I thought the same kind of thing recently about the .500 S&W Magnum.
I saw an H&R breakopen in that chambering, and thought "Gee that's kind of cool - what a thumper!" but since I don't see any need for ME to have a handgun in that round (I don't live in 'bear country' and wouldn't use a
handgun if I wanted to shoot something more than 25 yards away with a big heavy bullet),
I got to thinking...
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...what exactly can the .500 S&W do that a .45-70 can't do, except
a) fit in a shorter action (a non-issue since no short repeaters currently exist for the round, and there's always the .50 Beowulf).
b) no 'old guns' out there to accidentally put a 'hot' round in and blow up (hopefully a non-issue, since my only .45-70's are an 1895 Marlin and a Thompson Center Encore).
So, despite the 'fun-factor' of buying into a new cartridge, I just couldn't see it.
So I got to thinking again...
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...when you get right down to it, there are only 'bore sizes' and 'bullet weights' and 'velocities' - so for each bore size, you have a maximum practical case size for the type gun action you want to use, and THAT is going to meet all your needs. If you want extra
slow velocities most often, you might get there more efficiently (wasting less powder) by using a smaller case size.
If you look at the available calibers, from a truly practical/hunting standpoint, you don't need
every caliber; maybe just one each in the range of 5mm to .22, 6mm to .25, 7mm to .30, 9mm to .40, and .44 to .50 surely would cover it ALL. Even then, 3 of those 5 gives you a huge ballistic selection. Factor in 'action type' or handgun/rifle considerations, and you could really have 5 or 6 cartridges cover everything. (i.e. .22LR, .22-250, .32-20, .308, .44 Mag, .45-70)
And . . . they could be old or new, short or fat, rebated or rimmed, and it really doesn't matter downrange! If you don't believe ME, just ask the deer, the bears, and the prarie dogs.