As I've posted many times before;
Any 55gr PtSpt or heavier.
Well placed shot. This includes heart/lung shot.
Favorite loads: (I don't use factory ammo, but these will closely mimic my handloads)
1. Hornady 60gr SoftPoint (I saw these at Academy Sports in Opelika,Al last week!) I load them over 26.5gr of either BLC2 or RL15 in .223; 38.0gr of H380 in .22-250. (duplicates the performance of .243 w/100gr Hornady BTSP).
2. Winchester 64gr Pt.Spt. (I use the Sierra 63gr in my .22-250, 65gr BTSP in the .223 which has a faster twist)
3. Hornady 55gr PtSpt. (I use 27.2gr of BLC2 for 3,100fps from 18.5"bbl)
I've had more blow-ups and failure to penetrate with a .243 than either .223 or .22-250 due to the .22's being constructed not to "come apart in flight" from the ultra-fast .22cf's.
Just my observations from 40yrs as a hunter and 30yrs as a Game Warden.........