How to Properly Interpret Ballistic Gel Test Results

Side view of a ballistic gel block

Side view of a ballistic gel block

There is a lot of misconception out there about ballistic gel, which leads to some pretty bad conclusions about defense ammo. One of the more popular mistakes is the claim that ballistic gel is not an exact simulation of tissue. Paradoxically, this one is a little sticky because taken at face value, that’s actually correct. It isn’t a perfect simulation, but for that matter, actual living bodies are not a perfect prediction of what will happen in a shooting because every body is different, the exact angle of impact will vary, the tangent of the bullet to a round bone is literally infinitely variable, and many more significant variables are simply impossible to control. But properly prepared and calibrated 10% ordnance gelatin does produce penetration, retained weight, and expansion/fragmentation results that correlate very strongly with wounds observed in actual bodies. It is near perfect for simulating those measurements in living muscle tissue and the results in other soft tissues do not tend to deviate significantly. It is also homogenous and easily reproducible so variables can be controlled and results compared.

As a measure of what a projectile can do in soft tissue, it’s quite close, but that’s not quite what it is intended for. We aren’t meant to overlay an image of a gel block on a human torso and conclude that the damage will be exactly as seen in the block. That bone that I mentioned a moment ago tends to significantly affect performance. Bone usually fragments and bullets that strike bone can also fragment. Fragments from both tend to be low mass and penetrate shallowly but substantially increase bleeding near the impact. Bone can also prevent expansion for a JHP and it can deflect bullets from their original path.

The purpose of using ballistic gel is to compare one load to another in relative terms. We can see that two bullets penetrate about the same but if one expands more, it can obviously damage a bit more tissue. Or we can conclude that a bullet that fails to meet the 12″ penetration standard is likely to be less effective than one that performs similarly but exceeds the 12″ mark.

Where we see a lot of confusion, though, is when informal testers misinterpret gel results by believing that disruption seen in the gel is representative of wounding. Natural, collagen based 10% ballistic gelatin is much less elastic than real tissue and will tear easily. The tears seen in the gel block are roughly indicative of the general size of the temporary stretch cavity and can give an indication as to how early a bullet began to expand, yaw, or fragment. But real tissue (with the exception of brain, liver, and spleen) tends to stretch much farther without tearing. There is some disagreement among the experts, but a 2,000 fps impact velocity is often held as the threshold where the temporary stretch cavity becomes large enough to contribute to wounding through tearing. ClearBallistics clear gel is much more elastic than real gelatin or muscle tissue, but it will tear easier than muscle. If that sounds contradictory, consider that you can pull clear gel farther apart without tearing it, but it takes less effort to cause a tear. Kind of like how plastic wrap is both more elastic and easier to tear than a beer can. If you were to take a pork roast and try to push your finger into it, you basically could not cause your finger to perforate the meat unless you were very strong. I know that I can’t. But I can poke my finger into natural ballistic gelatin relatively easily and I can poke it into clear gel with a bit more effort. I can take a hunk of clear gel and tear it apart with my hands, but I would have great difficulty in getting meat to do that, except where it might separate along the various muscle groups.

The reason this distinction is important is that, when amateur testers point to disruption in a block as proof that ammunition is effective, they are flatly incorrect. Disruption seen in gel is a result of cutting or tearing and it does not correlate well with cutting or tearing that happens to real tissue from the same ammunition. That disruption might look cool, but it is not representative of anything that occurs in tissue. So when you see those videos reviewing the next gimmicky death blaster screw driver ammo, understand that the only results that the gel can give you that are actually relevant are penetration, expansion/fragmentation, and retained weight. If they make the claim that the disruption in the gel equates to “wounding” “permanent cavity” or anything similar, you may safely conclude that they really don’t know what they’re talking about. Their measurements may be accurate, but their opinion about the effectiveness of the ammo might not be.


Andrew is a combat veteran of OEF and has performed hundreds of ballistic tests for his YouTube channel, The Chopping Block ( 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


  • CommonSense23

    I would really like to see live tissue becoming a industry standard, especially for rounds that depend on fragmentation instead of expansion.

    • Chop Block

      As I mentioned in the article, actual living animals introduce too many variables to get useful comparative data.

      • ActionPhysicalMan

        Hopefully they meant lab grown tissue.

        • Paul Rain

          Eh, you shoot 10 gel blocks, you shoot 50 rapists, potato, potatoe.

