I am not saying the 243 will not kill deer , it just dose not have enough energy/penertation for the poor shots that some "hunter" are willing to take. If you pass up the marginal shots it will do good but if you try to penertrate to the lungs from a ass shot you may lose the deer . I know the 243 will kill deer even moose but the 243 is ill suited for moose if you have to break bones,I use a 257 Roberts AI on deer and the 7-08 or larger is what I would use on moose.
My distaste for the the 243 came from tracking 2 deer that were wounded with the 243 ,1 was a shot square on the shoulder joint broke the shoulder but failed to penerate worng bullet ? maybe
The othe was a texas heart shot that failed to penerate to the lungs .
Also a 243 bullet hole has failed to leave a good blood trail several times on a fat deer if there is no exit hole.