I wanted to use my 454 Casull on my most recent Giraffe hunt, but as I was traveling to the South African location from my work in Angola, I was forced to use the weapons provided by the PH, as I have done on multiple trips with good success. There is no doubt in my mind that the 360 grain Buffalo Bore hard cast loads from the big revolver will do the trick in fine fashion if the shot is properly placed, but so far the largest animal that I have taken was a 1000 pound moose.
I have taken 3 mature giraffe bulls in the past. The first one I head shot with a 30.06. The second one was taken with a shoulder shot from a 416 Rigby, and the last one I killed with a crossbow. The crossbow kill was the most impressive and satisfying, as the bull only ran a very short distance after being hit dead center in the shoulder from a broadside position. It was a great experience that has pushed me further towards getting my own crossbow, but I can't decide which one to buy yet.
From what I have seen and heard, a giraffe isn't all that hard to take down with the right projectile and good shot placement, but if you shoot one poorly you are likely in for a very long day. Those long legs can cover a lot of ground in a short time!