A few different complaints in the thread. To summarize:
-The shot is too far (I agree, just get closer, that applies if it was a 22PRC or a 50BMG)
-.243 is too weak. I don't agree, all things being equal, those 6mm bullets, the heavy 105gr ELD-X bullets will certainly penetrate.
-There wasn't sufficient energy at those distances. Again, I prefer closer shots, but I'm not convinced the lethality of the 243win with a 105gr at 600 yards is that different than a 7x57 or a 6.5CM. I lump them all together thinking it should have been a closer shot as others have suggested, but energy vs penetration is a tricky thing. I'd take less energy and a better bullet with a higher BC any day. (e.g. I'd prefer her 243 setup to a 7x57 with a 175gr on a perfect broadside where there is insufficient energy for either)