A gel expert explains
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I looked at the referenced paper and it's an example of how complex fairly rigorous solution would be to analyze high speed bullet penetration even in gelatin. They divide the analysis into 5 separate regions (elastic, plastic, hydrodynamic, sonic, and explosive) and there is no single equation that describes bullet behavior in all these regions -- and each region requires approximations of material behavior to be mathematically "tractable." As is the case with nearly all real, physical situations, it's all approximated to some extent depending on assumptions employed to make it mathematically "tractable." However, in case of handgun bullet velocities in gel it's not really necessary to look at the problem from this perspective.
Regarding bulk density and sonic velocity they indeed are part of an equation for density, which, with high speed impact, changes as gel mass is violently displaced upon impact with a high-speed bullet.
Unfortunately bullet manufacturers' published terminal ballistics data is next to useless because gel "calibration" is generally not given nor is expanded "diameter" defined. Actually, shooting JHPs into water jugs and measuring impact velocity and average recovered diameter would provide more information about suitability of such for self-defense than most gel tests on the Internet -- especially tests with that "clear, inconsistent and low-density stuff."
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481
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Not all manufacturers' gelatin testing is "useless"; Brenneke's gelatin test being one such notable instance.
In the example provided earlier in post #225—
https://www.thehighroad.org/index.php?threads/a-gel-expert-explains.857971/page-9#post-11316459
—BB calibration in each block can be seen in the images and the projectile's expanded diameter is defined.
The Wolberg paper from early '90s is anything but convincing evidence of equivalence between penetration in standard 10% ordnance gel and human soft tissue. Firstly, that data was only based on some 28 shootings or so with unknown bullet paths and unknown tissue involvement. For all we know most of those fatal shots could have substantially included low-density lung tissue. Furthermore, Wolberg apparently promised to IWBA to provide additional data from more shootings and that apparently never materialized. Although penetration overall was similar, on average, in those limited cases, compared to average penetration in gel -- it was only because average bullet expansion was about 17% (area) less in the bullets recovered from bodies; meaning average forces on bullets in those bodies were significantly greater than average forces would be exerted in gel on same bullets. Furthermore, when recovered average bullet diameters from bodies were about the same as in gel, resultant penetration in bodies was about 2.6" less (at least twice). Since there is no guarantee that a JHP which impacts a body will expand less than such JHP would expand in gel, it is likely, as Wolberg's data suggests, that penetration in just soft tissues in a body would be significantly less than penetration in standard 10% ordnance gel.
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C-grunt
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This has run so far off into the weeds that it's absurd.
Ballistic gel is meant to be a consistent test medium to test cartridges/bullets against each other. It's meant to simulate human tissue. Whichever exact tissue or thickness or viscosity or USDA meat rating it has doesnt matter. The pass and fail criteria was set because of real world shooting analysis. Bullets that pass the testing have very good street records. Bullets that fail the testing have more instances of failure in real world use.
Ballistic gel is meant to be a consistent test medium to test cartridges/bullets against each other. It's meant to simulate human tissue. Whichever exact tissue or thickness or viscosity or USDA meat rating it has doesnt matter. The pass and fail criteria was set because of real world shooting analysis. Bullets that pass the testing have very good street records. Bullets that fail the testing have more instances of failure in real world use.
In order for ballistic gel to simulate human tissue ( JHP expansion and penetration) density of ballistic gel must be close to that of tissue and viscosity of the gel must be such that viscous forces on the bullet in the gel are close to shear/tensile/compressive forces exerted on same bullet in tissue. If not, simulation of gel to tissue is not valid.
It certainly can be 1:1 "analog" as far as JHP expansion and penetration are concerned if inertial and non-inertial forces in gel and tissue are matched.
C-grunt
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Anything penetrated by any bullet exerts a force on such bullet -- the relevant forces exerted by a body on a bullet can be approximated by forces exerted on same bullet in a proper simulant, at least as far as penetration and expansion is concerned. Actually, the FBI specified 12" minimum penetration and up to 18" of soft tissue penetration is better -- so since most of us are not allowed to experiment shooting people, proper simulant is helpful as a guide to meet that penetration criterion.
C-grunt
Member
There is no reason, in principle, why forces exerted on a bullet in appropriate gel cannot be matched to forces exerted on same bullet in a body (penetration/expansion purposes) -- once the latter forces are known or closely approximated. BB at 590 fps penetrates 3.35" of muscle tissue with skin, though granted that's not the case with all soft tissues (hence the problem with 10% standard ordnance gel as a valid simulant).
C-grunt
Member
I have not shot a person with a BB impacting @ 590 fps; however, I accept Fackler's and MacPherson's statement that such a BB shot into a pig muscle tissue on average penetrates 3.35". Incidentally, U.S. Consumer Safety Commission has reports of about 4 deaths per year caused by BB guns or pellet guns -- and most likely those unfortunate deaths were a result of several inches of tissue penetration.
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Overall disruption of the ballistic gel along the entire bullet path by a given round is both interesting and very meaningful.
