I believe that the physical attitude of the game animal has a lot to do with which cartridge will be adequate and which will be a better or best choice. Where nilgai are rarely hunted and not pressured or chased a good bullet in any caliber capable to killing a 500 pound animals will do quite nicely on a calm animal. I used a .338 Win. mag. simply because I shoot it well, overkill is a myth and I had a lot of 250 grain Grand Slam bullets that I wanted an excuse to use for practice and my hunt. As long as one puts the bullet in the proper place, at a reasonable hunting range and the bullet is well constructed with a higher SD I see no reason to shy away from anything in that 30-06 ballpark. And that park is quite crowded.
