I took my first moose up in Tannanna with a 32-20. And a Colt's 1917.
If you are talking 50 yards or less, a 50 will do the job with the right shot placement and a 250gr or larger slug. Moose have been taken with 44Mag quite well and the 50 with the right load is certainly enough.
That said, I would take the largest bore I had in stock. I would be very careful to place my shot high in the neck with the biggest bullet I could cram down the barrel.