The .45-70 has really stood the test of time. It is available everywhere. Jack O'Connor used to talk about traveling to hunt and lost luggage. Where are you going to get a box of .450 Marlin at 2200 in Yellowknife?
I used to have a .444 Marlin and now have things like a .348 Winchester and a Sharps in .45-100. The .45-70 is a better answer because you can get Garrett and Buffalo cartridges loaded up and all the brass you want for cheap.
