First thing to do is run the 444 Marlin brass into a 44 mag sizer just enough to square up the case mouth. If the case mouth isn't square a wrinkle will form in the neck. Now run the 444 Marlin case into a 308 Winchester sizer die so you have to snap the action shut on a sized case. You will have to go slow and adjust the die a little at a time to achieve this. Your going to love this round. I shot a buck last year at 240 yds with my 309JDJ!