.38 double wadcutter load

[the Schwartz]

.38 WC example You can't use Brassfetcher's recovered diameter/weight from gel shots in the expedient equation.

Actually, you could, but you would need the correctly fitted "alpha" exponent to do so. If projectile expansion/deformation were uniform, it might be possible to use the exponent (which acts much like a drag coefficient in the mTHOR power law) for an expanded JHP, but for a projectile whose expansion profile differs greatly from an expanded JHP, a new/different exponent would certainly be required. The same can be done with the Q-model with an equal proviso for using a new/different/correct C_D if/where required.

To amplify further upon the point that you have made here—

.38 WC example You can't use Brassfetcher's recovered diameter/weight from gel shots in the expedient equation. For non expanding projectiles, the expedient equation uses projectile specs and chrono readings, for expanding rounds it uses recovered weights/diameters from water, not gel, and chrono readings. The whole point of the expedient equation is to use water for a testing medium and make predictions of performance in 10% gel.

Both equations (the "Q-model" and the "mTHOR model")—and MacPherson's equation—can be used to predict the maximum terminal penetration of non-expanding projectiles without testing, but testing is ALWAYS highly recommended. While non-expanding designs typically do not expand in water or 10% gelatin, that possibility does exist, and they should be tested at some point to confirm their actual behavior in either test medium.

All three models ("Q", "mTHOR", and MacPherson) can be used as heuristic tools bearing in mind that their respective predictions are just that—they are predictions!

The predictions made by all three mathematical bullet penetration models also rely upon certain assumptions/presumptions:

1. that the projectile maintains a 'nose-forward attitude' throughout the entirety of the penetration event being modeled
2. that expansion of the projectile—if it occurs—is uniform and consistent
3. that the projectile does not disintegrate or fragment completely and,
4. that the projectiles and test mediums are all perfectly isotropic

In reality, neither projectiles nor test mediums are perfectly isotropic in their respective construction. Microscopic variations in the materials composing the projectile and minimal fluctuations in individual projectiles arising from varying tolerances the manufacturing process—which does not produce perfectly identical projectiles in the first place—in addition to the imperfect isotropic nature of valid test mediums, contributes to the variations in terminal expansion and penetration depths observed when any given projectile construction is actually tested in gelatin or water test mediums.

Since you have brought it up here—

Validity with multi-projectiles hitting gel at the same time?

Since this started, I've wondered about the validity of using models developed for a single project for a duplex load. Part of the reason I keep asking about actual testing with a valid tissue simulant instead of "paper" predictions. However, theSchwartz and you seem to think it's OK to apply here so I haven't expressed it until now. You express doubts about it's use on a 00 load with 8/9 projectiles, but have no issues with 2 projectile load? Why does it work with 2 but not 8/9? Maybe your "drafting" is because you're using Clear Gel that overstates penetration compared to 10% gel and your model predicts performance in 10% gel. Or you are using a single projectile model that doesn't apply to multiple projectile loads.

—I'll clarify my thoughts (simply because no one has mentioned it until now ) regarding the use of these bullet penetration models to make predictions for multiple projectiles striking a target simultaneously...

None of the simple mathematical bullet penetration equations presently under discussion here (namely, the "Q", "mTHOR", and MacPherson models) are really capable of accurately modeling the behavior of multiple projectiles in simultaneous penetration events. Multiple projectiles striking a target simultaneously create enormously complicated challenges (temporary and permanent cavities that may or may not intersect wholly or partially—theorized as 'drafting' in earlier posts by pettypace, non-uniform expansion, etc.) that these mathematical bullet penetration models simply cannot account for. Complex multi-projectile modeling can be accomplished through the use of multi-physics FEM suites like ANSYS and LS-DYNA, but those options are far beyond the grasp and processor-power of "ordinary, average guys" (like us) wishing to investigate the potential terminal performance of multiple projectile loads. Such theorizing is certainly one of the more attractive utilities of eloquent equations like the "Q", "mTHOR", and MacPherson models because running FEM computations ''by hand'' on a scientific calculator would literally take months (or even years!) to complete for just one prediction. Ultimately, as I have said before, testing in a valid medium* is ALWAYS highly recommended.

Short of using FEM software, these simple equations are the best that we have.



*My opinion of the Clear Ballistics Gel product, and all other ''as-yet unproven synthetic test mediums'', is clear and well-known (at least here anyway), so I'll not waste further bandwidth restating it here.

