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Simple Technical Question: Ballistic Gel Penetration

Discussion in 'Handguns: General Discussion' started by 94045, Feb 8, 2020.

  1. 94045

    94045 Member

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    I have a simple technical question. I really don't want this to devolve into a pro-gel or anti-gel.match. Please limit discussion to the question posed. PLEASE!

    In another discussion someone brought up the fact that elasticity of skin is not really a barrier to penetration when it is backed by tissue.

    I also have read of the study that correlates penetration in human soft tissue including skin to gel (+/- 20%).

    My question is:
    Why does the calibration bb penetrate 3.5" into gel at a velocity that has been known to bounce off skin covered human flesh?
     
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  2. JohnKSa

    JohnKSa Moderator Staff Member

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    If you poke around, there do appear to be some very official sounding sources that indicate the absence of a skin simulant in gel testing does affect the results.

    https://www.customcollagen.com/ballistic-gel-test-results/
    Ballistic gel is a fairly accurate representation of human and animal muscle and organ density, but it doesn’t represent skin or bones. Therefore, the gelatin tears more easily than skin, causing a margin of error that you will always need to account for.

    https://www.researchgate.net/publication/7900208_Ballistic_skin_simulant
    Hydrogels prepared from water solutions containing 10-20 mass% gelatine are generally accepted muscle tissue simulants in terminal ballistic research. They, however, do not have a surface layer which simulates the effect of human skin. The purpose of this research was to find a suitable skin simulant for enhancing the testing fidelity and the credibility of the results with gelatine-based materials when assessing the injury potential of not only high energy bullets, but also especially that of non-penetrating "less lethal" kinetic impact ammunition and relatively low energy ricochet fragments. A skin simulant also permits the simulation and assessment of exit wounds.

    https://techlinkcenter.org/technologies/ballistic-gelatin-dummy-with-resistant-skin/
    However, this type of simulant does not replicate the significant resistance that human skin provides in preventing penetration into sub-dermal tissue.
     
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  3. 94045

    94045 Member

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    That was kind of what I was suspecting but I didn't want to jump to conclusions. Hopefully if another explanation exist someone will post it.
     
  4. jmr40

    jmr40 Member

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    Ballistic gel isn't intended to accurately predict how far bullets will actually penetrate in living humans or animals. There are too many variables. There is no guarantee that a bullet which penetrates 18" in gel will penetrate 18" in a human. But a bullet that penetrates 18" in gel will penetrate deeper in a human than a bullet that only penetrated 12" in gel.
     
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  5. 94045

    94045 Member

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    I'm trying to figure out why the bb penetrates 3.5" in gel vs 0 in a human.

    It could easily have implications for comparison of bullets of different mass, frontal area and/or velocity.
     
  6. CapnMac

    CapnMac Member

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    Largely because it can. Which means it can be used as an index.

    Remember the gel is not meant to be a simulant (see much better description by @jmr40, above), it's meant to be a repeatable, consistent medium.

    back in the 70s, people used all sorts of things.
    Like "pine boards" that were "one inch thick"--well over a dozen non-specified variables right there.
    "Wet phone books" was another--phone books were listings of name and numbers of persons with landlines, and they varied in thickness from 30-50 pages in small towns to 3" & 4" tomes in bigger cities. So, you never knew what the medium actually was.
    "Wet Newspaper" was another.
    "Plumber's Putty" was another gun-mag-author favorite; but whether Duckseal, White's, RectorSeal or the like, maybe not gone into. Neither was how wet or dry it was mixed, nor how long it was allowed to set, either.

    So, it was all hoodoo (much like stacking 1 gallon water bottles and shooting those--all made by same maker, all have identical water fills by identical water--who knows).

    "Ballistic gel" (natural or clear) is easier to have uniform for testing. Pounds of dry into volume of water at what resting temperature. Does that replicate living tissue? No. Living tissue only vaguely resembles itself on average at best.

    Manikin does not resemble a person--except to show how clothes fit. Body punching bag does not much replicatea person, either--but, it's a good stand in.
     
