You see a lot of articles about testing bullets in ballistic gelatin, using it as a simulacrum of human tissue. It's not an ideal medium from which to extrapolate bullet performance in human flesh, because flesh differs in density (e.g. fat, muscle tissue, internal organs, etc.); and bones are much harder to penetrate than flesh, but this factor isn't present in ballistic gelatin. Nevertheless, gelatin is a worthwhile medium to compare bullet performance against other bullets. Its uniform consistency, and the ability to place barriers between the firearm and the gelatin, means that we can compare offerings from different manufacturers to see how they perform.
Sometimes the results are surprising, and tend to disprove a lot of manufacturer hype. Greg Ellifritz published an interesting article last week in which he compared bullet performance from small 'mouse gun' pocket pistols and revolvers - and found almost all of them wanting.
You’ll notice that I didn’t provide any expansion data. That’s because NONE of the .380 or .38 special rounds expanded at all! All of the bullets except for the two 9mm rounds could have been reloaded and fired. They had no expansion whatsoever.
. . .
Many knowledgeable handgun instructors have noted that there really isn’t much significant difference in stopping power between most of the rounds people shoot at criminals. Is there any wonder? Look at the .38 and .380 rounds we tested. All penetrated the same distance and remained .35 caliber. Bullets with identical performance in gelatin should have similar performance in human bodies as well. It just doesn’t make much difference what round you carry in your “mouse guns.”
. . .
The bottom line learning point for me was that one should not rely on a bullet’s expansion out of a short barreled pistol. When shot through clothing, all the bullets remained remarkably unchanged with no expansion whatsoever and penetrated to a similar depth.
There's more at the link. (I noted much the same thing in two articles published earlier this year, which also make interesting reading. Mr. Ellifritz's article confirms my thinking on the ammunition recommendations I made in the second of those articles.)
A few days later, Mr. Ellifritz published an even more interesting article, this one comparing defensive ammunition performance in hog tissue. Here's an excerpt.
The human body is not a consistent medium. Muscle, fat, organ, and bone all have different mass, density, hardness, and flexibility. In general, a bullet will penetrate much deeper in gelatin that it will in human flesh.
The primary reason for the diminished penetration in an actual body is the presence of skin and bone.
Skin is very elastic. A bullet uses up a lot of energy stretching the skin before the skin actually breaks. Most ballistic experts believe that the skin itself is equal to one to two inches of gelatin penetration.
Bones also tremendously slow bullets and limit their penetration.
We want a bullet that penetrates 12″-18″ of gelatin. That translates to roughly 6″-10″ of human flesh, depending on the structures hit.
. . .
Ten days ago, I participated in a ballistic laboratory of a different sort at the Paul-E-Palooza Memorial Training Conference. Instead of shooting gelatin, we shot (dead) pigs instead. It gave us the ability to actually see how bullets performed in real flesh and bone.
Keep in mind, all of the pigs were less than twelve inches across. Every load tested penetrates deeper than twelve inches in gelatin. How many rounds do you think penetrated through and through on the pigs?
If you guessed NONE you would be correct. Not a single round (including the rifle and shotgun rounds) fully penetrated the pigs. Most wound channels were six to eight inches deep. Those that hit larger bones terminated even earlier.
Again, more at the link. Highly recommended reading.
I continue to recommend a larger, heavier-caliber handgun as a better defensive platform than a small 'mouse gun' or pocket pistol. It's worth the extra effort to 'dress around the gun' to carry it concealed, in exchange for the better performance available from it. Larger handguns are typically easier to control, hold more ammunition (an important consideration when multiple attackers and/or mob violence may be a factor), and fire a more effective round. (Shotguns and rifles are even better performers, but they're a bit difficult to carry concealed!)
I'll continue to carry small pocket pistols and revolvers, but almost always as a backup to a larger primary weapon. I'll also load them in accordance with my earlier recommendations, to maximize their effectiveness in a defensive situation.