late to the battle but did not find the specific study.I read an online scientific veterinarian report that published the results of hydros tested in the euthanasia of beached whales in New Zealand and Australia. They used .30cal hydros in a .308 Win, .30/06 Spr and a .300 Win to head shoot beached whales. The hydros proved they all had exceptional straight line penetrative power.
If interested, use the search engine - cetaceans euthanasia - to find it.