Ballistic gelatin comparisons: Part I

[0ddl0t]

A bullet out of it's designed speed envelope isn't going to work as designed. The answer isn't that somehow short barrels need different testing methods. The answer is to test the bullets in the same fps range that they leave the shorter/longer barrel from in the same protocols that "normal" barrel lengths are tested at, which is done.

If the test was all encompassing & perfect, sure. In reality it is not.

Because almost all defensive ammo is designed to perform robustly from duty pistols, and almost all the professional testing involves duty ammo from duty pistols, the flaws in the existing gel tests aren't as apparent because none of the ammo is squeaking by at the edges of their performance envelopes.

Start playing around at the boundaries and you realize the existing tests might not offer as much cushion & clarity as you'd like.

I get the sense that you are attempting to make a point, but "moving the goal posts" in terms of the subject (test mediums ===> barriers) being discussed makes whatever point you are attempting difficult to discern.

My point is that the existing tests of 10% gel & 10% gel behind 4 layers of denim are imperfect for many of the popular concealed carry guns on the market. Repeatable tests in other media or with alternate intermediate barriers can illustrate real deficiencies left uncovered by these traditional tests.

As an example, I give the gold dot 147 from a 3" barrel which is on Doc's list of recommended ammo and which reliably expands in traditional testing with 10% ordnance gel. But if you lower ρ (using lower density media) or V (by adding distance, barriers, etc) even slightly it begins to fail to expand.

That gold dot 147s are at the lower bounds of their performance window from a 3" barrel is useful information to know & that information can be reliably and repeatedly discerned from non traditional (but scientifically valid) tests.

[BehindBlueI's]

If the test was all encompassing & perfect, sure. In reality it is not.

Because almost all defensive ammo is designed to perform robustly from duty pistols, and almost all the professional testing involves duty ammo from duty pistols, the flaws in the existing gel tests aren't as apparent because none of the ammo is squeaking by at the edges of their performance envelopes.

Start playing around at the boundaries and you realize the existing tests might not offer as much cushion & clarity as you'd like.

Even if we accept that as fact, the answer is to repeat the protocol that's proven to correlate to the real world but at the fps you find from the shorter/longer barrel. The answer is not to shoot melons or pudding filled pinatas or whatever.

[KellyinAvon]

Even if we accept that as fact, the answer is to repeat the protocol that's proven to correlate to the real world but at the fps you find from the shorter/longer barrel. The answer is not to shoot melons or pudding filled pinatas or whatever.

Suddenly I'm getting the urge to fill a pinata with pudding, and shoot it. I thinking shoot it with a deer slug. I don't remember reading anything at my local range that this is specifically forbidden.

[the Schwartz]

My point is that the existing tests of 10% gel & 10% gel behind 4 layers of denim are imperfect for many of the popular concealed carry guns on the market. Repeatable tests in other media or with alternate intermediate barriers can illustrate real deficiencies left uncovered by these traditional tests.

As an example, I give the gold dot 147 from a 3" barrel which is on Doc's list of recommended ammo and which reliably expands in traditional testing with 10% ordnance gel. But if you lower ρ (using lower density media) or V (by adding distance, barriers, etc) even slightly it begins to fail to expand.

That gold dot 147s are at the lower bounds of their performance window from a 3" barrel is useful information to know & that information can be reliably and repeatedly discerned from non traditional (but scientifically valid) tests.

What, specifically, are the materials (that is, what test medium?) used in these "non-traditional (but scientifically valid) tests"?

[the Schwartz]

Suddenly I'm getting the urge to fill a pinata with pudding, and shoot it. I thinking shoot it with a deer slug. I don't remember reading anything at my local range that this is specifically forbidden.

If you do this, please post video. And make it vanilla pudding. I hate vanilla pudding so it's got it comin'.

[DocGKR]

Note that virtually every decent ballistic test facility that conducts valid research has frequently experimented with a variety of simulants to determine if something has been developed which is superior to the current 10% ordnance gel or has a better correlation with living tissue.....so far nothing better has been discovered.

