There are a lot of factors involved in shooting a giraffe. The first one I shot was a large mature Bull, who had an attitude and it already hurt a couple of locals on a bicycle the day before and was pretty much beating up every female in the herd and it chased off the only other bulls in the area.. even chased our hunting truck down the road and when he turned and looked at us, he was clearly on the hunt for trouble. I put four rounds in him out of 470 nitro express double rifle from 50 yards to as close as 20 yards and it was like I was shooting him with the BB gun until he finally wobbled and dropped dead. All 4rds were good hits in the vitals with500gr Aframes.
So leave your 6.5 Creedmoor and your small calibers at home when it comes to dealing with a giraffe who has pumped full of testosterone and adrenaline you might get away with it otherwise but not in that scenario.