Ditto CW, anything can happen to any product, but the overwhelming majority of evidence says that these bullets are extremely effective on Whitetail deer. I have shot quite a few deer with 270 core lockts, all with the same predictable performance, usually found just under the skin on the far side of the deer if shot in the shoulder or a pass through with a good exit wound. BTW whitetail deer are tough, but as far as big game goes, I don't know of any smaller framed thinner skinned animal that is considered "big game" than whitetailed deer. Especially here in the southern half of Texas, deer have thin skin, lean meat, and thin fur, that can allow a slighty defective bullet to fail to expand although this has never happened to me on some pretty small bodied deer.