The .45-70 cartridge was originally designed for the Army but was too big for anti-personnel uses. Too much power and was unnecessary. Luggy around a 7 pound rifle all day that could kill an elephant was unnecessary. They were also used to kill buffalo as well. Then they started seeing use a good dangerous game rifle, due to its short barrel length, fast cycling due to lever and high capacity tubular magazine a lot of hunters/hikers/homesteaders/ranchers started using them to defend against the great bears or any other large marauder like a big bull moose in full rut.
One important thing you should keep in mind is that factory .45-70 loads are down-loaded by the manufacturers for example the 405 grain remington soft points or 300 grain hollow points that are sold all most anywhere including wal-mart. The manufacturers put LESS POWDER in them because they don't want people putting it in some 120 year old clunker and trying to fire it and the gun blow up in their face. Thats why you hear alot of people say that .45-70's are underpowerd for dangerous game or inaccurate... thats cause they are firing the $20/box junk ammo thats down-loaded to prevent LAWSUITS. Factory .45-70 loads are great for deer or black bear sized game, and plinking, however there are a few manufactueres such as GARRET cartridges, Buffalo Bore, Double Tap, Cor-Bon, and Grizzly Ammunition who make .45-70 ammo that can push out a 430 grain bullet at 2000 fps... thats way more than any 1oz slug in a rifle shotgun. not event oo expense about $60/box for most of these... expensive but still half the price of any safari caliber box of ammo
This guy named VINCE LUPO took Africa's Big Five with a .45-70 marlin guide gun, he used Garrett cartridges to accomplish this feat. He used the 420 grainers and 540 grainers from hard cast lead. Both made from hard cast lead and powerful enough to penetrate and down all big 5 ssafely and effectively