Why Penetration is too Important to Ignore

Penetration at oblique angles

Oblique angles

Unless you are  new to the topic of the defensive use of ammunition, you are probably well aware of the necessity of adequate penetration for defensive purposes. So if you already know why it is important, I’m going to beg your pardon for covering a topic that is so well known by folks in the know. But given how frequently this comes up in discussion on the forums and in the comments on TFB articles, there are clearly plenty of people out there who don’t know yet. If you are new to guns, if you are unsure of the importance of penetration, or if you just want to see my eloquent take on it, read on. If you already know, or if you’re a birdshot kinda guy with sticky elbows, you may want to keep scrolling.

When confronted with the 12″ – 18″ ballistic gelatin penetration standard recommended by the FBI, folks who are new to the topic of defense ammo understandably point out that people aren’t anywhere near 12″ thick. The heart is less than four inches deep, even in a disgusting fatbody like me, so shouldn’t 6″ of penetration be more than enough? If your assailant was made entirely of muscle tissue and stood perfectly motionless, with his arms at his sides, that might be right. But if he is a human being with a bone cage surrounding his vitals and held a weapon out toward you in his arms and if he moved as though he didn’t actively desire being shot, the projectiles you fire will have a very good chance of passing diagonally through an arm before striking the torso at an oblique angle. They may also have to pass through intermediate barriers before hitting the torso. After hitting the torso, a projectile has a pretty decent chance of hitting a rib. Bone in the arms and rib cage produces unpredictable results but it typically reduces total penetration and often causes deflection and fragmentation. So the problem isn’t penetrating a few short inches of soft tissue, the problem is that a bullet might have to pass through six inches or more of soft tissue and possibly bone before it even reaches the torso. And then it has to contend with more bone, and it may also hit the torso at an angle that requires even deeper penetration to reach the heart and pulmonary blood vessels.

This isn’t just hypothetical speculation on my part, either. The reason the FBI arrives at the penetration figures they recommend is by studying actual shootings. They found that both good guys and bad guys were often hit in the arms with bullets and that hits to the torso were often at an oblique angle as both parties maneuvered.

It’s also not uncommon for folks who are new to the topic to make the point that police shootings involve different circumstances than those that private citizens face. While it may be true that police have a higher likelihood of having to shoot someone in or around a motor vehicle, they do only have to shoot regular human beings like anyone else. The physiological necessity of causing significant damage to vital organs to bring about physical incapacitation is no different. And just because it’s a little less likely that you have to shoot someone around a car, doesn’t mean that you won’t. More importantly, the FBI recommendations involve ammunition that is tested in bare gel as well as against a variety of barriers. So, while the recommendation is indeed made for police officers, it was made while considering circumstances that you could face yourself.

While expansion, fragmentation, temporary cavity, and other factors do matter, no other factor is as important as penetration. If the bullet does not travel deeply enough in the body to reach vital organs, it cannot bring about physiological incapacitation in a timely manner. If you would like to know more about the reasoning behind  the FBI’s standard, please refer to these articles:





Andrew is a combat veteran of OEF and has performed hundreds of ballistic tests for his YouTube channel, The Chopping Block (https://www.youtube.com/user/chopinbloc). He is an avid firearm collector and competitor and lives with his family in Arizona. If you have any questions, you may email him at choppingblocktests@gmail.com


  • Sianmink

    Remember that gel and flesh are not equivalent objects.
    Ballistic gel provides a nice, consistent medium for comparing ammunition types against each other and gives a baseline for performance.
    It does not replicate real world performance.

    • No one

      Well of course Ballistic gel isn’t 100% accurate, unless you do the real deal FBI/Military test of getting the paperwork to put a nice pig or sheep to sleep, followed by putting it to sleep for good with a few gunshots, you won’t get the most accurate results possible barring shooting a live person.

      That doesn’t mean Gel doesn’t tell you some things, like when a round is going too shallow, is jammed too easily and won’t expand or just has poor expension through various barriers (including ones that nearly any attacker will have like simple clothing.)

      • Major Tom

        Paperwork? To hell with that! Go hog hunting in Texas or other places where you have no limit or license needed. If your self defense load quickly takes down a hog it’ll take down a human intruder.

        • No one

          You can’t really measure the performance of a round that way though.

          Let’s say you take a policeman who shoots and kills an armed, violent suspect and looks at the results, and then take a Coroner who’s trained for years to notice every single little detail on how exactly he died and what is and isn’t important.

          Sure, the policeman is obviously going to know the round worked, but the medical examiner is going to be the one who tells you how well and why when others can’t, and how much it came down to other factors like shot placement or entry angles, everything about the final moments an untrained person simply isn’t going to see.

          Also, someone who’s good and trained enough to know the physiology of a man, and their close matches like pig and sheep like the back of their hand aren’t exactly cheap or easy to find to do these types of post mortem tests.

          Basically, it’s not *just* things about ethics you have to sign off on, it’s also to show that the test has credibility and was/will be performed a certain way.

    • Chop Block

      Actual living bodies are not “equivalent objects, either”. Read the article I just published on how to properly interpret gel results.

      • Sianmink

        Just so.

        Living bodies are too variable and inconsistent, never mind the logistical and moral difficulties of using them in production testing. We need gel tests to establish and maintain ammunition performance standards.

