It is usually easier, and much less expensive, to find .303 than .30-40 brass. I find the Prvi brass to fit the chamber of 3 different .303s (all, admittedly either very late or post war rifles FTR'd and put away waiting for the Russkies coming through the Fulda Gap) better than most brass. It works as well for me as my Greek surplus brass, I've never had a bulged case with that brass (wish I had laid in several cases of the .303 and bought the same of the .30-06 when it was on the market - hindsight is 20/20).