Is Over Penetration a Myth?

over penetration

Is the whole over penetration issue a non issue?

We have had quite a few posts on this page about ballistics and how rounds behave. One issue you always hear about is over penetration. What we are talking about is a round going through a threat and striking an innocent.

What we are not talking about is missing the threat and the round either hitting a friendly or going through a wall and hitting a friendly. That's called a miss.

The whole issue is that if you select a pistol round due to worry for over penetration you are compromising your weapon's effectiveness. You should instead be working on your marksmanship.

There's an excellent report done by a FBI agent that stresses that over penetration is greatly exaggerated and that the far greatest danger to friendlies is by stray round.  Download the report here.

We also found  good video that discusses over penetration. Take a look and let us know what you think.


  1. Yes over penetration is an issue…I have personal experience with this…7 rounds of 9mm standard NATO ball passed threw a target at 11 yards, 3 of those rounds continued and wounded 2 civilians. Thankfully it didn’t kill them, however any high velocity round can and will continue. I think you have down played this way too much. Low velocity, heavy hitters are the best option. As you said in your video, it’s a possibility, and as the shooter, it is my job to be sure of my target and beyond. Not to mention, what if it isn’t a human bystander I am worried about? What if there is sensitive objects on the other side….Ammo, Explosives, electrical, gas cylinders? This is all about being a more effective and safe shooter. I do agree it starts by hitting your target, I disagree that over penetration after a good hit isn’t an issue.
    Semper Fi

  2. Randy I believe the intent was to shooters within the US. FMJ tends to carry on through targets and is partly what pushed bullet development onward. That and better wound channels to stop / end the threat / target.

    Over penetration happens and that is why any instructor worth their salt strives to maintain focus on the training maxims of “ensuring your target AND backdrop”. That being said I offer this up from my experience:

    I tend to pull or push my shots if I’m focusing on perfection or involving too much noise in my head. It erodes my marksmanship. Focusing on hitting what needs hit is much more relevant or you have a clean miss going on into whatever is in the path of the bullet

  3. I just read the FBI Report, which goes through all the types of penetration, except for over penetration. It basically say that you need 12 to 18 inches of penetration with a bullet that will deform to cause the most damage. It also stated that under stress that only a few shots will hit center mass. So I don’t get your whole, “you need to work on your marksmanship” comment. I do believe that practice and marksmanship are important. But as the FBI report stated making a head shot or upper spin shot are a much harder shot to make. so we shouldn’t be aiming there. So you need ammo that will do the most damage to the torso. That is why we don’t carry FMJ practice ammo in our EDC self defense gun.

    I really don’t get the relationship of your article that you linked to the FBI report.

    • Start reading on page 11 at the Ammunition Selection Criteria chapter. You have to extrapolate a bit where it talks about the requirement for a bullet to penetrate at least 12 inches to be effective. Also he talks specifically about the over penetration issue here- “An issue that must be addressed is the fear of over penetration widely expressed on the part of law enforcement. The concern that a bullet would pass through the body of a subject and injure an innocent bystander is clearly exaggerated. Any review of law enforcement shootings will reveal that the great majority of shots fired by officers do not hit any subjects at all. It should be obvious that the relatively few shots that do hit a subject are not somehow more dangerous to bystanders than the shots that miss the subject entirely”

  4. Silversax42 says:

    I agree thaT it is pointless to choose a gun or caliber based on the fear of over penetration. I don’t agree with ignoring it in your ammo selection. Any DEFENSIVE round with a solid hit should lose enough steam passing through the target to be relatively safe no matter the caliber, but ball ammo will not.

  5. Ball ammo, or JHP, either way, a 9mm is prone to pass through and through. A .45 acp is the most effective handgun and ammo, and is far less likely to pass through.

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