Sharps-Nut: I believe the Marlin bores are oversized. The rifling, whether Ballard or Micro-groove will shoot jacketed bullets fairly accurately, but 2" at 50 yds isn't accurate in my book and shotgun patterns with cast bullets is not good at all.
You should slug the bore on any Marlin rifle to determine its bore diameter, then lap the barrel to remove any roughness or minor obstructions. Go to Veral Smith's Forum (Ask Veral Smith) for his thoughts on fire/bore lapping and then go to the Beartooth Bullets website to see what Marshall Stanton has to say about it, get the necessary materials and git'r done. This process works for any bore, 45 or 44, 454 or 444 - I'm such a dang poet.......but it works. HTH.