I get an "ouchie" just thinking of a .303 Epps Improved chamber in a No. 5 MK. 1 - that scalloped knox form doesn't improve strength. Fortunately, standard ammunition should actually show less pressure in the over-sized chamber. IMHO, re-sizing a fire formed cartridge case, even with a standard .303 Brit. neck sizing die won't help case life, due to the reduced body taper of the fired cartridge case being constantly re-worked.