For example, one of the most popular self-defense rounds, the 9mm hst, has been found to penetrate deeper and more reliably with the standard loading rather than the plus p. The faster you push a round, sometimes the more shallow the penetration.
Just to clarify,
For expanding rounds; yes. Typically, higher velocities cause the rounds to expand rapidly, which tends to decrease penetration.
For non-expanding rounds, like FMJ or Hardcast lead, higher velocities don’t reduce penetration.
One of the interesting tests, was using HST bullets loaded for full power 10mm (vs the downloaded/lightly loaded factory 10mm HST). Testing in ballistics gel showed that the bullet isn’t constructed for those higher velocities.
As the round expanded violently at the higher velocities, the petals either folded back (reducing their effectiveness), or broke off.
Interestingly, videos of ballistics gel testing of Underwood’s full power 10mm XTP loads, showed that those older design bullets performed better. The older design bullets typically don’t expand as well as the newer design HST,
at lower velocities, but at the higher velocities of full power 10mm loadings, they expand better (similar to newer JHPs at lower velocities), while holding together and penetrating quite well.
I have seen the claim that a headshot on a bear will frequently deflect off of the thick skull. I haven't tried it myself. Conventional wisdom is to aim for the heart box,
This is one of those things where knowledge of the anatomy is important. Most people would instinctively aim between the eyes (or higher) for a headshot, which will very likely result in what you’ve mentioned, as a bear’s skull is both thick, and sloped at a steep angle.
When attempting a headshot at a bear facing the shooter, the advice is to shoot it up the nose, as that shot will reach the brain, both due to the location of the brain (lower than expected, compared to humans), and avoiding potential deflection.
In reality, especially with an attacking bear, the average person is simply going to be directing fire anywhere in the general direction of the bear
*** if you happen to fall over while backpedaling and shooting, try not to shoot your own feet. This has actually happened in more than one bear attack incident.
Charging bears are scary fast
*** no injuries in the video. The camera was setup remotely on a tripod to capture the bear’s release. Grouchy bear attacked it anyway.