Thursday, September 15, 2011

Stopping Power and the .25 ACP

I have been thinking about the Ellifritz stopping power study already mentioned and linked here.

I thought it might be interesting to consider each caliber or category individually and do some basic rambling.  First, though, we recall that Ellifritz differentiated between the “one-shot stop” percentage and the “actually incapacitated by one shot” to the head or torso.  Let’s figure out what that means.  Quoting Ellifritz:
One shot stop percentage - number of incapacitations divided by the number of hits the person took. Like Marshall's number, I only included hits to the torso or head in this number. 
Percentage of people who were immediately stopped with one hit to the head or torso.

In the second case we are talking about one shot fired, one attacker stopped.  While in the first case we are talking about aggregate numbers for those who were taken down and/or out. 

To make it easy to think about, let’s use round numbers.  Say you have 10 individuals who are shot with weapon X and all of whom are incapacitated.  Six of the baddies go down immediately after one hit to the torso/head.  Weapon X has a 60% “actually incapacitated by one shot”.  But say that of the other 4, one is hit twice, two more take three hits to go down, and one big baddie takes five hits.  The formula for the “one-stop shot %” would be:

10/((6*1)+(1*2)+(2*3)+(1*5), or, 10/25 = 0.4, or 40%. 

That is assuming, again, that all ten are eventually incapacitated.  But we see that, by category, anywhere from 40% (.32 caliber) to 9% (rifle) are never incapacitated at all.  The fight ends for whatever reason, and the attacker, though not down and out, ceases to be a threat -- or, perhaps, worst case, the defender loses the fight because the attacker was not incapacitated.   The non-incapacitation percentages are important to consider.  In the case of the .32, that caliber fails to incapacitate at all 40% of the time, but it had a very impressive 72% stopped by one stop to the head or torso, and a respectable 40% one-shot stop percentage.   The sample size is smaller for the .32 than for any studied caliber other than the .44 magnum, but one tends to think .32’s are the caliber of choice in domestic disputes and situations where the range is very short. 

This brings up an interesting point in that we do not know the circumstances for any given situation.  A gunfight between military personnel and enemy combatants has a completely different dynamic than a man who decides to slap his old lady around because the Bears lost to the Packers.  An unarmed attacker is, in many cases, going to be easier to dissuade than someone armed equivalently.  A home invasion shooting is different than an attack motivated by revenge or jealousy.  And, of course, the classic example is that the actions of meth head high on his drug of choice are going to be very different from those of a sober, somewhat rational person.  It is even true in the field when hunting.  An animal with no adrenaline pumping from flight or fear is much easier to take down than spooked game. 

With all of that in mind, let’s look at one of the lesser choices, the .25 ACP.  Here we have, unlike the .32, a fair sample size of 68 people, with 150 shots fired.  Of the people shot with the pathetically lame .25 caliber – and these are always chambered in very small autoloaders, 25% died as a result of their wounds.  The .25 killed seventeen people.  It did not kill fifty-one.  Still, seventeen corpses from a mouse gun should make people stop and realize that any firearm is capable of dealing death and is not to be handled careless or deployed lightly.  All shootings are serious business. 

For the .25 ACP, there was a one-shot stop rate of 30%.  When one looks at the rest of the chart, it is sobering to see that the measuring stick for handguns, the .357 magnum, has a one-shot stop percentage only fourteen points higher (still under one-half), and the .25 is only nine points lower than the mighty .45 ACP.  We will say it again:  handguns are not good stoppers.  When it comes to handguns, the rule is that if it is worth shooting once, it is worth shooting three times.  That may not always be possible but remember it.

It is not surprising to find that the tiny firearms chambered for the .25 ACP do not lend themselves to accuracy.  Also, I suspect that those who carry a .25 probably do not get a lot of range time with it.  Hence, we see that the head/torso hit percentage of the .25 is low – 62%.  Every other handgun is around 75%, that is, until we get to the rounds typically chambered in larger weapons – the .357, .45, and .44 magnum which are all above 80%.  It is easier to get on target and get off a good shot with a larger weapon.  Also, these are weapons employed more by experts, if not professionals.  I am surprised that the 9mm and the .40 S&W do not have 80%+.  The 9mm is chambered in smaller weapons, so that might be part of the issue.  Also, I wonder if military use of the Nine results in it being used at longer ranges?  I have no explanation for the .40, which is my carry weapon.  My XD will group around 2 inches at 25 yards, offhand, if I’m doing my part.

But back to the .25, the final statistic to look at for this round is the percent actually incapacitated by one shot which is only 49% -- amazingly the 9mm is lower at 47%.  This has got to be a function of military ball ammo in the 9mm. 

All things considered, I would be reluctant to carry a .25 ACP even as a backup.  It will work, most likely, at very close ranges especially if fired into an attacker’s head.  It is far better than nothing, and a hit with a .25 can easily prove fatal.  Cheap .25’s maybe the only weapons available to and affordable by some folks.  I would hardly be willing to deny a person the right to defend himself or herself because of dearth of funds.  If using a .25 out of necessity or because it is convenient to carry (and it is), one should look for good, expanding ammunition and test it for reliable functioning and accuracy if at all possible.  These little guns should be kept clean and be properly lubricated.  If a person needs one, it absolutely needs to go bang.  As we noted, this is not a toy and not something to left where children or other irresponsible people could access it.          


  1. Great article! I own a very small bauer 25. One would have to imagine that a firearm is not a death ray by any stretch of the imagination. I believe with proper shot placement it will kill.

  2. I agree. Shot placement is probably something like 90% of the deal, with good ammunition being the next most important factor.

    The thing about the smaller weapons is that you are that much more likely to have it with you in nearly every situation. And the #1 rule of a gunfight is, have a gun.