Congrats....
You are among an elite group now that you own a big-bore lever action.
I found that H335 is a great powder.
I used it with Speer 300 gr Unicor.
Try out this forum...dedicated to .444 Marlin.
http://www.marlinowners.com/forums/index.php?PHPSESSID=rq8p1f2i7pu2f86t159ql2j644&board=52.0