[SiriusBlunder]

Actually, you could, but you would need the correct (''fitted") "alpha" exponent to do so. If projectile expansion/deformation were uniform, it might be possible to use the exponent (which acts much like a drag coefficient in the mTHOR power law) for an expanded JHP, but for a projectile whose expansion profile differs greatly from an expanded JHP, a new/different exponent would be required. The same can be done with the Q-model with an equal proviso for using a new/different/correct C_D if/where required.

"You can't" was in the context of the OP using the existing parameters with gel results.

What situation would you see using gel to get recovered weights/diameters to plug into an equation to make a prediction of penetration in gel advantageous or was this just a thought exercise?

Both equations (the "Q-model" and the "mTHOR model")—and MacPherson's equation—can be used to predict the maximum terminal penetration of non-expanding projectiles without testing, but testing is ALWAYS highly recommended. While non-expanding designs typically do not expand in water or 10% gelatin, that possibility does exist, and they should be tested at some point to confirm their actual behavior in either test medium.

A few times I've seen minor deformation/expansion of TMJ rounds and hard-cast WCs fired into water, but I agree they typically don't.

All three models ("Q", "mTHOR", and MacPherson) can be used as heuristic tools bearing in mind that their respective predictions are just that—they are predictions!

We use mThor when we randomly test a round from each box in our cases of carry ammo. Results are close enough to expected results (DocGKR ) for us to feel a little warm and fuzzy that the lot of ammo is OK.

—I'll clarify my thoughts (simply because no one has mentioned it until now ) regarding the use of these bullet penetration models to make predictions for multiple projectiles striking a target simultaneously:

None of the simple mathematical bullet penetration equations presently under discussion here (namely, the "Q", "mTHOR", and MacPherson models) are really capable of accurately modeling the behavior of multiple projectiles in simultaneous penetration events.

Thanks for the clarification. I got the impression from comments made here or at Cast Boolits by the OP about PM communication with you that using mThor for a duplex load was valid. My bad for not getting confirmation by asking you directly before making that statement. I apologize if my presumption was offensive.

*My opinion of the Clear Ballistics Gel product, and all other ''as-yet unproven synthetic test mediums'', is clear and well-known (at least here anyway), so I'll not waste further bandwidth restating it here.

Thanks for continuing to help keep the Clear Gel folks here "honest".

[the Schwartz]

"You can't" was in the context of the OP using the existing parameters with gel results.

What situation would you see using gel to get recovered weights/diameters to plug into an equation to make a prediction of penetration in gel advantageous or was this just a thought exercise?

There would be extremely limited value in undertaking such an effort. I was never tempted to pursue it for the modeling in the book. Non-expanding designs (wadcutters, FMJs, spherical shot, pellets, etc.) typically deform asymmetrically under complex material failure modes (that border on being nearly unrepeatable) because their deformation is governed by their internal geometry and metallurgical micro-structure which is not designed to (re)direct the hydro-dynamic forces to ensure uniform expansion like what we see in the expansion cavities of JHPs. FEM suites can handle those complex material failure modes far more more accurately than the simple penetration equations ("Q", "mTHOR", and MacPherson) we are using here.

A few times I've seen minor deformation/expansion of TMJ rounds and hard-cast WCs fired into water, but I agree they typically don't.

Agreed, it is a rare and unpredictable phenomenon.

We use mThor when we randomly test a round from each box in our cases of carry ammo. Results are close enough to expected results (DocGKR ) for us to feel a little warm and fuzzy that the lot of ammo is OK.

The main objective of Quantitative Ammunition Selection was to provide a reasonably accurate, yet ''easy-to-understand'', test methodology that allows we mere mortals (and under-funded LE agencies) the ability to use a scientifically-valid process employing a valid tissue simulant (H₂O) evaluate our self-defense ammunition while reducing the technical burden needed to do so.

Thanks for the clarification. I got the impression from comments made here or at Cast Boolits by the OP about PM communication with you that using mThor for a duplex load was valid. My bad for not getting confirmation by asking you directly before making that statement. I apologize if my presumption was offensive.

No worries, DM! I always view these exchanges as opportunities to ''set the record straight'' and value the dialogue. We are ''good''.

Thanks for continuing to help keep the Clear Gel folks here "honest".

If by "Clear Gel folks" you are referring to the manufacturers of those products, then, yes, I'll never stop doing so.

The manufacturers of these unproven synthetic "tissue simulants" have done serious disservice and continue to do damage to the industry with their shameless exploitation of the general public's misunderstanding of the technology. The synthetic gelatin manufacturers have flooded the market with products that fail to represent accurately the terminal ballistic behavior and there is, as Doc has noted in the past, almost no valid information to be found on the internet these days. We can thank the manufacturers of these products for the absolute ''tidal wave'' of invalid Clear Ballistics Gel tests washing across the internet these days.

