I would think that it should work ok. If you are using the hot heavy magnum loads, it may be a bit short on eye relief with 3.5". I think that power range is about pointless on a 45-70, personally I would use a fixed power of 2.5x or 4x., maybe a 1.5x-6x or a 2x-7x is more than enough. If you want a scope in that power range, I'd look at a Nikon Omega 3-9x40, it's got a lot more eye relief at 5". If you are using the 325gr Leverevolution loads, I've read that the BDC 250 reticle on the Omega will match up perfectly out to 300 yards.
