Moose die easy, but problems start because they can take some time to get around to it. Any of those guns will do the job, but....
In places I hunt, you really want to drop them as quick as possible to keep them from wandering out into the middle of a pond or dense tangle of willows before they get around to dropping. Assuming you're using a stoutish load in the 58, I'd pick that over either the 50 or 45 simply because I believe it will drop one quicker. Heck, on my next moose hunt I plan to use a 62- not because I think it will be even better than my 58, but because it's kinda new and burning a hole in my pocket. :grin:
Best wishes on your hunt.
Gotta throw a Bush Alaska trick in your plans. Fold up about 3' of waxed paper and put it in your kit. When you dress the moose carefully peel off the thin lattice of fat from the paunch (we call it "lace") and hang and spread it on a bush to cool and stiffen while you do the other chores. Once it's cool, fold it in that waxed paper and take it home.
Back home, wrap it around a big roast before baking. It's so much better and sweeter than bacon and keeps the roast so moist, you'll be wishing your next moose came outfitted with about 50 pounds of lace!
Heck, one more: Long as we're talking Alaska, if you like beef tongue you'll love moose tongue. If you've never removed a tongue before, start by making a long "V" cut along the insides of the jaw bone under the chin. Extend it well back down either side of the tongue into the neck. Pull the tongue down and out from the jaw, and sever well into the base of the tongue. We're talking a great big hunk of meat here fully as big as a beef tongue. Prime eats.