      • CommonSense23

        And this is one of my major issues with not just ballistics testing but in multiple other areas as well. I mean look at Sig saying the 320 met all industry standards. If the number one selling point of doing something as a standard is its easy to test, cheap, and produces repeatable results. There might be a issue.
        I’ve seen MK255 gel test, I have also seen it shot into dozens of pigs during live tissue training, which we then cut up. I have also seen it hit people. The gel testing did not match the field use. I’m not suggesting giving up gel testing, far from it. But there needs to be a point after the gel testing where live tissue needs to be brought in.

        • Chop Block

          And the appearance of the gel isn’t supposed to simulate an actual wound. The problem is not understanding how to interpret gel results, not the test media.

  • ActionPhysicalMan

    I do feel bad for the guys that we know were trying to do good work but didn’t know that the wound cavity in the gel was not representative of what the would cavity would be in living tissue. I think that was a honest mistake for some channels.

    • Chop Block

      Absolutely. Doesn’t make their conclusions any more valid. I wasn’t trying to impugn their character.

      • ActionPhysicalMan

        I know you weren’t. I also feel for them because I thought the same thing until a year or so ago, and am a bit embarrassed.

        • Chop Block

          Same here.

  • Matt B

    Fill in the blanks:

    ________ many people have been killed by FMG bullets.

    ________ many people have been killed by hollow points.

    Just something to think about. The importance of expansion is as much industry hype as it is science.

    • ActionPhysicalMan

      Did you mean FMJ? If so, first off you don’t have those numbers yourself. Second, you’d need a significantly more information than that to determine the effectiveness or lack there of of expanding bullets.

      • Matt B

        Yes, FMJ thanks for catching the obvious typo. No, nobody would have those exact numbers but it would be easy to estimate them at 100 to 1 in favor of non expanding bullets. There have been thousands of gun fights ended with with FMJ or even round lead balls so why focus so much on expansion when it is statistically irrelevant. Maybe go to the range and work on shot placement instead.

        • William Elliott

          for most people, expansion is more about making sure the bullet doesn’t overpenetrate. FMJ is known to do that, and in the civilian world, thats a bad thing, vs full armed conflict where you want all the penetration you can get, and don’t mind if the enemy soldier behind the guy you just shot, gets hit by the overpenetrating bullet.

      • Chop Block

        I would be shocked if more people weren’t killed by spears (they’ve been around a great deal longer) than by pistols, but that doesn’t make a spear better than a pistol.

        • ActionPhysicalMan

          I think John Keegan in “The history of warfare.” stated that spears were responsible for more deaths, by orders of magnitude, than any other weapon type and maybe it was even more that all others combined. That book was really dry and not a fun read so I am afraid that I am not going to go back and check though:-)

          • Chop Block

            Not remotely surprising.

          • Matt B

            Fun fact, unless a bullet severs the upper spine or enters the brain it will not cause immediate incapacitation. Bullet wounds cause death by blood loss which takes roughly a minute or so. Those of you who are hunters know you can shoot a deer broadside through both lungs and the heart with a 30-06 and soft point ammo and he will still run 100yds before bleeding to death. Many people seem to have this fantasy that if they shoot someone in the chest with “brand x hollowpoint” they will fall dead instantly like they saw in the movies. In reality they will have the ability to fight for another minute until their blood pressure drops low enough for them to lose consciousness. It wouldn’t make a significant difference if they were shot in the heart with a FMJ, hollow point, or even a spear.

            The reason I use hollow points in my carry guns is for reduced risk of overpenetration and possibly faster blood loss from a slightly larger wound. Arguing “brand x” vs “brand y” hollow points is as pointless as arguing 9mm vs .45.

          • ActionPhysicalMan

            And all other things being the same, a bigger hole necessarily means a larger chance of injuring the CNS or severing a major vessel.

          • Matt B

            Probably not, but if you want to shoot gel blocks all day and conclude something from your findings knock yourself out.

          • ActionPhysicalMan

            At least you are right about how I squander my time, though I am in fact conclusion-less except for that very American notion that bigger is usually better;-)

          • William Elliott

            there could be an argument that MORE holes means larger chance of getting a CNS hit…just a thought…

          • ActionPhysicalMan

            William Elliott – Obviously there is such an argument (9mm guys employ it all the time) and it is a mathematically provable one just like bigger holes increases the chance. A 16″ shell hitting close to center of mass is very likely to hit the CNS – probably a 100% if POI is within 4″ of COM. 100 9mm bullets with similar accuracy probably have a very close to 100% chance also.

