If you handload, the .45-70, in the Marlin leverguns, can be pushed to supercede the .450M, not by a lot, maybe a 100-200fps advantage, but chronographic testing proves the .45-70 IS a stouter load in the 1895's, not by much, but it IS faster with the same bullet.

I prefer the .45-70, I reload and can create loads that are quite impressive. If you don't handload, you're stuck with one or two manufacturers and one or two loadings each, IF your local store carries them, and you're going to pay a good deal more than .45-70 factory loads, which are available from almost every manufacturer and in several bullet types, the only problem being that they're loaded about 300-500fps behind the .450M or .45-70 max loads. If you reload, the bullets and powder are the same, case capacity is almost the same, but dies and brass for the .450 are more expensive.

Another problem I've noticed with the .450M, not all chambers are exactly the same, so certain guns will headspace on the belt, while others will head space on the case mouth, which if I recall correctly, is where it should be, this is also different with different ammo manufacturers, careful handloading alleviates this, but if you don't take it into account your gun won't shoot well, and it can be as small a matter as magnitude of crimp, too heavy and your headspace changes from the mouth to the belt, and your accuracy is changed.

That's not an issue with the .45-70, like I said, even if you don't reload it, that can be a problem with the .450, the .45-70 doesn't have that problem.

Here's what I tell everyone else, if you reload, or ever plan on it, get the .45-70, it's cheaper to reload and you can push it beyond the cusp of the .450M, if you don't reload, the 300-500fps advantage of the .450M might be worth it to you, the .45-70 is plenty powerful, but it rainbows a lot, the .450 alleviates this, BUT, it costs more to shoot, more to reload and doesn't get to the same top end for the reloader, factory headspacing can be problematic, and you're stuck with only a few manufacturers and bullet types.

For me, the .45-70 is better in either case, but people want a flatter shooting round, and if you don't reload, the .450M is faster and flatter...not like you really have to be picky with your bullet selection in rounds this stout