I call BS. No way a 77 gr bullet at 1500 ft/sec does more damage than a 100 gr .243 bullet at 2400 ft/sec+ does on a deer (dropped, a high shoulder broadside shot, no fist-sized hole on the other side), or a 150 gr '06 bullet at 2700 ft/sec+ does on a deer (ran 25 yards with destroyed lungs and a torn heart, and a quarter-sized exit hole), or a 52 gr JHP .223 Rem at 3000 ft/sec+ on a coyote (DRT on a frontal chest shot that raked the spine and exited the back at the bottom of the rib cage, no pelt damage). Not buying it. A .223 77 gr bullet at 1500 ft/sec is going to pencil through unless it hits a bone, and at that velocity won't have enough energy to blow up that bone. A spine shot would drop the elk, but anyone who can hit a 3" line consistently at close to 700 yards from a hunting position is holding better than 1/2 MOA.
More likely they carved on those elk with that knife to recover bullets... or they were much closer. And I want to see the misses, and the apparent misses that went off and died out of sight and not recovered. You know they exist, because they exist with bad shots from bigger calibers.
Do I think deer and elk, etc., can be responsibly taken at extended ranges, past 500-600 yards? Yes, With a .223 Remington shooting 77 gr bullets? No. At 287 yards? Pushing it... it took two shots and at least one was a gut shot.
What will a 6mm SAUM or PRC do that a 6.8 Western won't?