Jim,
Own and shoot a 444, a 1st model Marlin rifle with micro grove rifling that I bought in 69 or 70 as I recall. First thing, check the seating plug in your die, it may be for the flat nose, solid 240 that the factory rounds are loaded with. When you seat a HP bullet with that plug, it tends to crush the edges of the cavity, as the case is crimped. You might want to get a RN plug from the die mfg.
As with all rimmed and crimped cases, it is very important that you trim all cases to the same length in order to get consistent crimping of the bullet.
A few hints, I have found, in my particular gun, 4064 to be the most accurate powder with jacketed bullets and Unique to be about the best with cast. If you have a source, the 444 shoots the 215 and 240 lyman SWC GC bullets real well. The old Lyman books list accuracuy loads with the Marlin and the loads are pretty good loads, right off the shelf. Suggest you use large rifle primers and not magnums. Oh, check your bullets, some companies list their bullets as .429 when in fact the bullets are .428 If your bore diameter is .429, the .428 bullets might not give you the best results.
You might want to pick up a decent low power scope with a with a very wide field of view and a tip off mount. I have a 2x (36' @ 50 yards) with a Weaver mount and find the mount returns to zero every time. I like the low power scope in the woods better than the naked eye. The scope also helps a great deal for load development.
Good shooting and best of luck with the new toy.
Ed