As I'm sure you know, a bullet causes damage by deformation when it strikes a target. It basically turns the bullet from a long projectile into a flattened chunk of lead, thus enabling greater tissue damage and trauma to internal organs. A hollowpoint bullet bullet is designed to cause greater damage to an unarmored target. Due to the bullets tip being hollowed out, the round deforms into a larger bullet upon striking the human body, thus it causes much greater damage. Think of it as something the size of a dime passing through you flatways as a egular bullet, vice something the size of a nickel for a hollowpoint. Not exact dimensions, but that should give you an idea. However, due to the hollowpoint's tip being hollowed, the bullet loses strutural integrity, and is not effective against body armor because it lacks the strength to penetrate since it deforms so easily.

That about cover it?

The difference is actually quite a lot bigger than that, though that kind of example gets the point across.

Full metal jacketed pistol ammunition, such as used in militaries, is usually round-nosed (e.g. US M882 9x19mm FMJ), and (obviously) doesn't deform. When such a bullet hits a human at pistol velocities, tissue mostly flows around the bullet and is not ejected sideways at a high velocity. Thanks to the elastic nature of human flesh, the permanent wound cavity is then quite small -- here is an example of the kind of wound cavity a 9x19mm FMJ will cause.

As you know, common pistol calibers in use these days range from 9mm to 11.4mm (.35" to .45"). A hollow point bullet for these calibers can expand to twice that diameter or even more, although for common defense handguns and loadings an increase of about 75% in diameter is more likely (compare with 18% for a nickel over a dime). In addition to increasing the diameter, the deformation drastically changes the shape of the bullet. The flat head of a deformed hollow point bullet will eject tissue out of the bullets way at a much higher velocity, as well as possibly ripping the edges of the wound cavity (some bullets, like this, have been designed with this effect in mind).

The greater diameter and flatter shape together can easily double the diameter of the permanent wound cavity over a FMJ design. This is the main reason why using standard FMJ ammunition in a handgun for defense is a really bad idea. Armor penetration is usually a non-issue here, since most handguns will not penetrate common bullet-resistant body armor types even with FMJ bullets.

Obviously, while creating a greater wound cavity, a hollow point bullet will also penetrate less tissue. This is usually not a problem, since you only need 12-18" (30-45cm) of tissue penetration to bag humans, anything beyond that is largely a waste against unarmored humans. As you can see from the picture of the 9x19mm FMJ shot in gelatin I linked, there's plenty of extra penetration on pistol FMJs -- for another example, here's a .45 ACP FMJ shot into similar calibrated gelatin. In some cases, however, the expansion of a hollow point bullet is too sudden and too extreme and penetration in tissue is not sufficient -- this is a common problem in high-velocity loadings for bullets that are rather light for a particular caliber, such as 115gr +P hollow points for 9x19mm.

I guess I'll take that as a compliment

As to the performance of the subsonic 5.7 round: All I can say is that I'm not a ballistics master, i.e. My technical knowledge on the subject is limited.

It could be that my experience with the sub 5.7 was lucky. Some guys will stay in the fight no matter how much you shoot them, and other guys will drop with only a fleshwound (barring ocular cranial cavity shots, or any shot that severs the spinal column). Basically what I am saying is that shooting people is not as much a science as firearm manufacturers like to say it is. Still a lot has to do with mindset, and the mindset of the target. One of the things than any good tactical training program will teach is that you make yourself stay in the fight. Don't give up because you were hit. This can go a long way.

As I said, I'm not strong on the technical aspects of ballistics. As you said, Raygun, maybe I'm really full of crap , but I just wanted to clarify that my opinion of the sub 5.7 is in no way technical, just opinion.

btw: That apology wasn't neccessary, but I still appreciate it. I've got nothing but respect for anyone who can possess the amount of knowledge on a given subject as you do.

That's definitely true. Statistically speaking, it would appear that people are stopped (though not necessarily killed) by relatively minor .22 LR hits more often than from any other type of round, ostensibly with their disposition at the time being the major factor. Obviously that's something that ballisticians and firearm manufacturers can't factor in as a design variable. From their perspective, it's all purely mechanical.

How much can you tell us about the particular experiences you've had with the 5.7x28mm subsonic? Has your opinion been gained over several instances, or was it one particular incident that made you think so highly of it? What were the circumstances? I would suppose you are comparing it to the 9mm PAMAS G1, which I know you do not have a very high opinion of...

In that article I mentioned from David Fortier (in G&A's recent Combat Arms issue), he mentions during a brief run down of the terminal ballistics issues, that the P90 "was utilized in the raid on the Japanese Embassy during the Lima, Peru incident. In this case the terrorist leader was killed by one round fired from a suppressed P90, which penetrated his vest." He doesn't say which load was used.

Thank you. The apology was necessary, perhaps more for my peace of mind than for yours.

That's not entirely true, but it's usually easier to just go for mechanics than to somehow design a bullet to be, say, immediately and excruciatingly painful (beyond normal pain from the wound).

~J

That makes no sense, Kage. You can't reliably quantify pain, either.