My Marlin shoots better than I can milk it for with .459 diameter. I bought a box of Laser Cast 350 grain bevel based flat points. I shot them with a load of Trail Boss. They shot to point of aim at 25 yards with no problems at all. No lead in the barrel at all.
Though I am waiting on a Lee .459 405 grain hollow base mold for casting my own. I will report on how those do when I get the mold, and load some up. If the mold gets here this week I will cast some, and shoot them this weekend weather permitting.
No matter how many times you do it and nothing happens it only takes something going wrong one time to kill you.