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Thread: Cd versus Mach - common pistol bullets

  1. #1
    Site Supporter rdtompki's Avatar
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    Cd versus Mach - common pistol bullets

    I'm interested in playing around with pistol round performance at range including creating a simple ballistic model (past life experience with airborne ordinance). For example, I found an old paper on the 7.62 rifle round which contained to Cd curve, but haven't found anything OTS for pistol rounds. There is a web-based model I can play around with, but I wouldn't mind finding data for one or more common pistol bullet profiles. Any suggestions?

  2. #2
    Chasing the Horizon RJ's Avatar
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    A couple years ago, I downloaded an open source model called "Bullet".

    Name:  Screenshot from 2021-01-01 09-26-51.png
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    If that sounds like something you are interested in, let me know. I can probably re-figure out where I got it from.

  3. #3
    Site Supporter rdtompki's Avatar
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    Quote Originally Posted by RJ View Post
    A couple years ago, I downloaded an open source model called "Bullet".

    Name:  Screenshot from 2021-01-01 09-26-51.png
Views: 330
Size:  43.7 KB

    If that sounds like something you are interested in, let me know. I can probably re-figure out where I got it from.
    Thanks. I was able to find sites with that SDK available. I'm going to look more closely to see if it includes Cd data, but appears much broader in scope. The web-based model I linked to would do the trick if I overcome my laziness and enter approximate data for 9mm RN and TC bullets, for example. Does not appear the physical characteristics allowed cover defensive rounds well, but even an RN bullet might provide a good sense of short range subsonic versus longer range supersonic terminal performance.

  4. #4
    Quote Originally Posted by rdtompki View Post
    Thanks. I was able to find sites with that SDK available. I'm going to look more closely to see if it includes Cd data, but appears much broader in scope. The web-based model I linked to would do the trick if I overcome my laziness and enter approximate data for 9mm RN and TC bullets, for example. Does not appear the physical characteristics allowed cover defensive rounds well, but even an RN bullet might provide a good sense of short range subsonic versus longer range supersonic terminal performance.
    Have you looked at the Pesja exterior ballistics equations?

    You can find them here in an .xls format--

    http://www.jacksonrifles.com/ballistics.htm
    ''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.

  5. #5
    Site Supporter rdtompki's Avatar
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    Short term I found the very useful report, below. It's specific to 9mm at muzzle versus 100 yards. At 100 Yards you may be better off with a good 147gr subsonic round. Supers have more energy at the muzzle and are design to expand at higher velocities. Crossover is no doubt someplace in between. I'll try to back into the Cd for two representatives, but that won't address the velocity below which the supers don't offer good expansion.

    https://www.luckygunner.com/lounge/h...-at-100-yards/

  6. #6
    Quote Originally Posted by rdtompki View Post
    Short term I found the very useful report, below. It's specific to 9mm at muzzle versus 100 yards. At 100 Yards you may be better off with a good 147gr subsonic round. Supers have more energy at the muzzle and are design to expand at higher velocities. Crossover is no doubt someplace in between. I'll try to back into the Cd for two representatives, but that won't address the velocity below which the supers don't offer good expansion.

    https://www.luckygunner.com/lounge/h...-at-100-yards/
    Just an FYI, but it is probably a good idea to take any testing done with the Clear Ballistic gel product with a very large grain of salt.

    Elsewhere in this forum, while cataloging the numerous problems with the Clear Ballistic gel product, I wrote:

    "Counting the 3-part series by PoliceOne, those who've been able to discount both claims made by Clear Ballistics Gel, LLC that their product 1.) shear response-validates correctly and 2.) accurately represents the terminal ballistic behavior (specifically, post impact expansion and maximum penetration depth) of projectiles now consists of three independent sources:

    1.) PoliceOne/Mike Wood: https://www.policeone.com/police-pro...kEYB93TAd5o6J/

    2.) Brassfetcher/John Ervin: https://www.youtube.com/watch?v=5pqPBnSYTIc

    3.) TheChoppingBlock/Andrew Butts: https://www.youtube.com/watch?v=xJF-...ature=emb_logo

    Then, 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) produced by ShootingTheBull410—

    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—

    Attachment 47355

    —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—

    Attachment 47356

    —which constitutes a 25% loss of maximum terminal penetration depth all due to the insufficient physical-material response of the Clear Ballistics Gel product.

