:DHey Kombi.Ellwood Epps developed all sorts of cartridges off of the 303 British.He went from 22 cal up to 375.One of his favorites was the 303 epps improved,40 degree shoulder short neck minimum taper.
you can get info from.
www,ellwoodepps.com
They have
books on the 303 imp.I'm shure they would sell you one and just mail it to you.
Lots of info on the cartridge.
email them and say that Frank. S. told you to.
Happy shooting.
ps they have chambered barrels for 303 epps imp. and mailed them to Austraila.