Mine sagged horribly under just my overnight load, I wouldn't even dream of putting anything significant in the load shelf. Is it doable? Probably, I don't see why a quarter wouldn't fit. And I doubt the frame would buckle/break under load. But based on using one for a little over a year across multiple hunts from early August to late November, the load carrying capacity (pack's ability to actually distribute weight to your hips from your shoulders and back) is comparable to my old badlands superday.
Moose are big critters, we've hauled out a few in my fam. I wouldn't trust a Metcalf to help me get it out.
EDIT: Specifically, mine had the newer Guide Lite MT Frame, which is shared by many of the expedition type packs from Mystery Ranch. It's not the Metcalf bag that I had an issue with necessarily (though in practice, I think the pack design and layout sucked). So to be more specific, I would avoid the Guide Lite MT Frame.