I think a reasonable guess will be that the .480 should pick up velocity similar to what a .44 mag does when it goes from a handgun to a rifle. A lot of loading manuals have data for both rifles and handguns so it's pretty easy to estimate the difference. ~300fps? That would be my guess, maybe a little more, depending on bullet weight.
Energy, trajectory, etc., should be pretty easy to calculate from there.
I agree totally with Mike. I wouldn't expect too much more that a 44 mag. with the same barrel length. The Winchester won't be a "poor mans Linebaugh" either. You see, the Winchester BigBore is dead (***), and this caliber will be in the standard 1894, which can't take a steady diet of high-pressure loads. The .480 is still in the same class as the .44 magnum, and the hot-loaded 45 Colts. The extra bullet diameter could be handy though...
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