          • Kevin H

            There is a difference between immediate incapacitation and someone stopping their evil ways. Rarely does a criminal continue a course of unsocial behavior if their victim is shooting at them. There are of course exceptions, such as somebody high on drugs, but even a flesh wound that is not life threatening will normally cause your typical coward criminal to retreat.

          • William Elliott

            Hollyweird is getting better about that, depending on who did the movie. Case in point, just saw Atomic Blond…most times in the movies, someone gets shot, boom, thats it. The only guys that went down instantly from one bullet wound were the ones hit in the head. Everyone else fought, ran, etc, trying to either kill someone or keep from being killed. As violent as it was, the nod to realism was refreshing.

          • markrb

            That was surprisingly a pretty good movie!!

          • Nonya Bidness

            You’re way off base. Obviously clueless. I’d say you have no hunting experience whatsoever.

    • Stuki Moi

      The only real purpose of expansion, is to limit penetration. So you can have a projectile shaped for decent BC in flight, but which will take on a shape that yields greater resistance, once in tissue.

      Reporting of the somewhat arbitrary final resting min+max/2 frontal diameter as something valuable in and of itself, is at best speculative. And increasingly, as bullet makers gain more experience gaming the tests, possibly even disingenuous. For one, highly expanding bullets rarely travel straight all the way up until coming to rest. In addition, they don’t take on final resting shape immediately upon touching flesh. And, as those who handgun hunt with hardcasts quickly realize, wound channel size and bleeding, is at least as dependent on the flat frontal meplat of the bullet, as it is on it’s maximum diameter further down the shank.

    • Nonya Bidness

      Wrong, wrong, wrong, wrong, wrong. The number of people killed is irrelevant. Did you go to a liberal arts university for your statistics course? FMJ is nearly useless on live flesh. All it does is poke a hole and cause very little tissue disruption. The military uses because it has to. I know we didn’t sign the Hague Convention but we still adhere to it in that regard.

      Small bore rifle and handgun (.357 and below) cartridges absolutely rely on good expansion to be effective. Take away that expansion and you lose all your effectiveness. Big bores don’t need expansion to be effective and bullets of proper design can be very effective without it. In this case, a flat nose takes the place of expansion and produces a wound channel all out of proportion to what might be expected.

      But hell no, your assertion that expansion is industry hype is complete nonsense. If it was hype, we’d all be hunting with hardball. We are not.

    • Zebra Dun

      One thing shown is a JHP going through denim clogs up and doesn’t expand that is illuminating in itself.
      There is a youtube video on a forensics doctors view of bullet wounds.
      Dr.Andreas Garbinsky on gunshot wounds.

  • Scott Tx

    it does allow us to have a standard way of comparing bullet A to bullet B that’s reproducible by different shooters. In theory anyways.

    • Zebra Dun

      Beats getting Billy Bob to run down the range while we shoot at him!

  • Paelorian

    As damage to the gel block is not indicative of wounding, is there any way to measure damage caused by anything other than expanding ammunition at low velocity? I’ve long wondered about the validity of comparing gel block results of low velocity conventional expanding hollow point handgun ammunition, where all damage is due to the expansion and penetration of the bullet, which is apples to apples, to other types of ammunition, which seems apples to oranges. Rifle ammunition in general, shotgun slugs, high-velocity handgun ammunition and ammunition like the Lehigh Defense Xtreme Defender. None of those primarily cause wounding by simple displacement by the size and penetration depth of the projectile. When it comes to fragmentation or tissue tearing as wounding mechanisms (which occurs even under 2000fps, as proven by the Lehigh’s Xtreme series and slugs like the Brenneke Black Magic), existing gel mediums may be known to be inaccurate, but does any alternative exist other than typically anecdotal comparative results from hunting experience or testing on live anesthetized animals? For this reason I was skeptical of the Lehigh Xtreme ammunition when first introduced despite greater disruption in gel blocks compared to conventional hollow-points, but anecdotal hunting evidence gathered so far by users indicates that it does actually have excellent terminal performance in live flesh.

    • Chop Block

      The short answer is that the crush cavity produced by low velocity projectiles is limited almost entirely to the size of the frontal area. That is, at low velocity (pistols) tissue is only crushed by direct contact with the bullet.