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You misunderstood. I would probably be the last person here to "directly correlate/correspond" disruption in 10% ordnance gelatin to damage done in the human body and no such direct correlation was even suggested by my statement. In fact, it is precisely because of the lack of such direct correlation that I consider overall disruption by a bullet in a gel very meaningful -- and not just the "permanent cavity" in a gel.
Lethality of BB and pellet guns, whereby several inches of tissue was penetrated after penetrating skin first of course, is well known. As previously mentioned, U.S. Consumer Safety Commision reports about 4 deaths from such each year. Your "testing" may vary, of course. Incidentally, I do not disagree that a BB that penetrates only an inch or two in a standard gel will bounce off skin -- but then such BB is not impacting standard gel or skin @ 590 fps..........
Double Naught Spy
Sus Venator
Actually, in properly prepared wet pack, the "permanent cavity" is what matters because of better correlation of tensile/shear forces in properly prepared wet pack and tissue overall.Well time to break out the old wet pack of magazines. They have a strong lack of direct correlation and so should be exceptionally meaningful.
481
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It is true that there is no direct correlation between the amount of (mass) gel disruption and the amount of tissue disruption by a given bullet; what is not true is that velocity of a given bullet penetrating tissue is not relevant in its ability to disrupt tissue. In fact, velocity is the only quantity that enables a bullet to disrupt tissue (for given bullet shape); inadequate velocity -- no penetration "work".
RetiredUSNChief
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We're beating a dead horse here.
Ballistics gel is not supposed to "replicate" human tissue...it was never intended to. It's far too complex an issue to do this for a wide variety of reasons, not the least of which is the simple fact that human tissue parameters vary from person to person.
It's supposed to provide a broad, homogeneous simulation of soft human tissue which is easily duplicated in a standardized, or "calibrated", format by which the subject of projectile penetration (and expansion/deformation) can be measured through it and compared across a broad range of bullet calibers, designs, and velocities.
THAT'S IT.
Terminal ballistics is an extremely complicated issue with far too many variables to consider when trying to gather meaningful information and make correlations.
SO...when talking about ballistic gel:
STOP talking about skin. There is no "skin" on ballistics gel and that variable is not taken into account when using gel, nor can you put a "skin" on it and say "this represents skin", because skin is different from person to person and from one angle of incident to another. Even if you had "skin" on it, it wouldn't be representative of all the possible variables you could have, and therefore people would STILL argue about it.
STOP talking about disruption. That's another false path to go down, because not only is ballistic gel homogeneous, it's also not intended to replicate specific tissue elasticity, specific tissue density variations, specific tensile strengths, etc. And even if it did, people would STILL argue about it.
STOP talking about bone, how a person doesn't have "12 inches of soft tissue", and all that other stuff. There is no bone, no layers of simulated fat and muscle tissues, no organs, etc.
It's an easily standardized/calibrated homogeneous medium which ONLY SIMULATES the average density of human soft tissue by which bullet performance with respect to simple penetration and expansion capabilities IN THAT MEDIUM can be MEASURED and COMPARED in a repeatable fashion.
From this, you can gather information which can be used to decide if a bullet is LIKELY to be CAPABLE of penetrating deeply enough into soft human tissue to reach vital organs AND that a specific bullet design will or will not be likely to, for example, expand as designed.
KEY WORD in that last: LIKELY.
Ballistics gel is not supposed to "replicate" human tissue...it was never intended to. It's far too complex an issue to do this for a wide variety of reasons, not the least of which is the simple fact that human tissue parameters vary from person to person.
It's supposed to provide a broad, homogeneous simulation of soft human tissue which is easily duplicated in a standardized, or "calibrated", format by which the subject of projectile penetration (and expansion/deformation) can be measured through it and compared across a broad range of bullet calibers, designs, and velocities.
THAT'S IT.
Terminal ballistics is an extremely complicated issue with far too many variables to consider when trying to gather meaningful information and make correlations.
SO...when talking about ballistic gel:
STOP talking about skin. There is no "skin" on ballistics gel and that variable is not taken into account when using gel, nor can you put a "skin" on it and say "this represents skin", because skin is different from person to person and from one angle of incident to another. Even if you had "skin" on it, it wouldn't be representative of all the possible variables you could have, and therefore people would STILL argue about it.
STOP talking about disruption. That's another false path to go down, because not only is ballistic gel homogeneous, it's also not intended to replicate specific tissue elasticity, specific tissue density variations, specific tensile strengths, etc. And even if it did, people would STILL argue about it.
STOP talking about bone, how a person doesn't have "12 inches of soft tissue", and all that other stuff. There is no bone, no layers of simulated fat and muscle tissues, no organs, etc.
It's an easily standardized/calibrated homogeneous medium which ONLY SIMULATES the average density of human soft tissue by which bullet performance with respect to simple penetration and expansion capabilities IN THAT MEDIUM can be MEASURED and COMPARED in a repeatable fashion.
From this, you can gather information which can be used to decide if a bullet is LIKELY to be CAPABLE of penetrating deeply enough into soft human tissue to reach vital organs AND that a specific bullet design will or will not be likely to, for example, expand as designed.
KEY WORD in that last: LIKELY.
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