I would say that , assuming they were witin reasonable range of your skill ability, and draw weight, you probably shot too high and forward. Resulting in perhaps clipping the front of the lungs and very little to no blood in the first 50 yards or so. remember to go though a system and not to take a shot unless you are sure it is a kill. And check out a deers anatomy some time. I lost one this year for that very reason, mine was a pass though of the blades, but was too high/forward. I felt bad, because I new it was more than likely dead, but learned a little. it was the first deer i ever lost. Which sucked. But keep your head up, and goodness dont shoot them shoulders man!!!