Everything I have read regarding the Game King is they perform well. Sorry to hear you had a bad experience. It could be that you got a batch that was mislabeled or a batch that was not up to par. How fast was your load at the muzzle?
I use to do hand loads for a person I know, and I used Sierra Game King bullets as they grouped the best. Multiple whitetail deer (bucks and does) were shot, and every deer shot was DRT. It did not matter if the deer was standing still or running away. Distances were from very close to about 200 yards. It helped that this hunter always had good shot placement. This person moved away so I no longer do loads for them.