When my wife started hunting big game, i bought her a New England Arms single shot in 243 Win. The second day of moose season, she dropped a nice cow with one shot at 30 yards with a 90 grain XFB. Busted a 4" chunk of rib back through the lungs. Dead Moose. She stole my Tikka 30-06 for the next season, and dropped a nice buck at 200 yards with a 150 grain Partition. It went 15 yards before it folded up. A couple years later she dumped a nice bull moose with the ole 06 at 60 yards using a 150 grain TSX, and the bull dropped where it stood.
I have used 165 and 180 Hornady Interloks in both my 3006 and my 300WM. All one shot kills on moose, deer and bear. I have switched to Barnes 168 TSX for both my 06 and 300 Win. They are accurate at the ranges I hunt -- 50 to 250 yards.
My belief is that if you put a bullet of appropriate construction into the vitals, there is no magic. It is just smart shooting. I don't take low percentage shots. And I HATE chasing wounded game.
A 243 is not a moose rifle, but it works good if done right. You don't need a 300 Mag for even the largest deer, but they work fine. My 6.5 SWEDE kills way bigger than the numbers it generates.
Enjoy our sport, and tweak the shooter as much as the hunter.
