I like several definitions and some are conflicting.
The book "Dangerous Game Rifles - Second Edition-" by Terry Wieland, Mr. Wieland had a wider definition of "Big Bore" cartridges than some of you. This book is a good read, by the way!
Included as "Big Bore" are cartridges in the lever rifles such as 444, 405, 45-70, 450 Marlin, and bigger.
In the bolt rifles the "Big Bore" cartridges include the 375 H&H with a muzzle energy of 4500 ft-lbs all the way up to the - 700 Nitro which is listed in the appendix as a muzzle energy of 8,900 ft-lbs and mentions the 700 H&H without noting muzzle energy, the 577 Tyrannosaur, the 585 GMA, 505 Gibbs (6256 ft-lbs), 600 Nitro (7,600 ft-lbs)
In my opinion, he didn't seem to like the 577 Tyrannosaur much, mainly due to excessive recoil and problems with feeding in the rifle the cartridge was in..
He covers quite a bit in this book, including the big black powder , the lever, the bolt, the doubles, and the single rifles.
From my personal experience:
My brother owned a bolt action 50 BMG and I thought that was a little much for anything I'd shoot. The 460 Weatherby without a muzzle break was as much as I thought was comfortable to shoot, but that was 40+ years ago. I doubt I would think the 460 is comfortable anymore even with a muzzle break. Getting long in the tooth makes one have a different view on some things.
Good reference, its all perceptions. In the day a 450 blackpowder or even a 577 blackpowder express was not a bigbore. It was the medium for usually non serious stuff. Anything under an 8 or heavily loaded 10 bore didnt get classed as big whatsoever. Obviously what fellas talk about as big had to change when smaller nitro expresses hit the gamefields. That said there were references even to 450nitro class as large medium bores at first. Anyone drawing a 'hard fast bore size' rule for any of this doesnt understand history.
