I've used soft lead for muzzleloaders and WW's for modern pistols both with good results. Deer are easy to kill if you hit them in the right place. In the wrong place a 458 WM wont help you.
My Dad's mentor, a WW1 Vet, swore by the 25-20 as a deer killing machine. He lived in the Hill country and used iron sights only. Pop's favorite was a 22 Mag FMJ and head shots....Yea I know....