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  7. Obturation
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    Obturation Contributing Member

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    @jmr40 & @CapnMac called it. Gel is just a consistent medium. You can poke your finger right into a gel block, unlikely you're doing that to a critter of any kind (unless it's a jellyfish)
     
  8. 481

    481 Member

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    With increasing regularity, it appears that many folks believe that 10% ordnance gelatin fails to correctly represent maximum terminal penetration depth of test projectiles in human bodies. Regrettably, the mistaken perception seems to be making the rounds on the 'net more and more....

    Between living human torso/soft tissues and properly prepared 10% ordnance gelatin there is actually a rough 1:1 ratio of both projectile expansion ratio and maximum terminal penetration depth.

    According to the research paper found here: http://ar15.com/ammo/project/fackler_articles/winchester_9mm.pdf

    Winchester 9mm 147-grain JHP bullets fired into—and recovered from—validated 10% ordnance gelatin exhibited an average expansion ratio of 1.20 and penetrated to an average depth of 13 inches. Matching the 10% gelatin test results quite closely, Winchester 9mm 147-grain JHPs recovered from living (at the time of shooting) human bodies (at autopsy) exhibited an average expansion ratio of 1.15 and penetrated to an average depth of 13 inches. (see excerpt below)

    upload_2020-2-10_13-17-18.jpeg
     
    Last edited: Feb 10, 2020
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  9. 94045

    94045 Member

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    So your position is that 0 vs 3.5" is not a descrepency? Or that slower lighter projectiles may show a disproportionate penetration in gel (my concern)? Or that since 0 vs 3.5" does not support your position it is to be rejected?

    If the study you quote is the one I believe it is it actually a study on what a minority of bullets do. All bullets that hit bone or exited were eliminated from consideration (Whether they only penetrated 6" or 18" before exiting).

    At best that study (which is biased by lack of consideration of bullets that exceed 13" and exit) is a study of gel vs living human soft tissue not the human body as you stated.

    I'm an Agnostic when it comes to gel. I'm waiting for a study that says it actually equates to the human body not that it equates under unique circumstances. That may very well be true but so far I have not seen such a study.
     
  10. bdickens

    bdickens Member

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    Nobody - at least nobody involved in the actual science of ballistic gelatin testing - believes that the stuff "equates to the human body."
     
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  11. WheelGunMan

    WheelGunMan Member

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    To expand on what Obturation said "Gel is a CONSISTENT medium" to compare penetration and displacement of various projectiles.
     
  12. ATLDave

    ATLDave Member

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    Ballistic gellatin is not designed to be a direct simulation of human tissue. It's designed to test the terminal performance of projectiles in a way that can be repeated, and in a way that can be used to make some predictions about real-world uses.

    Ballistics gel is analogous to the SAT. The SAT is not a simulation of college. It is, however, somewhat predictive of how students will perform in college (and more predictive than high school grades, even though high school "looks" more like a college simulation than a half-day standardized test).

    It is not a direct representation of college, nor is it a perfect predictor. But it can be administered in a controlled way, and the same student taking it repeatedly will generally score in a relatively consistent range. It is pretty darn "reliable" (technical term for testing repeatability) and is currently considered sufficiently "valid" (technical term for how predictive of real performance/real attribute a test is) to be useful.

    Similarly, ballistics gel testing (when done correctly) is highly reliable and has a useful level of validity. Just as with the SAT, a highly-reliable, adequately-valid test is extremely attractive to institutional decision-makers.
     
    Last edited: Feb 10, 2020
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  13. 94045

    94045 Member

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    Okay let's get back on topic.

    For the sake of this discussion anyone that has doubts about gel suspend them.

    I simply want to know why the bb will bounce off humans at the same velocity it will penetrate 3.5" into properly prepared gel.

    One person has said, "Because it can". I believe that may be the only person besides JohnKSa - Moderator Extraordinary that has directly tried to respond to the actual question.
     
  14. ATLDave

    ATLDave Member

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    Why can a person make a 450 on the SAT in 4 hours, but it takes a minimum of a full semester, or sometimes two, to flunk out of college?
     
  15. 481

    481 Member

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    Classic straw man argument. I never made any of those statements or claims so I see no need to respond to them.

