Ballistics:  The Ogre Defensive Power Factor


I was talking with one of my brothers about some different calibers and velocities. Something we often talk about.  This led to the IPSC's Power Factor, which is simply Bullet Weight in Grains, Times Velocity, Divided by 1,000. This is an easy formula that one can use when comparing loads... but doesn't take into effect Caliber. W x V / 1000= PF. Nice - but not enough. I personally think Caliber is a CRITICAL FACTOR in a defensive bullet. 

I have been thinking about this for a few minutes now, and I think I have another similar formula that will be more accurate when looking at and comparing different loads.

One of the most popular methods of comparison is the M&S OSS%.  I think the M&S study has some merit, but the study, due to its critical flaws, has been debunked as junk science. (more on that later) So a simple mathematical formula like what the IPSC uses should be of some help. IPSC's goal was to create a certain level that allows people to compete on a more even playing field.

This is a new scale... So the numbers are going to look different, but bare with me. Once you starting running this formula with different calibers and loads, you will see some interesting results:

Bullet Weight in Grains, Times Caliber, Times Velocity, Divided by 1000 = Defensive Power Factor or DPF for short.
For 9MM and such you of course use its actual measured Caliber .355 or what ever your bullet is actually sized at. 10MM is .40 cal etc.

A 230 grain .45 load: 230*.45= 103.5 *900/1000 = DPF 93.15

Smaller caliber bullets will have smaller numbers, and mouse guns will look more like mouse guns that they are on this scale. That's why we call them Mouse Guns.  Donít get pissed at me if your choice of a carry package looks wimpy.

No Ė the DPF its not perfect... but its simple. K.I.S.S!  That is the whole point.

Just for fun - lets look at the .454 Casull:
300 grain bullet, .45 caliber, 1650 FPS speed = DPF of 222.75! Too Bad that .454 Casull pistols make poor Carry Guns!

The DPF Formula works on rifles as well, but you need to change the scale.  For Rifles, donít divide by 1000Ö Divide it by 100.


Now, the Speed Freak guys that think faster is better might be getting a little irked here. But I think this is showing a more accurate picture. I mean, everyone knows .308 hits harder than .223, so these numbers should not surprise you. You have a bigger caliber, heavier bullet... it will hit harder that a smaller, lighter one. That's physics. Putting Egos aside - I think that this is a simple and easy way to compare loads.  I am not suggesting you compare Rifle calibers to Handgun Calibers in terms of effectiveness - but it is useful when comparing Rifles to Rifles... Such as .223 and .243... And .300 to .338 etc

Will this end the 9MM vs. .45 debate? No. (but it should, damn it!) The speed guys continue to talk about Hydro Static Shock.  I donít have a formula that factors in Hydro Static Shock... as we donít have a way to accurately measure that. The 9MM vs .45 debate is one of the eternal issues for the gun culture to talk about.  Personally, I favor making as big of a hole in my target as I can.

To full understand the DPF theory, one must understand the background to the ISPC Power Factor. The reason for the two different classes has to do with scoring. A 9mm typically has much less recoil then a .45. This way, the playing field is somewhat equal. However, a 9mm bullet can still make major (.38 Super). On the other hand, it'll have much harsher recoil then a minor 9mm. The reverse can be applied to the .40 S&W. It can be shot in the minor or major class depending on the PF. This is where reloading is a big bonus.

IPSC PF = wt * V / 1000

Where: wt=weight in grains, and V=velocity in fps

Major is from 175 up.
200 gr. .45 bullet at 900 feet/second = 180 power factor.

Minor is from 125 to 174.999.
125 gr. 9mm bullet at 1000 feet/second = 125 power factor.


Adding the caliber to the formula gives us a yard stick for itís defensive potential.  This formula favors bigger calibers, and heavier bullets... But then again - IPSC's formula was weight friendly too and people can moan about hydrostatic shock but that fact is bigger caliber bullets make bigger holes. If you have ever seen with your own eyes the dead bodies of people shot with handguns... you see just the hole and wound channel... You donít see any temporary wound cavity.  


.38 Casull, .38 Super, .357 SIG... I think the formula is fair to those as well because they are all actually firing similar sized bullets.  Letís be realÖ they are all ďFast NinesĒ launching the same pills.  The only differences that matter here are the weight of the slug being launched and the velocity itís launched at.  

Letís look at the smaller calibers for a sec. Run your favorite .32ACP load against other .32ACP loads. Now compare the .32ACP vs. .380ACP.  Toss in the new .32NAA cartridge.  What about .22 vs. .25?

