Um ok I THINK I can help explain...
The original 458 was "hot loaded" a compressed powder charge that was backed off by Winchester after some blown up rifles (i think i read that in "Safari Rifles by Boddington) anyway the result was a cartridge that was NOT as good as the .416, or .470 (expensive english calibers) on VERY large dangerous thick skinned game (read that as Rhino, Elephant, Hippo etc.) Those cartridges deliver over 5000 foot pounds of energy at the muzzle.
Buffalo, while tough IS NOT a pachyderm. I've read both camps of using solids AND soft points to take Buff. Boddington advises loading your magazine with 2 soft points on top of a solid. If you NEED the solid its to get the most penetration.
Ok while the 45-70 is a good old american bison caliber its NOT a DG rated caliber. Period. Don't care if you roll your own, have killed what ever with it or use Randy Garrett hammerhead bullets. There are RULES for DG that were set up early in the 1900's to PROTECT hunters by "using enough gun".
Ok so "Karamojo Bell" killed elephants with a 7x57. You aren't him.
Bottom line is there is NO factory load (except MAYBE Garretts) for the 45-70 that develops over 4000 foot pounds of energy at the muzzle. In fact in winchester loadings, the 45-70 has HALF the power of the 458. HALF!
Now that means a 300 grain winchester 45-70 has 2355 foot pounds at the muzzle, compared to a 500 gr fmj from the .458, which rates 4620 Foot Pounds!!!! Its Not going that much faster but it weighs 1/3 again as much AND is flying at 200fps faster.
On paper Remington's 405 gr. load is even WORSE. The 405 travels at 1330 fps and deivers 1590 foot pounds at the muzzle that's a THIRD the power of a 458. A Third!
(source Shooter's bible ballistics tables)
Wet newspapers? What does that have to do with heavy bone, muscle and gristle?
Botton line is the 45-70 is an old low pressure cartridge. Its more than CAPABLE of taking large game. But its NOT a DG cartridge, not by African standards. The "new 458" by federal uses a 400 gr solid bullet at 2390 fps, delivering 5030 foot pounds at the muzzle. There is NO 45-70 that can do that.
Now I realize bullet design and hard cast etc can do a lot, but CAST bullets CANNOT be fired at high velocity, you'll lead the barrel. What you want is a HEAVY well made bullet at medium to high velocity. To get over the magic 4000 foot pounds. Garret just keeps the velocity down and makes the bullet REALLY heavy which increases its muzzle energy, but at low velocity it sheds power rather quickly, compared to a high velocity cartridge, say a .375. IE you get a rainbow like trajectory, and it gets worse the heavier and slower you go.
You COULD take a 45-70 to Africa but there are very few countrys that would ALLOW you to hunt DG with it. You are far better off with a .375 (the DG MINIMUM averages 4265 foot pounds of muzzle energy).
Hope the info is helpful.