AC,
I still stand behind my statement that your assertion that the .450 Marlin is more powerful than ANY .45-70 load is erroneous.
I saw no indication that "we" were talking only about leverguns.
I've fired the .450 Marlin in a Steyr boltgun & found recoil was noticeable, but hardly unpleasant, and I don't consider it to be a huge thumper.
On the other hand, I have loaded (and safely, after discussion with a couple ammomakers) my Ruger up stoutly enough with various .45-70 handloads that it took several hours to get over the headache and a good part of a week to get over the shoulder pain after a typical range session with it.
Those loads were not even max in the books, and a couple of the Sierra loads were already compressed enough that I didn't even try to get near max in the figures I got from a couple manuals and confirmed directly with Sierra.
No signs of excessive pressures in the brass, and the Ruger rifle's action can handle it easily.
I was producing around 2150 FPS with 300-grainers, 1890 FPS with a 400-grainer, and so on, in the loads that worked best. Those were also not necessarily the fastest loads done with each bullet, just the most accurate.
And, no 24-inch test barrel.
The 28000 SAAMI max figure you quote from Hawks regarding the .45-70 ceiling is strictly for the older style Trapdoor and similar guns, as it clearly states. In the Marlin, there is no reason why the .45-70 cannot be loaded to exactly the same velocities, and safely, as the .450 Marlin.
In a Ruger #1, both can safely exceed Marlin level loads.
The entire reason for the .450's existance is to produce hotter .45-70 level loads in brass that can't work its way into a weaker action than the Marlin chambered for it, it was not created to be "more powerful" than the .45-70.
If the two calibers were ONLY available in the Marlin leverguns, you'd see identical pressure ceilings from SAAMI. Since they're not, SAAMI doesn't mind releasing a realistic figure for the .450, but won't go any higher than Trapdoor level in the .45-70.
Not trying to put the .450 down, just taking issue with your statement that it's more powerful than any .45-70 load.
Denis