shaman,
I can assure you that I'm familiar with how high a bullet exits on the side of an animal affecting the size of the blood trail. In both the instances I mentioned, the hole was about a third of the way up from the bottom of the chest. Not only were both entrance and exit holes tiny, but the narrow wound channel didn't result in much interior damage. The vast majority of the blood remained inside the undamaged portions of the lungs, which were considerable.
Bullets that fail to open are certainly rarer than bullets that fail to penetrate, but the make of bullet that failed to open on the pronghorn buck is actually pretty popular, even though failures to open have been documented by quite a few hunters. Sometimes the bullet is even recovered, normally through a severely angling shot on a larger animal, providing further proof of the problem. But this normally occurs within a fairly narrow range of bullet weights and diameters, one reason many hunters never encounter the problem when using this particular bullet.
The other problem is that most bullets even in that narrow "problem range" expand fine. Between those two factors, most hunters will never encounter a bullet that doesn't open, because most hunters don't see many animals killed. But when it does happen problems can definitely occur. One of my good friends once had two of that brand of bullet fail to open during a safari in Africa, resulting in very long chases. Luckily, both animals were recovered--and both bullets were recovered. One had barely started to open, but the front end never expanded even to full bullet diameter. The other didn't open at all.