        We seem however to have too many who think that 18″ in gel = 18″ in human, where it simply isn’t so.

        • Chop Block

          Well, it’s close, but yeah, not exactly.

  • BillC

    But, but, birdshot.

    • Major Tom

      Is for birds

  • No one

    “Bu….bu…but MUH LIBURTEE AMMUNITION! Muh round of tommorrow!”


  • ActionPhysicalMan

    Now this is information that a lot of people need to be exposed to. Good work.

  • marinepride

    My wife ignores penetration daily

    • AZgunner

      You’re probably using too small of a caliber.

      • marinepride

        This could be an issue

    • GaryOlson

      Disable or remove the armor first.

      • Twilight sparkle

        Why it’s always good to have extra protection?

  • AC97

    “But, but, muh Liberty Ammunition…”

    And remember, birdshot is for birds.

    • Chop Block

      You win the comments, AC97.

    • Go home, turn out the lights, everyone. AC97 just closed out the comments section like a boss.

  • Lt. Dan

    Am I too late for the “That’s what she said” joke?

    • BillyOblivion

      About 4 years, yes.

  • Risky

    Good information and great diagrams. Figure 11 is VERY common kind of trajectory to expect in a fight. When someone is scared or threatened, they usually take that ‘fighting’ stance where they squat a little, spread their legs and lean forward… kinda like a football lineman. A bullet fired from a regular horizontal trajectory is going to enter high and exit low. Another reason why that ‘high, center chest’ shot placement is also so important.

  • car54

    My son works in a trauma surgery unit in a large city and sees lots of GSWs. His advice is if you absolutely have to shoot someone use a rifle or shotgun (slug/buck), they make grisly wounds which are difficult to repair and are most often fatal. If you know you are going to be shot, hope it is with something smaller than a 9mm/38spl. Most GSWs with lesser rounds (and even some 9mm/38s) are usually result in walk in, walk out treatment. He also says, heavier bullets tend to penetrate more than lighter/faster bullets. Oh yeah, and shot placement is king, though he says it is almost unbelievable the path the bullet can take when the person who is hit is moving or jerks/reacts when hit.

  • Lew Siffer

    So if penetration is most important, is plain old cheap FMJ/ball ammo good enough for self defense?

    • No one

      In the sense that it will still kill someone (like it has for militaries for over a century ever since the Hague convention prohibited JHPs and SPs) when fired at them in the right places, yeah it will work, but It’s still better to just get a JHP that gets good penetration against flesh that doesn’t get hindered by clothing as you want as wide of a permanent cavity as possible.

      Pistols are pretty bad defense weapons as it is, don’t gimp yourself further. Militaries all over the world only do because they have to. (and pistols really don’t mean much on a modern battlefield anymore anyway.)

      • FT_Ward

        You only want as wide a hole as possible after the bullet has penetrated to vital organs. If bullet expansion prevents that width of hole is largely irrelevant in the short term.

    • Chop Block

      “Good enough”? Sure. But quality JHP that expands reliably and penetrates adequately is better.

      • FT_Ward

        It would be if it penetrated into vital organs but since JHPs are designed to have limited penetration you’re intentionally limiting your ability to incapacitate a felon.

    • FT_Ward

      Yes and it’s probably actually better. Expanding pistol bullets main purpose is to increase profit on ammo sales.

      • Young Freud

        Especially up north, where colder winters means thick clothing, which often means unreliable expansion with JHP. Either you get decreased expansion or it expands too quickly and inadequately penetrates.

  • Goosey

    One note: The original 1987 FBI Wound Ballistics Workshop did say “10-12 inches of soft body tissue at a minimum”, and that was later changed to 12 inches—according to Dr. Gary Roberts, “the FBI supervisor wanted a single hard and fast number as a bottom line minimum, so the more conservative 12″ was adopted”. I’ve seen some people who think certain loadings in rifle cartridges as large as .308 will “get you killed” because they only penetrated 11″ in calibrated gelatin, and therefore you’d be better off using a handgun to get that 12″… that’s pretty silly, IMO.

  • Chris

    These would all be rapidly fatal with exception of fig 8 on an obese or muscular individual with large pectorals and a very shallow shot trajectory. Adequate penetration is good, over penetration is bad, and shot placement is everything.

    • Dr. Longfellow Buchenrad

      Overpenetration is bad. Inadequate penetration is worse.

  • Jim

    Shot placement and penetration are the top killers. As a life-long hunter and 40 years as a cop, I have seen a lot of gunshot wounds. A bullet in the right place, no matter the size, will drop a person or animal like a rock. The bullet also has to penetrate enough to get to the vital organs to do it’s job. To me, bullet expansion is overrated, especially in small caliber handgun ammo.

  • Kodi

    Although I have read articles about ammunition purchases by various agencies of the federal and state governments, they usually only mention figures for total expenditures or number of rounds purchased and rarely identify manufacturers let along brands and types of ammunition purchased.
    That said, I’d like to see a listing of specifically which ammunition by brand, type, grain weight and other specs if possible on which ammunition is purchased for issue to field agents and police officers.
    We’ve heard this pitch a million times, but what do the pros use?

    • No one

      The FBI uses Winchester PDX1 for whatever that’s worth.