No. Both he & Charles Schwartz are wealths of information who know more about wound ballistics than I likely every will and they have been very generous in freely sharing their knowledge with us. I just suspect both are more concerned about defending consumers from charlatans than acknowledging, investigating, & correcting the flaws remaining in traditional testing.
As proof of those lingering flaws I gave the example of 1 bullet design, out of the hundreds Dr. Roberts has reviewed, that performed exceptionally well in his tests but failed so miserably in the real world it was recalled & tweaked before rerelease.
Last edited by 0ddl0t; 11-16-2019 at 08:13 AM.
Thanks for this post. You don't even have to check the math to see your point, it's pretty clear and well laid out.
And thanks to @DocGKR also for pointing out that the search goes on for better test mediums.
I've been a ballistic geek wannabe since the '80s...
I knew I'd read the above somewhere, but it took me until now to find the source:
Penetration of a 9mm bullet at 1000 ft/sec is resisted by an inertial force of about 800 pounds; it is obvious that the presence or absence of a 3 to 5 pound shear force makes no practical difference in the penetration at this velocity. This also explains why the fact that gelatin fractures more easily than tissue does is not important.
The extension of these dynamics to soft tissue variation is obvious. Different types of tissue present different resistance to finger probing by a surgeon, but the surgeon is not probing at 1000 ft/sec. Different tissue types do have differences in the amount of shear force they will support, but all of these forces are so small relative to inertial forces that there is no practical difference. The tissue types are closer to one another than they are to water, and bullet expansion in water and tissue are nearly identical at velocities over 600 ft/sec where all bullet expansion takes place (See Bullet Penetration for a detailed explanation of bullet expansion dynamics).
Since inertial forces depend on accelerating mass, it makes sense that these forces should be lower at lower velocities (because the penetrated material cannot be accelerated to a velocity higher than the bullet). Shear forces have little velocity dependence, and as a result, shear forces are a much larger fraction of the total when bullet velocity is below the cavitation threshold. This low velocity effect is the reason that total bullet penetration depth is much different in water and in tissue or a valid tissue simulant.
As a result of the penetration dynamics, most soft solids with a density very near soft tissues (i.e., near the density of water) are satisfactory tissue simulants when shear forces are not important. However, total penetration depth depends significantly on dynamics at velocities below 400 ft/sec, so most materials do not properly simulate penetration depth. The total bullet penetration depth in tissue and a valid tissue simulant should be the same; standard practice is to use calibrated gelatin to insure this. In effect, gelatin calibration is done to ensure that the shear forces in the gelatin are the same as in typical soft tissue (as described in Bullet Penetration, the technical parameter used in the dynamic is viscosity).
-- “Wound Ballistics Misconceptions.” (Duncan MacPherson, Wound Ballistics Review, 2(3): 1996; 42-43)
...Just posting for those lurking 3rd parties with open minds...
The bolded portion of the quoted text—
—does not affirm the validity of relying upon "lower-than-water-density" test mediums. In fact, because they misrepresent maximum terminal penetration depth, the bolded text that you've quoted above is actually an indictment of the use of "lower-than-water-density" test mediums since the accurate representation of maximum terminal penetration depth is one of the most important metrics considered when undertaking such testing.
More specifically, the mass densities of the clear, synthetic gel (790 - 824 kg/m³), butter, margarine, and mozzarella cheese are all far enough below that of water that they do not qualify as having "a density very near soft tissues" or "near the density of water". If anyone wishes to substantiate the dynamic equivalence of these "alternative test mediums", then it is incumbent upon those claiming "validity" to support that position. This is easily accomplished by supplying the respective bulk moduli (K), mass densities (ρ), and internal sonic velocities (c) so that the respective physical properties of these "alternative test mediums" may be evaluated against those of human soft tissue (c = 1,540 ms-1, ρ = 1,020 kg/m³, K = 2.42 GPa) using the physical relationship that is set forth in the Newton-LaPlace formula: c = √(K/ρ) .
