For what it's worth, Zayne Van Der Merwe of Zambezi hunters uses a Merkel double (probably a .470) when hunting elephant. I've seen him twice now on Versus' "Dangerous Game" series of tv shows. Both times, he was hunting with a client carrying a bolt. One of the clients was a PH in another part of Africa who speciallizes in bird hunting, and the other was just a regular American dude. Zayne and the birdhunting client got charged: client shot first quickly followed by Zayne (frontal brain shots that missed); upon Zayne's first shot, the bull stumbled some. Then one of the trackers fired, one more from the client, and another from Zayne, finished by an insurance shot from the client. Pretty decent TV, given what's normally on.

Anyway, at least one DG hunter uses a double, and is on TV with it once in a while.