I use .430 when reloading my 444 with jacketed bullets.On loadswap, there are a couple of good loads with 265gr. and 300gr. Hdy. and Speer bullets. Both shoot very well out of my guns. You'll see a bunch of Hardcast loads that shoot as good if not better than jacketed bullets and are easier on the barrel. Always reduce data 10% and work up slowly watching for signs of too much pressure. Take care.
Marlins tend to have diameters on the wide side. To be sure, slug your bore but... a .432 cast bullet seems to be the right diameter most of the time (this is not an issue with most jacketed bullets). A Micro-Groove barrel shooting hard cast lead alloy bullets of the correct diameter can be among your most accurate rifles of similar action types.
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