the flat base round nose for our 100 yard club matches. Measuring headspace is not something I consider with the 303. I did use the o ring technique to get straight cases but gave up since I am easily distracted. I have noticed tight chambers make a big difference. My friend has a Mark 4 #2 that drives tacks. With a vernier sight he can shoot better than my Mark 4 T with scope.