The most important dimension is the throat. Lead bullets should as close to throat dia. as possible. This keeps the bullet straight when it get slammed into the bore, if the bullet tilts, pushing bullet center line off ballance, due to too small a dia to fill the throat, it will never be accurate. Marlin suggestd some good sizes for lead bullets.
I seat my .432" gas checked bullets in my .444marlin so that the last 1/4" of lever travel is pushing the bullet into the lands enough to show slight rifling marks, I crimp with a lee factory crimp die when this length is reached, not in the "universal" crimp groove. This made all the difference in the world and is worth a try, with a slightly lighter powder charge of course. The key is to keep them straight, ballanced, from ignition to muzzle exit.
My marlin is very accurate.