Of course, you are free to provide the respective mass-densities, bulk moduli, and internal sonic velocities of these "alternative test mediums" in support of your assertion that they are indeed "valid".
If you cannot support your assertion with these physical parameters, then all you are really doing is debating in a vacuum.
Last edited by the Schwartz; 11-16-2019 at 01:17 PM.
''Politics is for the present, but an equation is for eternity.'' ―Albert Einstein
Full disclosure per the Pistol-Forum CoC: I am the author of Quantitative Ammunition Selection.
Additionallly, submitted for the consideration of those "lurking 3rd parties with open minds", they might also wish to bear in mind that the next line after that which has been bolded in black, which has now been set in bold red, also affirms that "the total bullet penetration depth in tissue and a valid tissue simulant should be the same" and that "standard practice is to use calibrated gelatin to insure this".
Finally, if the proper representation of total bullet penetration depth is not desired, anyone can simply fire bullets into water to cause them to expand. There is no need to "reinvent the wheel" when water (which already possesses the requisite physical properties) is so easy to use and meets the requirement for being "near the density of water" or having "a density very near soft tissues".
Last edited by the Schwartz; 11-16-2019 at 01:54 PM.
''Politics is for the present, but an equation is for eternity.'' ―Albert Einstein
Full disclosure per the Pistol-Forum CoC: I am the author of Quantitative Ammunition Selection.
Straw man again... No one here is arguing about obtaining valid penetration data from other media.
Patently false.More specifically, the mass densities of the clear, synthetic gel (790 - 824 kg/m³), butter, margarine, and mozzarella cheese are all far enough below that of water that they do not qualify as having "a density very near soft tissues"
Lung (inflated): 255-604 kg/m^3
Fat: 812-964 kg/m^3
Connective tissue 911-1142
Blood is 1050
Lung (deflated): 1050
Cartilage is 1100
Intervertebral disc 1100
Larynx 1100
Bronchi 1050-1147
Liver 1050-1158
Muscle 1041-1178
https://itis.swiss/virtual-populatio...abase/density/
Rubbing alcohol 790
Ammonia (max concentration) 880
Butter is 911
Cream chesse is 966
Jello is 980-1050
Milk is 1030
Orange juice is 1050-1125
potato 1090
mozzarella is 1100
Bleach (12.5%) 1200
Salt water (saturated) 1360
Bullets traveling just over their expansion thresholds for living tissue will expand readily in water, even if they are inconsistent in tissue.
But if a bullet expands in both rubbing alcohol and bleach - now you can be a bit more confident in the robustness of expansion through the variety of tissue densities it might encounter.
Last edited by 0ddl0t; 11-16-2019 at 02:15 PM.
What is the point of any of this?
Terminal ballistic testing conducted in an uncontrolled/uncorrelated medium produces expansion and penetration data that is only comparable within the uncontrolled/uncorrelated medium and that is incomparable to all other mediums.
It is interesting to note that you continue to refuse to provide the other requisite physical parameters (that is, the respective bulk moduli, internal sonic velocities of butter, margarine, mozzarella cheese) required to support your claim that any of these—
—are valid terminal ballistic test mediums.
Once again, mass-density is just one part of the the Newton-LaPlace formula: c = √(K/ρ) . You'll need to provide all of the requisite physical properties of these "alternative mediums" to prove that they possess the dynamic equivalent qualities specified by the Newton-LaPlace formula so that they yield data comparable to other mediums.
No, you cannot. What occurs in those mediums applies only within those mediums.
All that you have done so far is post the densities of various substances and refused to provide the physical parameters that would confirm their dynamic equivalence to any other medium (or human soft tissue) and support your claims.
Last edited by the Schwartz; 11-16-2019 at 03:29 PM.
''Politics is for the present, but an equation is for eternity.'' ―Albert Einstein
Full disclosure per the Pistol-Forum CoC: I am the author of Quantitative Ammunition Selection.