I am no bullet or ballistics expert by any means. I just go by trial and error of myself and others that I trust. Then add a little common sense on top to boot.
Now with that said......If that 340 gr Hornady bullet broke apart that bad being shot into water just imagine what would happen if you hit an elk's rib. Years back, I deer hunted for one year with the .54 cal 348 Gr Powerbelts. Thinking the extra weight would make a difference. That bullet exploded when it hit bone and did not penetrate well at all. I helped plenty of buddies track deer that were shot with 295 Powerbelts several decades ago. Most were broadside shots that hit rib or shoulder. The Powerbelts would typically grenade. On the tracking trail we would find blood and bone chips. We were about 50/50 on recovery due to lack of penetration.
Now I don't want to sound like I am bashing Hornady. They are by far my favorite ammo company and I was excited for the release of this new 340 gr BoreDriver ML bullet. However I wouldn't even consider this new bullet for deer hunting let alone elk hunting.