In my experience the best blood trails come from full penetration with exits from hits at the mid line or lower and especially when the bullets are relatively low in their velocity.
My old friend Cy Moorhead, a trauma surgeon in Korea and Vietnam and also as a civilian doctor with over 30 years of practice explained it to me. He said the platelets in the blood are released instantly when red blood cells are ruptured by the attempts to compress the liquid. Liquids can't be compressed, but the semi-solids can be, so they rupture. The process turns part of the blood into a substance called fibrin which is what causes clotting.
Hits with bullets over about 2600 FPS do this instantly to the blood, and that why we see the:"jello" on the inside when we dress the game. Low velocity hits don't do it to the extreme that high velocity hits do. Blades don't rupture the cells at all and the process of clotting is much slower with deep cuts than it is with high velocity bullets. Bullets do a lot of damage to organs around the wound because if the shock they produce, which we don't see with blades, but nothing bleeds more freely then a cut with a blade.
Back to bullet wounds:
So the shock we see from the magnums is not as pronounced in the mid velocity hits. Real high velocity rounds tend to drop game in their tracks most times if your bullet doesn't fail, but there are always a percentage that seem to run off, and run farther then those hit with the older rounds that throw bullets at around 2500 FPS (which strike at even lower speeds) and give exits. Cy told me as a man with 50+ years as a hunter and also a surgeon with a 47 year long job before he retired, hits with projectiles that impact at 2100 FPS and lower bleed out a lot more then those that clot fast from the dump of fibrin due to hydrostatic shock from hits at 2600 and faster. Heavy pistol bullets cause bleeds that seem very voluminous, with blood trails looking like they come from a hose. The reason is that the hits don't rupture any red-blood cells due to hydrostatic compression so fibrin is formed too slow to stop the blood flow.
Looking back on my 50+ years of killing game and seeing game killed, I see what he was talking about. But I have seen some weird performances with mid velocity hits a few times too, so there are no formulas that are without exception.
Kills on game with large bullets from "slow rounds" like 8X57s with 170-180 grain bullets, 300 Savage with 180s grains, 35 Reminton with 200 grains, 303 Brit with 180s, 30-40 Krag with 220s, 30-06 with 220s, 45-70s with cast bullets, 44 magnums with hard cast flat point bullets ---and so on.........all seem too be extremely deadly with chest hits and yet many times the game runs a short distance after such hits, leaving a blood trail a blind man could follow. But such runs are very common and they are short because the game bleeds out REAL fast and can't go very far.
Kills with fast rounds like 270 with 130 grains, 30-06 with 150s grains 7MM mags with 140-150 grains, 300 mags with 150 and 165 grain and so on, usually drop game almost instantly about 90-95% of the time, but when you get to the last percentage, the ones that run..........they can and sometimes do run a long ways. The reason is the bullet caused it's one clotting and the brain is not cut off from blood pressure as fast as those that lost all the blood in the body cavity and on the ground.
Those hit with super fast bullets that break up can add another factor. Wounds that sometimes don't go very deep or that turn off-line to an extent you don't hit the things inside you wanted to hit, and/or do as much damage as you intended.
But these observations are generalities, not immutable laws.
I have seen low velocity bullet do weird things a few times and I have seen very poorly made bullet kill like lightning. But in general trends what Cy told me is consistent with most of the kills I have seen in my 56 years of killing game.
