Estimating Rate of Bullet Deformation from Ballistic-Gel Cavity Profile

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Flintstone
Posts: 17
Joined: Wed Mar 29, 2017 12:08 am UTC

Estimating Rate of Bullet Deformation from Ballistic-Gel Cavity Profile

Postby Flintstone » Wed Apr 19, 2017 8:05 am UTC

Hi. I've been trying to program a ballistic wounding simulator for a game, and I've made some good progress modeling the body and the damage of bullets. A problem I've encountered, is to properly simulate hollow-point injuries in the game I'd need to know the curving rate of a bullet's deformation.

The problem is, this information is not freely available anywhere I can find, so the only way to get this data seems to be to reverse engineer it from test results.

This image is an example of data which can be used to reverse engineer the deformation rate of the bullet. It shows the permanent cavity caused by .308 rounds in ballistic gel: http://www.rathcoombe.net/sci-tech/ball ... plot_3.jpg

This site is where the image is from, and has more details about the test data: http://www.rathcoombe.net/sci-tech/ball ... thods.html

They have provided data for each of the rounds tested in the above image:


Image:
Spoiler:
Image

Code: Select all


Bullet Type / Mass         Impact Velocity      Expanded Diameter   Depth of Penetration      Retained Weight

250 gr Barnes Original         2340 fps         0.685 in            11.5 in            165 gr / 66 %
220 gr Woodleigh Weldcore RN      2328 fps         0.702 in            11.7 in            199 gr / 91 %
220 gr Winchester Silvertip      2410 fps         0.638 in            10.9 in            158 gr / 72 %
220 gr Nosler Partition         2470 fps         0.460 in            20.5 in            153 gr / 70 %
220 gr Hornady Interlock RN      2370 fps         0.514 in            13.9 in            121 gr / 55 %

I apologize for the uneven chart. The code tags are not responding the same way my TXT file does.


I believe there is enough data here to reverse engineer the rate of penetration. The issue is that I don't know what formulas to use to get the information. There is a selection of different variables that come into play here, and it does not seem easy to work out the answer.


Energy: The bullet loses energy as it travels through the media (in this case, ballistic gel). However, the more expanded the bullet is, the more resistance it will face and the faster it will lose energy.

Example: http://throwinglead.com/images/tb_45ACPFMJ.jpg
Note how the temporary stretch cavity gets less and less, as the bullet loses energy. The permanent cavity also narrows slightly, but I don't need data on that feature (to save you time). The less energy the bullet has, the less effective bullet deformation will be at creating large cavities.

Diameter: The diameter of the bullet effects the size of the wound channel it creates. Example: http://throwinglead.com/images/tb_45ACPFMJ.jpg
The size of the permanent wound path is similar to the diameter of the bullet. If the bullet is expanded, it will have a wider diameter and a wider wound channel.

Deformation: Now here's the trickiest part. Different bullets expand at different times, in different ways, at different speeds, producing dramatically different curves. When a bullet deforms, a massive amount of energy is put into the ballistic gel and it can form huge cavities--if the bullet still has a lot of energy. Handgun rounds don't have enough energy to produce large permanent cavities, so we're mainly looking at .308 rifle rounds.


Is there any way to estimate the curve of deformation for such bullets, without tens of hours of work? If this problem is too difficult for the skilled mathematicians and enthusiasts here, I expect I am completely out of luck for finding out the rate of deformation for these bullets, in my game.

Thank you for reading and taking interest, and for any advice you can give me.

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