    When comparing paired data (the maximum terminal penetration depths of bullets in both mediums), it is not reasonable to compare complete and incomplete wound channels to one another. This is evident to even the most novice statisticians. Excluding useless/unusable data is necessary to make valid comparisons.

    Actually, it is if you read the paper. Measurements of bullet expansion ratios and terminal penetration maxima were taken from testing conducted in 10% ordnance gelatin and human torsos—which are typically regarded as being the combined thoracic and abdominal cavities—at autopsy.

    You are certainly free to discard existing data/research as you wish, but that does not render it invalid.

    Waiting isn't likely to be very productive either.
     
    Last edited: Feb 10, 2020
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  16. 481

    481 Member

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    Some folks are 'book smart' and test well, but struggle in the real world. Such tests can provide clues as to how well some can do, but unless they actually apply themselves to the task and do so efficiently and effectively, there is no guarantee of success.
     
  17. 94045

    94045 Member

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    Let's stick to simply soft tissue penetration for a second.

    These are simply example numbers to illustrate my point so don't make to much of it.
    60% of the bullets penetrate soft tissue only.
    20% of those penetrate less than 13" and exit.
    20% of those penetrate more than 13" and exit.
    Of the 36% remaining in the body that don't hit bone they average 13" of penetration.

    My contention is that bullets that penetrate more than 13" are more likely to exit the body and by making no allowance for this you have an artificially low soft tissue penetration number. If you allow for that now you have to consider that a similar percentage of the bullets that happened to exit sooner would also have been likely to penetrate deeper farther skewing your results.

    So my point is saying 36% of bullets behave in a certain way is a long way from conclusive.

    Just looking at the numbers my suspicion is that in reality average soft tissue penetration would be higher and overall penetration lower if the target had been such that we had no exiting rounds and considered 100% of the projectiles.

    I am not arguing that ballistic gel is a bad design and test medium but I do think the people that argue that it is not representative of the body as a whole and you can't expect that kind of penetration in a body do have a point. If I have to shoot through the skin and sternum it's not unreasonable to expect the penetration may be reduced over a gel test.

    Especially since nobody has yet explained the 0 to 3.5" descrepency. That bb is a projectile, like it or not.

    My inclination is to believe less dense organs tend to offset the loss of velocity of the skin and be the reason that we don't have to account for it but so far nobody has mentioned that explanation so it may be an out of left field shot.
     
  18. WrongHanded
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    WrongHanded Contributing Member

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    I'll take a stab at this, although honestly I think the question has been answered sufficiently already.

    The gel is not intended to replicate the human body. It is intended to compare and contrast various types of ammunition, against one another. Not against the human body. Why this is, would be a separate question. But to try and replicate a human torso would make the comparison of projectiles very complicated.

    The BB is used to confirm that each piece of test media (gel) has a high level of consistency with all other test media. This is because if one piece of gel is softer or harder than the next, the results found from ballistic testing on each piece would not be comparable. You can't measure differences between two separate events, without a constant metric. Which is why we measure penetration in inches and not, for example, potatoes.

    images.jpeg

    So, it really doesn't matter what the BB does to a human body. It only matters that it can be used to test each batch of gel to confirm it is made to the required specification.
     
  19. Hartkopf

    Hartkopf Member

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    The BB test can be a repeatable way to calibrate the gel but it is done at such a low mass and velocity that it doesn’t actually correlate to anything the gel block will be used for.

    One comparison that comes to mind is running a compression test on an engine. The engine is spun over several times just using the starter motor at aprox 250 rpm while a gauge is used to measure cylinder pressure. Readings can give several clues as to how the engine will actually perform while running at 7000+ rpm. This is a common and useful test but it will not forecast horsepower or give much indication as to how well the engine will start before the race.
     
    Last edited: Feb 10, 2020
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  20. ATLDave

    ATLDave Member

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    True. Of course, the SAT isn’t designed to predict success in life, just ability to succeed in undergrad schooling. It’s not a perfect predictor of even that, though. It’s just a better predictor than anything else that is easy to measure.

    I’d say that goes for gel testing, too. It’s not a perfect predictor. Not at all. But it’s the most reliable readily available test, and it has SOME validity. So it gets used a lot. Again, just like the SAT.
     
