I am asking this in relation to 375 H&H and 375 Wby.

From memory a 375 H&H is about .3" from case mouth to rifling. Would be about .377" diameter at the start.

375 Wby is .375" from case mouth to rifling but Wbys use a parallel throat that is .0005" over bullet diameter, that is, it starts at .3755.

Which would be preferable for cast bullet shooting.

I would say the one with the throat that is closer to bore diameter.

Generally speaking, you want to size your boolits closer to throat, and let them swage down to bore.

The more undersize to the throat they are, the more leading and accuracy trouble you will get, all else being equal.

And that longer leade in the Wby will give you more options for nose length and design.

My $0.02.


Tim