Dr J,
I have a friend with an overbored 44 magnum Marlin, and he finally got it to shoot well with 240gr XTP's over a maximum load of 296. As noted above, Hornady XTP's are .430 in diameter, and should shoot well in your gun. My handi rifle measures .431, and 240 grain Winchester factory loads (white box) give me adequate hunting accuracy. Give them a try. I pulled bullet and measured it, and the Winchester also seems to be .430 in diameter. In my gun, full-power loads shoot best, but I'm having trouble finding a light target load that shoots well. I did just buy some .432 diameter gas-check lead bullets from Montana Bullet Works that are showing some promise.
LaOtto, could you be mixing up remington and winchester? The 44mag Winchester bullets I have measured seem to be .430, whereas the Remingtons that I have measured seem to be .429. Or maybe I'm measuring wrong.
Duane