I used a 300 Win Mag with 165gr Hornady Interbonds when I shot my cow Nilgai.She was about 150yds,complete pass through high lung shot,dropped right there.I'd go for a quartering away shot,tight up against the shoulder on the on side,taking out the offside shoulder.This way all your wound channel and bullets energy is directed into it's vital organs.If broadside,take just a little bit of the shoulder on each side.They are grazer,browser feeders.The stomachs are quite large and the vitals are well forward and protected by the shoulders.Get a bullet into the vitals as opposed to the stomach and you should do just fine with any of the larger rifles.Just remember,shot placement is everything.

~Molɔ̀ːn Labé Skýla~
As Bob Hagel would say"You should not use a rifle that will kill an animal when everything goes right; you should use one that will do the job when everything goes wrong."Good words of wisdom...............