I was invited on a Nilgai hunt in Texas, but the outfitter's website said:
"Check your firepower. Having plenty of guns is important, and many Nilgai hunting operations have a minimum caliber requirement of a .300 magnum. Optimal calibers like .338 – .375 are perfect."
https://303ranch.com/texas-nilgai-hunting/
I hunt with a .308, so I passed on that trip.