Fairly old saying but it applies very well here. Can a .243 take an animal in the Moose weight class? Most certainly yes. So will a .22 short if put in the perfect spot under perfect conditions. Should one rely on a .243 to efficiently take a Moose? Most certainly not. Just how often does one get that perfect shot presentation where a .243 would work well? Moose hunting for most people is an expensive proposition and not one I would want to bet that large expenditure on a small caliber rifle. You don't need a cannon for Moose. You don't even need a magnum. What you do need is a good amount of bullet weight with enough power behind that weight to bust through a very large amount of hide, muscle, and heavy bone. I can honestly see a rib bone of an adult bull Moose turning a .243 caliber bullet so even that perfect broadside presentation could easily turn into a very long day of tracking a wounded bull. And if you have never been up close to an adult bull Moose you aren't ready for that. They are a very large animal and highly dangerous. Even a smaller cow is 5 times the average adult human male's weight and can kill you in the blink of an eye. Only the largest and hungriest of Brown Bears will mess with an adult bull Moose. That ought to tell you something.