I'd add one more reason not to, if you ran the 45LC very much in a 45-70 chamber, aside from the brass problems mentioned by Steve and Daryl, over time I would think you would end up with throat problems in the 45-70 chamber, due to the sloppy fit of the 45LC brass and bullet dia difference and having a long lead(the difference in OAL being almost an inch)getting to the rifling. I could foresee gases getting by the bullet before it ever got to the rifling and just general misalignment from the diameter difference would wear on the 45-70 chamber pretty bad.

C