FWIW, my theory on how to get a good blood trail is first to use a bullet that'll give a pass through, after tearing up the innards, and also to keep shot placement below the half-way point on the chest, well below in fact. I try to hit the top of the heart. A higher hit means more blood has to accumulate before it can leak out the holes, and even then it must run down the side through the hair before it drips to the ground. A heart shot starts leaving sign very quickly. One doe I actually hit too low with a 150gr .308 NP, just above the sternum, still had her heart shattered by the fragments and made it maybe 20 yards. Deer shot high through the lungs can go far, leaving very little sign, sometimes almost none. A deer with no heart, or with the heart disconnected from the major blood vessels can only travel as far as the oxygen in its muscles will allow; that's my story and I'm sticking to it.
