Is there any advantage to using nickle 45-70 cases?

Only if you're storing them in a corrosive environment. That includes a chrome tanned leather gun belt. Otherwise they specialize in scratching dies. I wrecked a pre-carbide .45 ACP sizer die on old nickel cases.

Bye
Jack

. . . I wrecked a pre-carbide .45 ACP sizer die on old nickel cases.
Bye
Jack
Same here only it was a .357 Magnum die. Only reload with all brass cases now.

One man's junk is another's treasure! :D

I've always had pretty good luck with nickel cases. Trick is to make sure they are clean BEFORE running them into a sizing die.

nickel is slicker and is a bit thicker which helps with some of the heavier loads

but it sure does like to either split or last forever

My main reason for using nickel cases is tarnish resistance. If you were using black powder in your 45-70 cases it would work well there. I've had a in-line nickel plated muzzle loader for half dozen years and still looks factory new thanks in part to the nickel plating. I've had more trouble scratching dies by coral dust from cases picked up while shooting. These were acquired thirty-five years ago while in the military. I still get an occassional piece of coral grit from a case imbedded in the seizing die. The cases have been washed, tumbled etc. and still it occurs.

Have always believed the tapered wall case e.g. bottleneck, is treated more gently than the straight wall case by sizer dies. With tapered wall cases, there is a combination of sliding and compression forces during resizing whereas with straight wall, it's mostly compression and a lot of it. Combine the straight wall case with a poorly applied coat of nickel plating, and you have a situation begging for a scratched sizer die. Will be the first to agree that nickel cases can be resized with steel dies but given the choice of brass or nickel, I'll go with brass.

Along with my Rugers, I have a Model 29-2 S&W 44 mag. I use nickel cases for the S&W. I would not want to get Ruger loads mixed in with the S&W.