I have to agree here.
I'd rate the '73 winchester as a1.5- 2d6-1, out of a rifle it is similar to a .41 magnum in a pistol, iirc.
Especially the high velocity hunting load.
For the .45-70, etc, about the same damage, with a +2 stun mult, or a little more damage with a +1.
1.5-2 times the bullet weight at about the same velocity as a .44 magnum in a pistol, off the top of my head.