He took off bounding? You mean he ran away like nothing was worng, jumping and stuff? If thats the case you eliminate and kind of leg shot or I would even say a muscle shot. You said you tracked him 50 yards. Well if you took out the top of his lungs, and he was running, i could see him going 100+ yards. The chunks of blood ( most likely clots) sounds like a hit in the vitals. I think in the morning if you do a grid search you will find him. Those huge spotlights can actually make it very hard to pick up small amounts of blood. Take it slow and be careful so as not to rush in and disturb any sign thats there.