On the other hand, I absolutely detest seeing the general public—and my fellow shooting enthusiasts—being exploited by these manufacturers just to make a few dollars.

[pettypace]

None of the simple mathematical bullet penetration equations presently under discussion here (namely, the "Q", "mTHOR", and MacPherson models) are really capable of accurately modeling the behavior of multiple projectiles in simultaneous penetration events. Multiple projectiles striking a target simultaneously create enormously complicated challenges (temporary and permanent cavities that may or may not intersect wholly or partially—theorized as 'drafting' in earlier posts by pettypace, non-uniform expansion, etc.) that these mathematical bullet penetration models simply cannot account for.

Given what you know about the physical characteristics of the simulant, the laws of physics, and the commotion created within the gel by the passage of the projectiles, can you imagine any possible way that two simultaneous projectiles (let's stipulate non-expanding and non-tumbling) would have less penetration than a single projectile of the same configuration at the same velocity?

What I'm getting at, of course, is my belief that the penetration models, while incapable of predicting the actual penetrations, remain, nevertheless, perfectly capable of predicting a minimum penetration. What's your take on that?

[pettypace]

If you're happy with <= 13'' of predicted penetration in BG of non expanding, non barrier blind projectiles, rock on.

Assuming the quote above is a good-willed attempt to promote the technical discussion and not just a thinly veiled ad hominem potshot, I'll try to briefly address it point by point:

1) Nope, not happy with " <= 13'' of predicted penetration" . That leaves the short side wide open. Changing that to >=13" would make me happier.

2) Yes, I'm perfectly happy with "non expanding." My focus has been on two projectiles in a .38 Special case fired from a 2" barrel. At least one of the projectiles really "wants" to be a wadcutter which should be hard and sharp. None of that leaves room for expansion. But who cares? If cross-sectional area is a virtue, then two .36 caliber projectiles, assuming they separate, already have .50 caliber worth.

3) Nope, not happy with "non barrier blind." But your quote implies that a two-projectile load would necessarily be non barrier blind. Is that just an assumption or is it based on some testing data you're willing to share?

[SiriusBlunder]

3) Nope, not happy with "non barrier blind." But your quote implies that a two-projectile load would necessarily be non barrier blind. Is that just an assumption or is it based on some testing data you're willing to share?

"Barrier Blind" does not mean a projectile will pass through a barrier, it means it will penetrate adequately after passing through the barrier, as if the barrier wasn't there. If a non expanding projectile barely penetrates adequately in BG, I don't see how adding a hard barrier like AG will make it perform better, but would change my mind if shown evidence. (Some will argue that "barrier blind" means the "same" or "similar" without the barrier, I don't think any round performs exactly the same, but I'm not sure getting into a semantic debate is valuable. "Adequate" is what's important).

So technically it's an assumption as I don't know of any testing of .36 cal, 110 gr @ 650 projectiles, but it's sort of a statement of fact since the proposed load is predicted to barely penetrate adequately in BG. Actually, this whole thread is based on assumptions as there is no valid model or valid testing of this load.

Recall, my first reaction to your proposed load was "sounds like an anemic .380 ACP so I doubt it performs well".

.380 ACP is not known for fairing well against auto glass.

I'm not going to look for lots of testing with .380 ACP and AG, but here is one from Lehigh Defense and their Extreme Penetrator round which is a monolithic, non expanding design and touted as "barrier blind". Take it for what's it's worth.

.380 ACP, 85 grain @ 800 FPS
4LD: 17''
auto glass: 7''
https://www.youtube.com/watch?v=7tujq9nMCR0

I would say that's not the same or similar. What's important is that it comes no where near adequate penetration after AG. I'm not aware of any .380 ACP load that passes the AG test, I've heard Corbon DPX gets close (@ 1050 fps), and would love to hear differently.

At least around here, .380 ACP is considered the floor for a self defense semi because it will reliably break bone. I don't see how a load that's significantly less powerful will perform as well, but I'm open to seeing valid testing.

[pettypace]

Thanks for all that info.

A few more questions:

1) Are there specs for the AG? Or will any old cracked windshield serve?

2) Am I right that the AG needs to be at 45 degrees to the bullet path?

3) Are there any other requirements that the backyard ballistician should keep in mind in trying to do an AG barrier test?

[the Schwartz]

Given what you know about the physical characteristics of the simulant, the laws of physics, and the commotion created within the gel by the passage of the projectiles, can you imagine any possible way that two simultaneous projectiles (let's stipulate non-expanding and non-tumbling) would have less penetration than a single projectile of the same configuration at the same velocity?

