It's just not that hard to hit a 2 ft diameter lung. They sneak up to within 10 yds, fire a full auto burst into the lung, and another as the creature flees. All they need is a for a very few rds to reach a few inches into one lung. The critter coughs up blood, aspirates it into the other lung, drowns in its own blood. The poachers merely have to wait a day, then watch for circling vultures.
So those who insist that one "needs" a heavy rifle, in order to be able to deal with big critters, are simply not aware of how such things are done. It has nothing to do with "fair chase", sportsmanship", etc. It's just done by knowing the animal's weaknesses, and how to properly take advantage of those weaknesses. You can be in a tree stand, in a group of rocks, in a pit, etc, unreachable by the animal, as it bleeds out (in the actually rare event that it does try to kill you, instead of just fleeing at your shot).
Pygmies used to take elephants with spears to the guts, by hiding in pits, thrusting up into the creature from underneath. Those guys had heart, unlike today's "men".