I have a frame into H&R right now for fitting of a .444 barrel, it was finished earlier this week, but they're doing some testing on it Monday with the 265gr Hornady Light magnums and the Leverevolution ammo. It's one of the first barrels off the production line. When I get the results of the testing, I'll share the results.
The New .444 NEF will have a 1:20" twist rate instead of the obsolete 1:38" of the original Ultra and older Marlins, should make it shoot as good as the current production Marlin .444s. These barrels will be broach rifled by Marlin, they slug at .4248" at the lands, and .4308", in the groove, since these are new broaches, they will cut at the outside tolerance of SAAMI specs, as they wear and are sharpened, they'll cut tighter bores, but that won't be for about 1000 barrels.
Here's some cast data from Marshall Stanton at Beartooth, scroll to the bottom of the page at the link below, lots of cast bullet data for the .444 there. There's also some a bunch more cast and some jacketed data on their Loadswap page.
Tim
http://www.beartoothbullets.com/tech_notes/index.htm
http://www.loadswap.com/
