I feel like this thread is gonna turn into a real flame war, but lets see if people can be mature.
I lost 2 deer, both with a gun.
One was a high spike, the first deer I ever took a shot at, I was 16 I think. It was facing right towards me about 50 yards away. I shot right in the center of his chest and he fell over turned around got up and took off. My father was hunting several hundred yards away and came over about 15 minutes later to see if it was me who shot. He said he kicked up a deer that was laying down and there was a 6 inch pool of blood where it was. We went back to the spot where he jumped the deer. We wanted to wait to track, but it was about an hour and a half before dark, and just started snowing/raining heavily as well. We heard that we kicked this deer up another 2 times before it ran into private property. We asked the land owners that night for permission to search for it the next morning and they granted it. We searched for hours and hours, unfortunately we never recovered him.
The second deer was a monster buck. Long story short, I only found a few drops of blood from him, and he never stopped running for a couple miles before I lost the tracks in the snow.