Alright, I'm curious and intrigued....
Firearm limitations or integrity set aside let's talk true cartridge potential. I have some serious curiousities.
What can we do with these "old" cartridges? You know, the 450 Marlin can push a 250 gr. Barnes at 2400FPS ish, cool. Most handloaders of the 45-70 know this is obtainable in the right action. It can also do great things with 405 grainers. From what I've read and understood the longer cartridges from the 45-70 can do better with similar or lower pressures. Let's leave black powder out of this and keep up with the modern theme of the thread, different hobbies/interests/specuations, no offence meant to black powder enthusiasts, bottom line, that is fun stuff!!!
Let's try this, what has been done with light weight loads in the 45-70,90,110,120, and in the same breath the heavy stuff, the 405, 450, 500 and so on also intrigue me. WHAT'S THE POTENTIAL??? Can we touch 458 Win? With the disclaimer of firearm durability left aloof...
for some comparison, a neat article about the 444 marlin was in last months G&A. Cool thing about that is that the 444 Marlin is "similar" to the 45-70 dimensionally but has the availability of 180, 200,240 (of course) and so on for bullet availability. Imagine the fun we'd have with a 200 grain copper bullet in the 458 caliber.
Let them roll and let's have some fun!