I think I'll ask you the reverse of your question. Why do you use such puny calibers for your hunting, isn't that underkill?

Many places have outlawed the use of .22 cal on deer sized and larger game animals...the reason, too many crippled animals.

I expect that you use your .223 for varmints and your .243 for where deer and antelope play...absolutely nothing wrong with that...thousands have done the exact same thing...I sometimes, actually mostly, use a 6.5 X 55 for deer.

The term knock down power comes to play here. Would you take a shot at a 240 point/14 count deer, standing nearly, not quite butt/rear/tail end facing you...the only shot you've got--though some very light brush--with your .243. shooting for the bullet to travel the length of the body, from just ahead of the rear leg, behind the rib cage to the chest...You could shoot but the bullet would never reach any of the vital organs...someone shooting a .300 would make it...a .338 has a much better chance..and with a .375, no problem...but the impact of the bullet upon the nervous system, with a heavier bullet would, using a writer's term, cement him right there, probably, wouldn't take but a few steps (staggering) and go down. Surprisingly there is little meat damage but the internal organs are sure a mess.

I was hunting moose with a buddy who was using a .340 or a .378 Weatherby--can't remember which--and placed seven (7) shots, yes 7 shots, his last 7, through the heart/lung area of a standing broad side moose at about 120 yards distance. The beastie kept on eating for about 15 minutes, took a few steps and dropped.

I was using a Browning BLR in .358 Win Mag and met my moose at about 90 yards, placed one round in the heart/lung area, he trotted about 25 yards and piled up.

A First Nations (Indian) fiend of mine, canoed to about 20 yards from his moose and placed one in the brain. The moose grunted, took a step and keeled over. He was shot with a .22 LR standard velocity solid point--highly illegal, by the way.

What I'm saying is that there is good or bad stories, confirming or denying the greatness or lameness, of either small, very fast bullets or slow, big bullets.

But we shouldn't cast aspersions on our fellow hunters/shooters just because they are using something different than us. We have enough problems and hassles from the anti gun/hunting people as it is! Why add more? Why add more fuel for themto flame? Give them something to divide us! Make their stand more powerful!