Yes.

There are ''real-world'' examples of the clear polymer product being sold by Clear Ballistics under-representing terminal penetration depth on the 'net, like this one (seen from 0:08 to 0:12 in the video)—

https://www.youtube.com/watch?v=czsd-v5sm3s

—that show projectiles rebounding several inches rearward and coming to rest at a depth that is far shallower than their actual maximum penetration depth.

In the specific case cited, the test projectile reaches its maximum penetration depth of 18 inches in the Clear Ballistics polymer product at 8 seconds into the video—



—and then rebounds inside the temporary cavity to a depth of 13.5 inches where it remains at rest at 12 seconds into the video—



—having rebounded 4.5 inches(!) which is a reduction of 25% of its maximum penetration depth seen at the 8-second mark in the video.

In all honesty, I doubt that I, or anyone else other than the manufacturer, knows very much about the clear polymer product being sold by Clear Ballistics, Inc. According to their technical data relating to their "10% Ballistic Gelatin FBI Block" they list its dimensions as being 40.64 cm in length, 15.24 cm in width, 15.24 cm in height and its mass as being 8.16 kg or 8,160 grams which—if you do the math—gives their product an advertised mass density of 0.8645 grams per cubic centimeter. I am personally aware of other research that has found the density Clear Ballistics polymer product to be as low as 0.790 g/cm³ and as high as 0.824 g/cm³—both of those being much lower density values than the manufacturer's claimed density of 0.8645 g/cm³—it's all over the place. I am not sure who to believe, or that it is even worth bothering with.

On the other hand, we know a lot about 10% ordnance gelatin, water, 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

For the Clear Ballistics polymer product we have: c = unknown; ρ = 790 kg/m³, 824 kg/m³, and 864.5 kg/m³; K = unknown

What I'm getting at, of course, is my belief that the penetration models, while incapable of predicting the actual penetrations, remain, nevertheless, perfectly capable of predicting a minimum penetration. What's your take on that?

I am not sure that that is the case.

None of the bullet penetration models—the Q-model, the mTHOR model, or the MacPherson model—are applicable to the terminal ballistic behavior of projectiles observed in any of the clear polymer products being sold by Clear Ballistics, Inc. For that reason, I am disinclined to engage in conjecture about to their respective validity when compared to test data obtained in that material. There are too many "unknowns" in conjunction with the clear polymer product manufacturer constantly making frequent, unpredictable changes to their product's formulation and its material-physical properties. Other than for the sake of "having fun" and/or ''just horsing around and shooting stuff", there is no real value to be obtained from shooting the Clear Ballistics polymer product. It is, in my opinion, also a waste of time trying to figure out a way to make any of the bullet penetration models apply to data obtained from the Clear Ballistics polymer product.

[SiriusBlunder]

Thanks for all that info.

A few more questions:

1) Are there specs for the AG? Or will any old cracked windshield serve?

2) Am I right that the AG needs to be at 45 degrees to the bullet path?

3) Are there any other requirements that the backyard ballistician should keep in mind in trying to do an AG barrier test?

You're welcome.

There are specs to the glass and a compound angle involved. I believe this info is current, but would search for official specs to make sure.

Brassfetcher has a page on the tests and may have tips and practical ideas some where on his site.

[pettypace]

None of the bullet penetration models—the Q-model, the mTHOR model, or the MacPherson model—are applicable to the terminal ballistic behavior of projectiles observed in any of the clear polymer products being sold by Clear Ballistics, Inc. For that reason, I am disinclined to engage in conjecture about to their respective validity when compared to test data obtained in that material. There are too many "unknowns" in conjunction with the clear polymer product manufacturer constantly making frequent, unpredictable changes to their product's formulation and its material-physical properties. Other than for the sake of "having fun" and/or ''just horsing around and shooting stuff", there is no real value to be obtained from shooting the Clear Ballistics polymer product. It is, in my opinion, also a waste of time trying to figure out a way to make any of the bullet penetration models apply to data obtained from the Clear Ballistics polymer product.

Thanks for the reply.

But I have to apologize for not being clear (no pun intended) in asking my question. No, I was asking about validated 10% ordinance gel. No Clear Ballistic product involved.

For example, the mTHOR model predicts a .36 caliber 110 grain WC at 650 ft/s will penetrate about 13" of validated 10% ordinance gel. So, can you think of any reason that 13" couldn't be considered the absolute minimum predicted penetration for two .36 caliber 110 grain WCs fired simultaneously at 650 ft/s into the same validated 10% ordinance gel?