I have only ever shot a couple of animals with the 243, since I own and prefer the 6mm Remington.
The difference between the 2 chamberings is largely insignificant. [100-150 fps with a 100 grain Partition]
I do not recommend these 24 bores for moose hunting, but they are excellent deer, black bear chamberings.
That being said, I have shot a couple of moose with the 6mm, and it worked just fine. Shot placement being paramount.
In the hands of a cool, collected individual who can hold his fire on a less-than-ideal presentation, it will work.
Regards, Dave.