I think once you starting lining everything up you will see that everything falls into place rather nicely and anything with a DPF over 40 is a potent load that you could carry for CCW with confidence.

Bullet types are interesting... Hollow points donít always expand. How could you factor that in the equation and keep it simple?  Probability of expanded caliber after the bullet stops, Starfire vs. Hydra shoks? Lets not go there.  But - if you want - it might be fair to give your self a .5 point bonus to your hollow points should they expand as advertised.  Thatís up to you.  Use the formula as you like.  

The first person that raises there hand to ask about SHOT SHELLS will be flogged by chanting nude Gregorian monks with whips!

Okay, what about shot shells?  What the hell.  Letís go ahead and look at that for a bit.

Since shot shell loads are so different, the only to give these a rating, is to combine the DPF scores of the individual shot within. This will give you the POTENTIAL DPF, since the shot will spread on the target and many of the pellets may miss.  You'll need a micrometer to measure some of these... Do the DPF on one... then multiply that against the number of pellets.  Same thing with loads that have different sized pellets.  Factor all the different sizes.  Potential is all you can have on the shotshells, but it still works.  Now some shotgun guys are going to complain about something here, but give it a rest.  Take comfort in the DPF score of one of your slugs!  Judas Priest!


You canít create a formula that will take EVERYTHING into account including expansion, fragmenting, and shot placement.  It gets too complicated.  Can't be done. Simply can not be done.  Because you would have to factor in bullet shape, jacket thickness, the targetís mass, air density and humidityÖ a million things.


Now, more on M&S ratings.  Marshall and Sanow's theory is erroneous. They gathered police shooting and autopsy reports. Then culled out all cases where an individual that was shot received only a single gunshot wound. That wound had to belong to the upper torso (what we commonly call Center of Mass.. COM). All other shootings were thrown away and were no longer part of the analysis.  Marshall and Sanow then took all of one hit reports and determined how many of them resulted in a "stop," which they define as a ďcessation of hostility within a certain time periodĒ. The figure represented a percentage of all the single COM hit cases, is the official "one shot stop percentage" for that caliber.  Their study is dramatically flawed due to the discarding all incidents where it took more then one shot to stop an individual. The reason for the flaw happens when you must use deadly force, you keep shooting until the person stops attacking you. Therefore, the odds are extremely high that if you only fire at someone once, it is because he stopped attacking you after one shot and fell over dead. In those cases where only one shot is fired and the attacker did not stop, that is likely due to the BG taking your gun, or killed you. 


Many of the forensic studies show that a single shot to the CNS (central nervous system) will result in an immediate stop. However, the difficulty of a CNS shot is very high. The majority of CNS shots are by good luck. Marshall and Sanow ignored several variables like the type of firearm used (barrel length, rifling type and rate of twist, etc), specific shot placement, angle of shot, etc. Yet, all COM results were discarded by M&S.

Itís humorous looking at their 93 to 96% "one shot stoppers." On the other hand, most people are aware that handguns simply arenít that powerful. One only needs to ask an EMT. If a 96% on shot stops meant that a round had a 96% chance of stopping an individual, then shooting someone twice with that round should yield a 99.8% chance of stopping the attacker. Thatís as close to 100% as you can get, and no one is suggesting that a double tap with any handgun ammo can guarantee a stop. What about the other 90+ percent of shooting incidents where there were multiple shots to the COM? Why didn't the attacker die after one shot if it's a 90+% one shot stopper?

Basically what Iím blabbing is, there are no fool proof formulas. Marshall and Sanow do have some good points. However, a majority of their study is flawed. If they had relied more heavily upon physics and ALL shooting reports, their study wouldíve been more realistic.

My advice is carry the biggest, most comfortable caliber that YOU WILL HAVE WITH YOU AT ALL TIMES. Itís pointless to say that the 44 mag is the best CCW if itís impractical for you to conceal. If you canít hide it well, then you canít carry it.  If you canít carry it, then what is the point?  Itís better to have any gun in a defensive situation then no gun at all.

So - where does this leave us?
With a simple formula easy enough to run in your head while shopping for ammo or looking at two pistols and your thinking which one is for you. It is a mental Ballistics Gel Test.

If your looking for a formula for determining the Magic Bullet - It isnít gunna happen, there is no Magic Bullet... Only in the movies. Even the Seeker Bullets from the Movie "Runaway" didn't work 100%. Maybe .50BMG could be it, but you can't that fit that into a 1911...

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