They are one of few calibers permitted in killing whales by Native Americans.
That is what passes for a native hunt today. Whales that spend years peacefully being watched by boats along the coast, are protected, interact with friendly people, then surface near these natives and are in for a surprise.
When following the rules power boats transport them to the whale location, then they get into canoes and go after it. It is shot with modern harpoon guns with lines attached to large floats. Then they shoot at the whale a few times with something like the .50 BMG.
This is permitted under special exemption for certain native tribes who get an annual whale limit.
Of course that is when things are done as allowed and work out.
They don't always succeed in easily killing the whale:
First, they harpooned the whale four times. Then they shot it 16 times, possibly more, from at least one of three high-powered, large-caliber rifles, including one nicknamed "Tyrannosaurus."
The California gray whale lived for 12 hours before sinking to its death in 700 feet of water off Neah Bay.
They got prosecuted for actually doing the shooting from power boats when not allowed.
According to the indictment, Noel, then a member of the tribe's Whaling Commission, checked out three guns from the tribe for what he called "practice:" A .50-caliber rifle, a .460- caliber Weatherby rifle and a .577-caliber rifle, the gun the Makah call "Tyrannosaurus."
Although the whale's body has not resurfaced, prosecutors said shell casings and witnesses' accounts show that the men fired 16 to 18 rounds. Oesterle also pointed to a photo of bullet wounds lodged in the captured whale.
The ".50-caliber rifle" of the article is the .50 BMG, as the rifles kept on hand for whale shooting must be in .458 Winchester Magnum, .460 Weatherby Magnum, .50 BMG, or .577 Tyrannosaur as those are the permitted whale shooting calibers.
Obviously shot placement even with the .50 BMG is important when slaughtering whales.