I don't know either, what you gentlemen class as BIG BORE but I'm pretty sure my Steyr 50 makes it on all counts. Nothing cast in stone yet but hoping to take it for caribou in Oct up to the barrens. All sighted in out to 1 Km and would love to dump a couple bulls way out there.
Just to clarify, big bore in terms of dangerous game starts at 45 cal and 5000 ft/lbs of energy, according to John Taylor. The .375, .416 as well as .404 and the like are all classed as medium bores and anything under 375 is classed as small bore. There was a time when only .577 and up classed as big bore, given the limitations of black powder.
45-70 and the like meet the bore criteria but fall far short of the energy requirements to qualify for a true big bore. I realize that when talking NA game it is different and even .338 is considered to be a large bore given the animals being hunted. So I guess if you boys want to call your 45-70s and 450 Marlins and the like, big bores in the NA context, so be it.
Personally I like Taylor's classification and use it when describing the calibers and cartridges I shoot, I think a lot of us old boys and even some younger guys with African dangerous game experience would agree with me on this.
I don't consider my 45-70s, 45-90s, 45-110, 405, 40-72, 40-82, or even 50-110 or any of the old BP NA cartridges to qualify as big bores, any more than most of us would consider any handgun cartridge chambered in a rifle to qualify as a big bore, regardless of diameter.
And as always, even though this has been the standard for more than 100 years, when smokeless powder caused the re-evaluation of bore classification, it is still JMHO.