[0ddl0t]

Even if we accept that as fact, the answer is to repeat the protocol that's proven to correlate to the real world but at the fps you find from the shorter/longer barrel. The answer is not to shoot melons or pudding filled pinatas or whatever.

Doing the same thing over and over and expecting different results is insanity.

And that whole "proven correlation" is mildly overstated. Best I can tell it comes from a study of 28 Winchester bullets recovered at autopsy in San Diego from 1987-1991. But the study excluded any bullet that left the body or hit bone which means the sample pretty much self-selected only the bullets that expanded properly.

I don't have the exact numbers to run a correlation check because the author just gave a summary of the gel test: 20 shots varying from 12-14" penetration with a ratio of 1.20 But he did list all the individual bullets from autopsy, which varied from 10-17" in penetration and ratios of 0.85-1.43.

To quote the author (Gene Wolberg):

"Shots fired into correctly prepared gelatin tissue simulant can be a valuable guideline in the selection of police ammunition. It is most useful in separating out the grossly inadequate bullets: those that penetrate only 6 or 7 inches or SP/HP that do not expand adequately."

For a rough correlation comparison, here is BrassFetcher's data comparing penetration in clear and organic gel:

cal....OG...CB
.380 7.6 9.6
9mm 13.7 13.4
357s 15.0 13.2
12gs 11.9 13.3
12g#4 11.6 11.0

Pearson Correlation Coefficient: 0.8742 (moderate-high correlation)

What, specifically, are the materials (that is, what test medium?) used in these "non-traditional (but scientifically valid) tests"?

Anything you can repeatedly use with enough consistency to be valid. You could use water mixed to a specific ratio with a less dense fluid like rubbing alcohol (or add something like salt to increase density). You could use clear gel if you can ensure consistency from one block to the next. You could use butter or margarine or mozzarella or whatever gelatinous substance you can find that is consistent from one batch to the next and has the properties you're interested in exploring.

Again the point isn't to replace ordnance gel, but to supplement it with additional data from different media.

Or you could still use ordnance gel, but stick your ammo in a sub zero freezer overnight to drop velocity ~30fps. Or heat them to 150° to add ~30fps. Or add a 5th or 6th layer of denim. Or add a 1" barrier of fat/grease barrier to ordnance gel.

As a short barrel guy, I'd be interested in lower density media and/or lower velocity testing, but a carbine guy might want to go the other way.

[Half Moon]

Suddenly I'm getting the urge to fill a pinata with pudding, and shoot it. I thinking shoot it with a deer slug. I don't remember reading anything at my local range that this is specifically forbidden.

I'm strongly feeling, for that test to be valid, Doug Mercaido from Forged In Fire needs involved:

`Your bullet, sir, will... kill`

[BehindBlueI's]

Doing the same thing over and over and expecting different results is insanity.

So your claim is that 10% gel is only good within certain fps ranges? That the results are invalid outside of those ranges? What are those ranges and how did you arrive at them?

What medium has proven correlation in those "invalid" ranges?

How did you determine that?

And that whole "proven correlation" is mildly overstated. Best I can tell it comes from a study of 28 Winchester bullets recovered at autopsy in San Diego from 1987-1991. But the study excluded any bullet that left the body or hit bone which means the sample pretty much self-selected only the bullets that expanded properly.

No, it isn't. The current FBI protocols have a proven correlation with real world OIS, with a hell of a lot bigger and more recent sample then 28 bullets from 30 years ago from the time the protocol was originally being developed.

20 shots varying from 12-14" penetration with a ratio of 1.20 But he did list all the individual bullets from autopsy, which varied from 10-17" in penetration and ratios of 0.85-1.43.

Do you think penetration is the exact same in all of the tests of the FBI protocols? That a bullet penetrates the same after going through auto glass as it does bare gel or 4LD? No. That's why there is more than one stage in the protocols. Why would you expect the same penetration in a human body every time?