  21. 94045

    94045 Member

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    This I can agree with. The problem I have is with the explanation that it's a 1:1 predictor in the human body. At best it's a predictor for if you manage to miss all bones (and I've already stated why I think even the studies of that had some issues).

    I agree it's the best we have. I also believe unless you miss all bone you may get shallower penetration in the human body. Apparently I'm not alone because my understanding is proposals to increase the minimum penetration standard have been made several times.

    I'm still somewhat concerned that if a low velocity light projectile will penetrate gel (bb) it may be indicative that something like a 700 fps 29 gr .22 may have an artificially high penetration in gel and a 2000 fps 400 gr .500 may have an artificially low penetration.
     
  22. 481

    481 Member

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    Of course bullets that penetrate more than 13 inches are more likely to exit the body.

    However, as noted above, it is not possible to accurately compare a partial wound channel with a complete wound channel for statistical evaluation since there is no way of knowing how much father the bullet making the partial wound channel would've gone so that both total wound channel lengths can be compared against one another. In the 28 cases (cited in the research paper) of the Winchester 9mm 147-grain JHP striking and passing through living human torsos and all of the different types of visceral and muscle tissue that we'd expect to find in them (lungs, heart, liver, stomach, pancreas, spleen, kidneys, intestines; large and small, vascular tissues, adipose tissue, muscle, etc.) we can see for ourselves that the test results (nearly identical expansion ratios, same average penetration depth of 13 inches) support the ability of correctly prepared 10% ordnance gelatin to represent reasonably the roughly 1:1 ratio of terminal expansion and penetration depth of bullets in the human body—esp. the torsos used in the comparison.

    Sticking to soft tissue then as you ask—just as was done in the quoted study http://ar15.com/ammo/project/fackler_articles/winchester_9mm.pdf —we have the ability to compare directly the terminal performance of an identical JHP design (the Winchester 9mm 147-grain JHP) as it behaves in both mediums—human torsos and 10% ordnance gelatin. I would have preferred to have access to a much larger sample population than the n = 28 presented in the paper, but until someone else repeats the procedure in the research paper, we have only that which we have.

    While it is always an option to discard the study, there appears to be no other study available that provides a comparison of a specific JHP design directly across both mediums. Such an approach serves only to return us to the device of speculation to debate the matter.
     
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  23. 94045

    94045 Member

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    We have the ability to compare the bullets that remained within the body and penetrated soft tissue only against gel.

    I also understand that as you state that the sample size is a bit small.

    I don't have an issue with gel as a muscle tissue simulate. I believe it does it very well. I have a problem with people trying to claim its a direct 1:1 comparison to a shot that penetrates skin, structural muscle, structural bone, lung tissue, heart and cervical bone.

    I don't have a problem with saying the bullet that penetrates the deepest in gel (within a caliber and weight) will likely penetrate the deepest in a human torso (regardless of what it hits).

    I am concerned that the bb calibration test is telling us something about a possible inconsistency where a low mass, low frontal area, low velocity projectile may show an artificially high penetration in gel and the opposite may be true. A high mass, high frontal area, high velocity projectile may have an artificially low penetration in gel.

    In other words it's possible a .35 - .45 projectile at 800-1400 fps may be very close but the farther you get from that range the less accurate it could be.

    I guess I'm asking if a study of this possibility has ever been done.
     
  24. Slamfire

    Slamfire Member

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    I have assumed that must be the case. What is the use of a test media that does not simulate human tissue in terms of bullet expansion, wound depth, and crush space? Might as well go back to wet phone books or dux seal if all that is wanted is relative results. And I remember a revolver article claiming bullet penetration in steel was a wound simulation!. I used to read all the time bullet expansion in clay or soap, because big deer are made of mud and fawns are made out of soap flakes.

    Dark Matter Unicorns are a different matter

    rJhFDjh.jpg
     
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  25. Kleanbore

    Kleanbore Moderator Staff Member

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    The calibration b is fired at 590 +/- 30 FPS. That's quite a bit higher than the velocity from a spring gun.

    From where comes the assertion that is would bounce off human flesh?
     
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