I don't know how that can be verified, but from my experience shooting a half dozen moose, and present when several others were taken by friends, I wouldn't go any less than a 270, and even that cartridge may be not enough gun in certain situations. I've heard that banter that "I know a guy that shot one with mighty mite xyz" and I'm sure it can and has been done, but when you want a quick clean kill and minimize the possibility of your moose running into a swamp to expire, I would recommend the 30 calibers and upwards.
If I was backing up my wife and she had a 6.5cm with 140 partitions, I would be fine with that. I watched one shot last year with a 7-08 at 200+ yds as I was present with a bigger gun.
Then again, shot placement is key, but couple that with a well built bullet and appropriate caliber to get the job done.
I was part of a hunt years ago and watched a yo-yo from out of state shoot a 50+ incher with his 300rum, hit it in the hump and dropped it. He ran up to celebrate and said moose not only got to its feet but was determined to make him a permanent fixture in the tundra. As it charged him he fumbled for his rifle, stumbled over backwards and got one shot from the hip hitting the moose in the nose and turning it away. What ensued next was a firefight the likes of a military conflict that has been part of many campfire stories since.
Lots of good info here from guys way more experienced than I, but I think we are all on the same page more or less.
For the most part moose aren't hard to kill, but I wouldn't want to be the exception to that with a marginal hit using a marginal caliber shooting a marginal bullet. You can be sure those stories never make it on the internet bragging boards.