Do not go to the 444 Marlin. In the rifle you have recoil will be brutal. Also you will destroy a fine rifle.
If you absolutely have to shot beyond 150yds go to a 260gr bullet. It will carry better than any 225 or 240gr bullet even though it starts at a slower speed. It will make up for the slower start & then some.
Yeah, that's what I meant about bringing a mob on myself, and it just feels a bit wrong, given there's not a large supply floating around. Regarding bullet weight, I did not know that. I will take that into account.
Check your rifling twist. I’m pretty sure the last of these was made in 85 or 86 and all the 44s has a 1 in 38 twist. I thought about the 444 as well but don’t think you would stabilize the heavy bullets to make it matter.
I believe mine is an 82, and though I've not researched the twist or the mechanics of how it all works, I had heard that it's a large thing to consider if you were to make alterations like that. Heading to the search bar now...not for modifying this rifle, just general education.