Disclaimer: My experience with a .243 was with middle TN deer that I'd guess would be considered mid sized.
I started with a Marlin 30-30, then a Remington 700 Classic .270, then in '85 got a Ruger .243RL, their ultra light. For 13 seasons or so I guess I killed 30+ deer with that .243 and nothing dropped them faster. 42grs of IMR 4350 and a 100gr Nosler Partition did the trick. At 75yds or less the bullet didn't exit, the deer ate about 2,000 #'s of energy. The few deer I shot over that range did exit, and all but one dropped in their tracks. I had exactly
one deer run 100yds, a doe I bullseyed at 85 yds and when she collapsed guess where it was...right under my treestand! I mean literally right under me. I even took a pic of it from my stand. No other deer went more that 40yds if that.
I shot 2 coyotes with it. The 2nd was at 150 yds and it knocked him over a gentle rise. When I went for him his left front foot was impaled on his canine tooth and I dragged him back to my truck for gutting by his leg with the foot still impaled. The guy I was with couldn't believe it, but he was there :wink:
All those deer were one shot kills, though I did gut shoot a nice little buck that got away. He would have with my .270 as well. I made a bad shot and felt terrible about it. Only deer I ever lost...
Sure the .243 has its limitations. The 2nd deer I ever killed was walking dead away from me and didn't look like he was changing directions anytime soon so I drilled him a-hole to appetite with my .270 and recovered the bullet under the hide in his neck. I wouldn't have taken that shot with a .243 as I would have tried to shoot him in the back of the neck instead. Can you believe I was worried about ruining the mount?
Bought my boy a Rem. Youth .243, but we never hunted with it. Both our .243's would do about 1 1/2" or less at 100yds. for 3 shots. I was happy with that and didn't try to tweek it any. I'm certain I could have shrunk that a bit if I tried.
There's always going to be controversy over the .243. Know its limitations, it's not a 300 Win Mag! Any rifle from a reputable manufacturer should do just fine. Bullet choice is crucial! The 100gr Nosler Partitions worked great for me. If you don't handload you can buy them commercially loaded. I was going to try out the Barnes solid copper bullets that run a bit lighter and shot great, but I never got to hunt with them.
That's my story and I'm stickin' to it no matter what anyone else says. Oh, and before I forget, of the 30 or so deer I shot with my .243 I believe only 2 or 3 were does. I don't want anybody to think I was shootin' fawns or something...