You lost me at .243 loaded with Core un-Lokt on anything above a white tail at short range. I'm going to need a premium bullet. You have to have some minimum level of energy to effect penetration. It can't all be about placement, which seems to be the sunny day song of the undergunned when they optimistically take on larger game. About 1200 ft-lbs at 275 yards is what that bullet had on it. Was it DRT or did it run a ways?
I used to hunt deer with a .30-06 loaded with 125 gr Core Lokt. Worked really well until I exceeded 150 yards. Then it didn't work as well anymore. Despite having 1700 ft-lbs at 200 yards it was a poor design that didn't hold together.
Arrows kill by hemorrhaging. Bullets kill by penetration destroying vital organs, interrupting the CNS and energy imparted creating expansive temporary and permanent wound cavities interrupting the circulatory system.
A lot to unpack there... Yes, the MD was DRT as they say. More by placement than cartridge, high shoulder shot. A 62 gr. Fusion out of a .223 would have had the same result, as would a 200 gr. from a 300 WM. A 100 gr. Core-lokt is plenty for deer. Placement is #1 even with larger cartridges on smaller game, to suggest otherwise is silly. I’d take a 100 gr. .243 over. 125 gr. .308 bullet for deer any day. SD and a bullet designed more for big game hunting. Some 125 gr. .bullets in .308 are designed to do exactly what you described, open fast. You should have picked a better tool for that task IMO. That’s on you, not that cartridge or bullet. If there is a more useless and overused measure for lethality than foot pounds, I’ve not seen it. Much better is to know your game and bullet design parameters. Keep impact distances with in the velocity range the bullet is designed to perform at, using a bullet reasonably