I have a BRNO 602 300wm,I want to rebarrel it to something with a lot more boom.I am considering a few cartridges,400H&Hmag,416 rigby,416 taylor.400H&H is looking like the one,with being able to make cases for it from 375H&H brass.Any ideas fellas how much work has to be done to the rifle for the 400H&H?