krochus: The Model 444 is basically an oversized 336. It was re- designed for the cartridge. Mine was a honey, stonger than snot. It is not a psuedo 1895.
Microgroove rifling - no benefit to the use of cast, gas-checked bullets unless it has been firelapped. If not, you can stick with jacketed slugs from 240 to 300 gn, or possibly heavier. For many of us, the 444 really shines with hardcast, gas-checked slugs that can easily exceed jacketed slug velocity and the microgroove barrel will turn out excellent accuracy (see Beartooth Bullet website). I question whether there are any benefits to the use of Ballard rifling over a properly lapped microgroove barrel for cast bullet work but I could be dead wrong on that one.
I believe the firing pin on the older Marlins is captured by a recoil spring. I do not believe the hammer resting on the firing pin causes the firing pin to rest on the primer. Don't they have a half cock?? Mikey.