[the Schwartz]

Anything you can repeatedly use with enough consistency to be valid. You could use water mixed to a specific ratio with a less dense fluid like rubbing alcohol (or add something like salt to increase density). You could use clear gel if you can ensure consistency from one block to the next. You could use butter or margarine or mozzarella or whatever gelatinous substance you can find that is consistent from one batch to the next and has the properties you're interested in exploring.

Again the point isn't to replace ordnance gel, but to supplement it with additional data from different media.

Or you could still use ordnance gel, but stick your ammo in a sub zero freezer overnight to drop velocity ~30fps. Or heat them to 150° to add ~30fps. Or add a 5th or 6th layer of denim. Or add a 1" barrier of fat/grease barrier to ordnance gel.

As a short barrel guy, I'd be interested in lower density media and/or lower velocity testing, but a carbine guy might want to go the other way.

Modeling terminal ballistic performance in human tissue is not as simple as firing bullets into a substance of a desired density and then concluding that the terminal behavior seen in that material corresponds with what occurs in a human body. Valid physical models, like 10% ordnance gelatin and water, have been shown through extensive research to correlate strongly with living tissue in terms of their material properties. Since the desired objective is to accurately represent a projectile's terminal performance in human tissue, only those specific mediums that can be shown to demonstrate the correct physical properties are valid as a means of modeling such performance. Beyond considering only the mass density of a solid test medium, a solid must also demonstrate the correct shear response within the typical magnitude of strain rates observed in such testing. Data obtained from "different media" that you've suggested above such as butter, margarine, mozzarella cheese, and for that matter, fruits, vegetables, and deli-meats, are not "supplemental" at all; in fact, they are specious and lack evidence that supports their validity as a terminal ballistic test medium that correlates with human tissue.

The clear, synthetic gel product, with its frequent changes in composition and component sourcing, is also unsuitable not only for the undocumented changes in its formulation but also for the failure of the manufacturer(s) of these products to provide information on how these changes in composition and source compare against previous iterations of their product(s).

Modeling terminal ballistic performance in fluids/liquids requires more than matching density (ρ) to achieve dynamic equivalence with soft tissue. In order to properly represent terminal performance in soft tissue, the candidate fluid/liquid must also possess the same bulk modulus (K) and internal sonic velocity (c) which are all related to one another in the Newton-LaPlace formula— c = √(K/ρ)

The internal speed of sound in isopropyl "rubbing" alcohol, C₃H₈O, is c = 1,205 ms^-1, its density is ρ = 786 kg/m³ so by extension of the Newton-LaPlace formula, its bulk modulus is K = 1.141 GPa.

Compared to the respective values of c, ρ, and K in water, 10% ordnance gelatin, and human soft tissue—

H₂O: c = 1,497 ms^-1, ρ = 999.87 kg/m³, K = 2.24 GPa
10% ordnance gelatin: c = 1,494 ms^-1, ρ = 1,040.00 kg/m³, K = 2.32 GPa
Typical values for human soft tissue: c = 1,540 ms^-1, ρ = 1,020 kg/m³, K = 2.42 GPa

—isopropyl alcohol does not compare favorably with any of these materials' values and therefore is not an acceptable candidate fluid (mixed with water or by itself) for modeling terminal ballistic response as it occurs in human tissue. No such research suggesting otherwise exists.

Due to the frequent and unknown changes in its formulation, it is also difficult to ascertain values of c, ρ, and K of the clear, synthetic gel. The only physical property of the clear, synthetic gel that is known has been subject to some variance at different times within the same source ranging from 790 kg/m³ - 824 kg/m³ with no known values for either its internal sonic velocity or bulk modulus.

Given the lack of supporting research that "ensures the consistency" of any of the "different media" that you've suggested, their use is likely to yield dubious data at best. At worst, relying on that data leads to inaccurate, and possibly dangerous, conclusions being drawn about the ammunition tested in those uncorrelated mediums.