You gotta love 500 Grains' quote,

"The problem is that a 45-70 has anemic velocity when using a 500 grain bullet (1550 fps), which in turn leads to abysmal penetration. The 458 Win Mag with its original loads of 500 grain bullets going 1700 to 1900 fps would not reach an elephant's brain on a frontal shot. There is no reason to expect superior performance by dropping the velocity another 300 fps."

Never put more clearly, in fewer words and with more common sense!

JPK