A 180 grain bullet should do the job nicely. It is a big animal so you could go bigger but 180 with good shot placement should do the trick and it carries better if you need a little longer shot.
Just don't shoot one on the other side of a drainage, I had a friend do that. He was proud of his 300 yard shot until I told him we would probably have to walk a couple of miles to get to it. And I also told him that was why I didn't take the shot.
It took us 6 hours to get it out. Since he's from the coast, he didn't enjoy it, heck I live at 6000 feet and I didn't enjoy it.
Cum catapultae proscriptae erunt tum soli proscript catapultas habebunt.
When catapults are outlawed, only outlaws will have catapults.