There are lots of folks that use a .243 and do well with elk. A guy I knew almost 20 years ago hunted with nothing else, and had 13 sets of elk horns on the wall of his den.
The only one he ever lost was when taking a shot he had promised himself he would never take - the elk was moving in the timber, but it was so close he couldn't pass up the shot. He felt he hit the animal, but a light rain washed away any hope of finding a blood trail and night was coming on fast. Extensive searching the next day revealed nothing.
Now, the bullet could have hit a branch and deflected off, or the elk could have done what elk are known to do - soak up lead and walk off with no indication that they were ever hit. But he still kicks himself for pulling the trigger when he knew he shouldn't have - and in all seriousness, the same thing could have happened with any cartridge.
Grits Gresham wrote that Whiskey Chamberlain had 15 one-shot kills on elk with a .243.
Years ago I talked to a very experienced Idaho elk guide (named Smith?) who recommended the .243 for anyone who couldn't handle more powerful cartridges because his experience showed it worked, and worked well. He set up his wife with a .243 when she shot her first elk - a one-shot kill. His only cautionary words were not to shoot much farther than 300 yards and to wait for a good shot...good advice for any hunter with any firearm.
I believe alpinecrick from right here on the 'fire has written many times of the efficacy of the .243, and has solid experience using it and the Nosler Partition against elk.
Another well-respected contributor to this forum related how Gail Root, the Nosler technician, designed the 95gr Ballistic Tip to be a big-game bullet, and used nothing else on numerous big bulls.
I think there are numerous cartridges that are better suited for elk, but success speaks with a loud voice - and the .243 is enough.
