One of the primary reasons to use hollow point ammunition for self defense is to avoid over penetration. There are two reasons for that:
- if the bullet exits the assailant, it poses a threat to innocent bystanders behind the assailant; and
- of much lesser importance, the energy it has upon exit isn’t left in the assailant and is no help in producing rapid incapacitation.
This is a .32 ACP 75 gr cast bullet launched at just 765 fps from a 3.9” Walther PP. It’s about as wimpy as it gets for a center fire pistol cartridge (other than the .25 ACP). However it still delivered 27” of penetration, more than enough to pass through an assailant and tag someone else.
A second primary reason to use hollow points is to dump the energy of the bullet in the assailant and ideally increase the diameter and volume of the permanent wound channel.
At handgun velocities (under about 2000 fps) energy transfer isn’t a huge deal as the resulting temporary stretch cavity isn’t usually large enough to cause permanent tissue damage.
Which makes the diameter and volume of the wound channel even more important. Rapid incapacitation occurs due to a cardio vascular hit that results in rapid loss of blood pressure. Larger wound channels increase the potential for that to happen. Rapid incapacitation also occurs with a hit to the central nervous system; the brain and the large nerves in the spinal column.
Even with good bullet placement, drilling smaller holes with non expanding bullets decreases the odds of both.
Finally, a couple effective hits with hollow points is both more effective at achieving rapid incapacitation and is arguably less lethal than a larger number of hits with non expanding bullets.
For example, hitting an assailant center of mass with 10 rounds of .22 LR will almost certainly be lethal as all those wound tracks will damage multiple organs and compromise multiple systems which increases the risk of the assailant dying before a surgeon can repair all the damage.
The same is true for 4-5 hits with 9mm FMJ.
Neither of those however are very effective at achieving rapid incapacitation and short of that, the wounded assailant could very well kill you before he succumbs to his or her wounds.
I worked a case with a thoracic surgeon from South Africa once and between his military experience and time spent in an NYC hospital he had worked on about 1500 patients with gun shot wounds to the chest. He told me that based on his experience the most lethal handgun round was the .45 230 gr FMJ, followed by 9mm FMJ.
He also noted the more times a person is hit the more likely they are to die for the reasons I stated above; multiple wounds tracks and multiple organs and systems compromised.
The key words here are “most lethal” and “in his experience” (as a surgeon in an operating room). In order to get to his operating room, the victim had to live long enough to get there. That restricted his sample of gunshot victims to those that survive long enough to be operated on. Of those, patients shot with 1-2 hollow points were more likely to survive than patients shot with multiple FMJs, and patients shot with FMJs were more likely to be shot multiple times before they stopped the assault.
——
As a practical matter it often doesn’t make much difference whether someone is using FMJs or hollow points as many hollow points don’t perform well in a particular handgun as they don’t achieve enough velocity to expand, particularly in short barrels. When they fail to expand they perform just like an FMJ.
Under penetration can also be an issue and it can hinge on fairly small differences in velocity. Below we have an 8” difference in penetration with the same load from 4” and 3.15” barrels, with the longer barrel in this case producing inadequate penetration with just 70 fps more velocity as this particular bullet has a very narrow effective performance envelope.
In contrast, here we have the same 124 gr Sig V-Crown bullet and the same load producing varying but still acceptable expansion in three significantly different barrel lengths with all three of them producing between 14” penetration (1351 fps from an 8.9” MP5) and 18” penetration (1015 fps from a 3.15” Micro 9). In this case the bullet has a very wide effective performance envelope.
—-
Range ammo will almost always be better than a poke with a sharp stick, but a good performing hollow point will be preferable, and absent under penetration is always a safer bet. You just have to do enough research or your own testing to be able to determine whether it will be effective at the velocities achieved in your handgun.