      • matthew newton

        I can’t speak to pistol rounds, but my anecdotal evidence on hunting is that rounds below 2000fps can produce damage extending well beyond the size of the frontal area. An extreme example, but I hit a button buck at 20yds with a Federal Tru ball 2 3/4″ 12ga slug. The entry wound was about 2 1/2″ in diameter and roughly 3-4″ deep crater where it quickly skinnied up and the remainder of the path and exit wound was only a little over 1.25″

        A pretty extreme example as you have huge temporary displacement from a ~.72″ projectile striking that is also going to almost immediately flatten to well over an inch in diameter and you also have ribs and leg bones (struck just below the shoulder and at the front of the lungs) that are turned in to fragments.

    • Chop Block

      And there isn’t any “proof” from the Extreme Pretender line. The available science indicates that there is nothing special and damage should be consistent with any other solid of similar weight and velocity, especially if it has sharp edges at the nose.

  • Henry Reed

    Good writeup. Still working on that 45 gr Controlled Chaos load?

    • Chop Block

      I’ll get there. Lots of stuff to test. Keep an eye on the Arfcom YouTube channel.

  • Andrew wrote this article before I could. Damn you, Andrew. Damn you to Hell.

    (JK, great work!)

  • FT_Ward

    Exactly so the order of importance in a pistol cartridge- not the gun; concealability and usability are separate issues- is depth of penetration followed at a considerable distance by diameter of the hole it makes- after going through intermediate materials. Expanding pistol bullets (in calibers that would be commonly issued to police and the military) serve no purpose other than to be sold.

    Bullets going through felon’s torsos that then seriously harm innocents are so rare that they aren’t worth bothering about. I suppose one possible “test” could be to shoot 18″ thick gel (the supposed maximum) with two layers of clothing front and back, two sheets of drywall spaced as per a hotel wall with insulation then the gel blocks repeated. If spaces (i.e. several yards) were inserted between the blocks and dry wall hitting the second gel block would be the problem. Whatever the results were would not be fully “realistic” as the things that clutter up the materials between the muzzle and “innocent” gel- wiring, wall hangings felon’s bones, buttons, drywall screws etc would be very difficult to replicate with any consistency.

  • Mrl

    Maybe now they will just stop saying it or say this expansion in the gel is meaningless compared to the human body!

  • Anonymous

    I hate to sound like a fear mongerer or spread FUD but I think it’s safe to say if you were to ever shoot someone in a defensive situation and the prosecutor were to find out you spent your free time shooting simulated flesh with expanding bullets to study the wounding characteristics, it would be pretty easy for him to convince a jury you were a man obsessed with the idea of causing someone great bodily harm, waiting for the opportunity to inflict a horrific wound on someone.

    I’m just saying…

  • Nonya Bidness

    Great article and 100% spot on. I see it all the time and it’s nearly pointless to point out how people misinterpret gel results.

    I see some folks here even taking the article the wrong way. The article is not saying that bullet expansion in gel is meaningless but gel disruption is meaningless.

    • survivor50

      Agreed. It’s one way to see how projectile “A” compares to projectile “B” in a controlled media…that’s it.
      Your mileage may vary…

      • Nonya Bidness


  • Zebra Dun

    As for strikes on bone, once during a horse wreck I bailed off of a spooked bucking mare, I hit the ground good on my heels and did a forward roll coming upright in a sitting position.
    The Mare bless her heart ran over me her left front hoof struck my ribs a glancing blow as she went by and disappeared into the sunset.
    Three fracture ribs, I was down for a while and then barely able to follow and recover that mare, unable to ride I walked her the mile back.
    Then off to the emergency room.
    If a bullet of any style, shape and caliber hits bone it usually penetrates, that hoof hit bone and didn’t penetrate but it put me out of action for a couple of months and for about 30 minutes all I could do was lie on the ground and whimper.
    As for ballistics gel, I’d love to see the effect a 1000 lb horse doing about 20 mph hoof has on that.

  • Jeremy Nettles

    Thank you! I see this misunderstood by a lot of people who should really know better, on a pretty regular basis. Nice to see that SOMEbody gets it, and have a link to share now, rather than trying to explain it all myself every time.

  • The Heretic

    Excellent. I only ever look at the tests to see how soon a bullet expands, how much it expands, and how far it penetrates. I am mostly interested in whether the bullet expands at all – so much crap ammo with ‘soft points’ or HP projectiles that does not expand at all – it might as well be FMJ – maybe even worse because it doesn’t fragment or tumble in the medium like some FMJ does.

  • DChrls

    Great article. I honestly didn’t know the wound cavity in BG wasn’t representative to the real world. Glad I know differently now. I can say it’s never been a deciding factor, for me, in picking one bullet over another. Still, I’m glad I know better now.