Between my sons and I, we've had three .44 magnum Marlins...all had Micro-groove rifling and all had bores that mic'd 0.432"+. We've had good success with both Jacketed and Cast bullets with them, and without tinkering with the barrel bands, free floating the fore ends or glass bedding anything. Accuracy with factory ammunition (Winchester White Box 240's), runs less than 3" at 100 yds with peep or 2.5x scope.
For cast bullets we use gas checked designs: Lyman's 429244gc & 429215gc. We size them to 0.432" for the Marlins and 0.430 for our handguns: (3 Smiths & 4 Rugers). Accuracy is 2" or less at 50 yds, with a peep sight with all of the carbines. Alloy: wheel weights + a bit of tin to facilitate mold fill out (bhn 12). GC's: Hornady, annealed (heat them with a torch so they'll grip better when the bullet is sized.) We don't push velocity in loading, looking instead for accuracy which generally comes from 110 to 1500 fps muzzle in the Marlins. That's plenty for deer with a rifle...they're great plinking/practice bullets, but have plenty of penetration for hunting as well.
If you're having jacketed bullet accuracy issues with your Remlin .44 (despite the bore size) the gun is not set up right or there are other issues. All of our Marlins, (bore sized 0.432"+), will put 200 gr or 240 gr Hornady XTP's into 3 inches or less at 100 yds from bench. With these bullets, muzzle velocities run 1600 to 1750 fps...they're definitely not top end loads, but are proven deer killers out to 100 yds or so. BtW, Win White Box 240's clock 1700 in our guns (20" bbl's).
Lastly, with regards to cast bullets, use the largest dia. bullet you can get that will chamber in the gun. In our use, 0.432" does fine if you don't overly push to maximize the load. If you can't get 0.432" or larger gas checked cast bullets commercially, a smaller size may do if you keep the velocity down to 1200 or less. (Try 7.5 to 8.5 of Win 231 or Unique)
Also, with real Keith type LSWC's, the front driving band may hinder feeding. The best we've found to date is Lyman's 428215 GC...a 225 gr LSWC design. It feeds 99% of the time in two 1894's and my 336 (yep it's a 336 chambered in .44 Mag). This is our go to bullet for all of our .44's, rifle or handgun...great accuracy, economical in times of wheel weight scarcity, and casts like a dream. Given only one .44 bullet for all uses, this'd be the one. Alloyed 50-50 with pure lead/wheel weights and hollow pointed with a suitable mold or with a Forester Hollow Pointer, it will give spectacular expansion with a muzzle vel. of 1100 fps or more. Easy in handgun or rifle.
In any event, with any commercial bullet, whether for handgun or rifle, I strongly suggest re-lubing (Swirl method) with Lee Liquid Alox thinned out with paint thinner (1:3, LLA to PT). It'll help/eliminate leading issues. Pushing velocity with an undersized cast bullet is guaranteed to lead your bore. If you do get into leading issues, remove it with ALL COPPER CHORE BOY scrub wrapped around a well used bore brush.
Our experience is that with Marlin Micro-Groove rifling, you need to use a Gas Check, use as large a bullet as will chamber, and don't push for max velocity.
HTH's Rod