    The failure of the Clear Ballistics Gel product to correctly represent the temporary and permanent cavitation produced by projectiles being tested in it is due to the fact that the rheology of the Clear Ballistics Gel product (which is composed of a tri-block copolymer plasticized by a paraffinnic processing oil) has a very much lower strain-energy storage and loss modulus than does properly prepared 10% ordnance gelatin.

    The Clear Ballistics Gel product deficiency is well-documented here:

    https://apps.dtic.mil/dtic/tr/fulltext/u2/a505788.pdf

    And here:

    https://www.arl.army.mil/arlreports/2006/ARL-RP-134.pdf

    This well-documented lack of material response properties in the Clear Ballistics Gel product results in the projectile rebound behavior seen in the video (and elsewhere in other videos) linked above.

    Furthermore, as the Clear Ballistics Gel product is recycled for re-use as is recommended by the manufacturer, the shear-response properties and the formulation of the product itself will change as volatiles in its composition are driven off during the ''remelt/recast process'' resulting in constantly changing physical-material properties of the Clear Ballistics Gel product. So, even if terminal ballistic testing is confined to any one given production lot of the Clear Ballistics Gel product, test results will also vary over the course of its use as that particular lot Clear Ballistics Gel product "evolves" during repeated recycling over its lifetime.

    Given the expense (approximately $130.00) of just one 16 in. × 6 in. × 6 in. block of the Clear Ballistics Gel product and its failure to live up to any of the manufacturer's claims that their product 1.) shear response-validates correctly, 2.) accurately represents the terminal ballistic expansion and penetration of a projectile passing through it, and 3.) its ability to be recycled without altering its physical-mechanical properties, there seems to be no real advantage to relying upon the Clear Ballistics Gel product for such testing unless one is merely interested in "shooting stuff just for shits and grins".

    The more closely the Clear Ballistics product is examined, the more issues come to light and all of it suggests that the product is a failure. I suspect that, so long as people are willing to buy the Clear Ballistics Gel product without questioning its technical relevance and accuracy, they'll keep selling it and the 'net will continue to be swamped with waves of this sort of testing. Even now, one need only look as far as one major online ammunition retailer who has invested heavily in published testing using the Clear Ballistics Gel product as an advertising program, to see that people are now relying upon dubious data obtained in the Clear Ballistics Gelatin product to decide what they will load and carry in their defense sidearms.

    What really concerns me is that if a manufacturer was marketing a projectile design for self-defense that failed to perform as advertised those testing it and observing the failure would be holding the manufacturer responsible for such a misrepresentation. Yet, no such response exists in the testing community when it comes to the Clear Ballistics Gel product.''
    These issues become so evident that most folks who start out using the CBG product, eventually find themselves using 10% ordnance gelatin for its higher validity and, in the process, discovering that 10% ordnance gelatin is really no more expensive to use than the inferior CBG product.
    ''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.

  7. #7
    Site Supporter rdtompki's Avatar
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    I was more interested in the velocity at range. That data suggests little difference in energy at that range. Of course the hold-over for the slower bullet needs to be taken into account. Long term when 300BLK ammo becomes what I consider affordable/reasonable I'll buy an upper for truck gun duty.

  8. #8
    Quote Originally Posted by rdtompki View Post
    I was more interested in the velocity at range.
    Got it.

    Quote Originally Posted by rdtompki View Post
    I was more interested in the velocity at range. That data suggests little difference in energy at that range. Of course the hold-over for the slower bullet needs to be taken into account. Long term when 300BLK ammo becomes what I consider affordable/reasonable I'll buy an upper for truck gun duty.
    Another option—once you've obtained what you believe to be a reasonable CD that works across sonic/tran-sonic regimes—is this website:

    http://www.jbmballistics.com/ballist...culators.shtml

    They have simplified and modified point mass trajectory programs, all with drag functions (G1, G2, G5, G7, G8, GI, and GL). The modified point mass calculator might be of interest to you since offers the ability to input the dimensional values you want.

    http://www.jbmballistics.com/cgi-bin/jbmmpm-5.1.cgi
    ''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.

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