I don't know what's the hoopla with moose shooting with a zillion fps wondergun. Back down here, for one moose shot with a 300 mag, 10 fall to 270, 30-06 or 308. IMHO, shoulder shots are a bad idea on something that would feed me for a year, a heart-lung area shot generally brings down the beast within a mile. On an animal this big and profusely bleeding from a lung shot, tracking if far from being a problem... just look for the tightest bunch of s**t, as Bad Med said earlier, tight enough that you can't figure out how a moose could have gotten in there head first, it'll be lying in there somewhere!
As of caliber selection, if you want a sledgehammer, I humbly suggest 375.
Cheers!