I had a Remmingtom 742 in a 30.06 when I went for my first hunt ever and it was a Moose hunt up near Mt.Edzisa, a group of us were hiking a few miles away from our base camp when we came across a group of a dozen moose that the young moose that caught attention when they were playing led us to the rest.
They were all laying down for the afternoon when we krept up on to a large boulder (30' H - 50' W) that was just stuck in the middle of this large opening near a pond/swamp, a great vantage point indeed.
So being it was my first hunt I had the honours of the first kill I was told, so I got into a good position for a 100 yard shot and had choosen the biggest bad boy in the crowd, set the crosshairs on the back of his neck (as he was facing away from me) and for some reason he got up turned broadside for me and at the same time his head turned and he just looked straight at me, so I repositioned my crosshairs quickly to the heart and lungs area, and opened fire, now somehow I thought that I only pulled the trigger twice, but there were no more rounds in the magazine, I had shot five rounds thinking that I only pulled twice, the moose was in rough shape, probably wasn't going to far but was still limping away towards the pond/marsh, I looked over at the others and nodded to Mr.338WM next to me and he put the finishing shot into the hump, right there and then I gained a whole lot of respect for the 338.
I was glad that I didn't have to go into the water for retrieval of that monster.
The other moose in the group must not have seen much of man as they all just stood there wondering what the hell just happened and once a couple of them noticed that the big was twitching a bit on the ground, they simply mosied on away in no particular hurry.
So it is just now that I am adding a 340Wby Mag to my collection, more for the heck of it, and the 340Wby Mag just to out do the 338WM a little bit.
I have seen plenty of 7MM Rem Mags take a moose at long yardage also, and
the 303's have probably taken down the most (#"s) of big game from all around the World, in it's days of glory before some of these now older cartridges were ever around or just introduced.
I also have a Canadian Centenial (1967) Remmington 742 in 308win that I lent out to a buddy on a moose hunt and he had no problems controlling the shots, unlike me! and put the moose down right next a road from 200yards, one shot. Having the moose 20yards in from a road sure made loading the moose into the truck a sinch, easier than packing pieces a few miles each trip.
I'm sure that with the experiences I have to date, that first moose for me would have probably went down on one shot to the spine/hump with that 742 30.06, but you got to start somewhere.
So there you have it, the caliber game is up to you, lots to choose from but,
I'm voting for the 338. Just Because.