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So gigag04's post about the .40 caliber brought a question I have had back to my mind. I don't really understand a lot about ballistics and most articles I have tried to read about it assume an understanding I do not yet have. So I am hoping some of you can give me the layman's overview to the question below:

If one of the concerns about 9mm rounds is the potential for over-penetration, why is it desirable to increase the pressure by loading it +P? All other factors being equal (i.e. mass and shape of projectile, length of gun barrel, etc), wouldn't a round with increased pressure have a higher velocity and therefore be even more prone to over-penetration?

Thanks in advance,

t

edited typo ...

Gosh, I hadn't heard that over penetration was a concern for 9mm!

...with a hollow-point, the extra speed USUALLY causes the expansion to be increased earlier...helping the energy be left in the flesh, rather than an unexpanded bullet passing on through, with less effect on the person shot, and more danger from overpenetration...
...you can find good info on 9mm by searching the forum for Steven Camp's articles, or GOOGLE Steven Camp on 9mm ammo...

...not saying I agree with all of this article, but came across it just now and it may help you...

http://www.americanrifleman.org/article ... n=Triggers" onclick="window.open(this.href);return false;

terryg wrote: ...wouldn't a round with increased pressure have a higher velocity and therefore be even more prone to over-penetration? ...

Keeping all other variables (bullet weight, construction, bullet type (JHP/FMJ)) the same, I think you are probably right. But..

I have chronographed a number of 9mm and 9mm+P rounds, and found that +P designation by itself does not always -- usually, but not always -- indicate higher velocity. Seems odd, since my understanding is that the +P designation is supposed to follow SAAMI standards, but maybe there is a lot of variance in the standard -- or manufacturers' adherence to it. Even if you stay with a bullet of the same weight, (which I assume you probably assumed), strange things happen in real life.

Some examples from chrono'ing a Kahr P-9:

115 gr Corbon DPX +P............. 1076 fps
115 gr CCI Blazer FMJ..............1091
115 gr Speer Lawman TMJ........1127
115 gr Speer GDHP.................1174

Note that the +P round is the slowest in the group. DPX is the all copper round, maybe it is "grippier" against the rifling? And it has a great reputation for expanding in gelatin after penetrating all kinds of materials.

Now for Speer's 124 gr GDHP, +P does add a little more zip: 1090 for regular version, 1171 for the +P round.

Wow - that is indeed very complex. But I think I understand a little better now.

To boil it down:

-Essentially 9mm ball ammo, because of smallish diameter and very high speed, is huge on over penetration.
-JHP, on the other hand, because it expands should reduce the penetration to the effective range.
-But sometimes JHP doesn't expand like it should. When that happens, it is essentially acting like FMJ and therefore might over-penetrate.
-By increasing the speed, a JHP round should expand more reliably which should help prevent over-penetration.

Sounds about right? Thank you all for your responses.

1 not even 2 modern JHP like (9mm) Gold Dots hitting center mass would be devastating. It would at least send the guy to the critical care for a while. Recovery my be possible but with life long lasting disabilities and/or medical issues.

As a practical matter, +P commercial ammo is almost exclusively loaded with expanding bullets.
I don't recall ever seeing +P on a FMJ commercial round

AndyC wrote:FMJ in +P is normally found in ammo designed for SMGs - more because of the extra pressure needed to cycle the sometimes heavier bolt and stronger recoil-spring on SMG's than any improvement in terminal ballistics. IMI in Israel is one manufacturer of such ammo, which can be found on the market but... there's no real demand for that ammo for civilian pistols, no.

But that ammo isn't actually marked +P, is it?
Nor is it generally found in retail stores.

If anyone wants to try it, I have some Speer Gold Dot 115gr +P+ in 50 round boxes.