I use to cast bullets for sale (and my own use) in many different diameters. (includeing .458") What i've found about hardness is, if it's too soft it will lead, and if it's too hard it will break up instead of expand on game. "Depending" on how fast your pushing it, the diameter of the bullet, type of lube, how rough your bore is, type of rifleing ect.. ect... will "all" make a difference is where that line is.

There are NO answers set in stone to what bullet will work in your rifle to do what you want, but i'll bet you in a 45/70 no cast bullet will "out perform" those 300 grain partitions!!!

I can tell you, if you use cast bullets for smaller game and practise, that fine line i talked about above gets a lot wider as you don't have to be so picky! That's what i always did and it worked out well for me.

Drilling Man