The 3 1/4 was once a black powder round. The 3 inch has always been a nitro round.

Actually, the 3 in will do everything the 3 1/4 will with a bit less pressure. Reloading the 3 is a lot easier than long necked 3 1/4. But hey, that's just my experience!

My personal opine here, the 450/400 3 inch is a prettier round than the 450/400 3 1/4. Life is too short to hunt with an ugly round!

Once again, just my opine!