Need a little help, please -- Calibrating ballistic gelatin

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    Ballistic Ballistics
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SUMMARY

This discussion focuses on calibrating ballistic gelatin for .45 ACP ammunition tests, specifically using a standard 0.177" BB shot at 590 feet per second (fps) to achieve a penetration depth of 8.5 cm. The participant's BB gun only reaches 350 fps, approximately 60% of the required velocity, raising questions about the proportionality of penetration depth. Experts confirm that while a linear correction exists for BB speeds close to the target, penetration is not directly proportional, especially when the velocity is significantly below the target. Proper calibration and preparation of the gelatin block are crucial for valid test results.

PREREQUISITES
  • Understanding of ballistic gelatin calibration standards
  • Knowledge of BB gun specifications, particularly the Crosman 2100 Classic
  • Familiarity with the physics of projectile motion and penetration dynamics
  • Experience in preparing ballistic gelatin according to specific recipes
NEXT STEPS
  • Research the calibration process for ballistic gelatin and its importance in ballistic testing
  • Learn about the Crosman 2100 Classic BB gun and its performance characteristics
  • Study the effects of velocity on penetration depth in ballistic gelatin
  • Explore best practices for preparing and storing ballistic gelatin blocks for testing
USEFUL FOR

This discussion is beneficial for ballistic researchers, firearms enthusiasts, and anyone involved in ammunition testing and calibration, particularly those interested in accurate ballistic performance assessments.

JunkfoodZombie
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Pardon my ignorance, guys, but I have what should be a relatively simple question for physics buffs. I haven't studied any real physics since HS...
Here is the situation:
I am performing some .45acp ammunition ballistic tests using a gelatin block. In order for my tests to be valid, I have to calibrate the block, which requires a standard 0.177" bb to be shot into the gel at 590 feet per second (+/- 15 fps) and penetrate 8.5 cm (+/- 1 cm). Easy enough. My issue is that my bb gun only achieves 350 fps. That is roughly 60% the desired velocity. My question is this: Is the desired penetration depth directly proportional? In other words, should I be looking for a penetration depth of 5.04 cm, or does deceleration act on the bb in a non-linear manner causing it to penetrate less than 60%?
I appreciate any time you take to answer this and thank you in advance. Have a good one, guys.
 
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JunkfoodZombie said:
Pardon my ignorance, guys, but I have what should be a relatively simple question for physics buffs. I haven't studied any real physics since HS...
Here is the situation:
I am performing some .45acp ammunition ballistic tests using a gelatin block. In order for my tests to be valid, I have to calibrate the block, which requires a standard .117" bb to be shot into the gel at 590 feet per second (+/- 15 fps) and penetrate 8.5 cm (+/- 1 cm). Easy enough. My issue is that my bb gun only achieves 350 fps. That is roughly 60% the desired velocity. My question is this: Is the desired penetration depth directly proportional? In other words, should I be looking for a penetration depth of 5.04 cm, or does deceleration act on the bb in a non-linear manner causing it to penetrate less than 60%?
I appreciate any time you take to answer this and thank you in advance. Have a good one, guys.

You mean a standard 0.177" diameter bb.

There is a linear correction available for bb speeds close but not quite within +/- 15 fps of the target velocity, but it will not be proportional, especially for a velocity over 100 fps out of spec.

We use a Crosman 2100 Classic pump bb gun (available from WalMart for under $70) with Avanti precision ground bbs. You can vary the number of pumps to hit the target velocity relatively accurately. The number of pumps depends on the ambient air pressure and is 7-8 near sea level and 10-11 at mountain elevations like Colorado (7000 ft).

A few other tips:

Follow the gelatin recipe very carefully. You need to weigh the gelatin and the water precisely or the block is unlikely to pass.

The block needs 2-4 days in the fridge before it is likely to pass. 4 days is better.

If you don't calibrate the block properly, your results are not really scientific and should not be compared with other results.

If you are LEO or military in the US (or a contractor for an agency), contact me via a Private Conversation, and we'll walk you through everything very carefully (without any charge) to make sure you get it all right.
 
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Dr. Courtney said:
You mean a standard 0.177" diameter bb.

There is a linear correction available for bb speeds close but not quite within +/- 15 fps of the target velocity, but it will not be proportional, especially for a velocity over 100 fps out of spec.

We use a Crosman 2100 Classic pump bb gun, which is available from WalMart for under $70 with Avanti precision ground bbs. You can vary the number of pumps to hit the target velocity relatively accurately. The number of pumps depends on the ambient air pressure and is 7-8 near sea level and 10-11 at mountain elevations like Colorado (7000 ft).

A few other tips:

Follow the gelatin recipe very carefully. You need to weigh the gelatin and the water precisely or the block is unlikely to pass.

The block needs 2-4 days in the fridge before it is likely to pass. 4 days is better.

If you don't calibrate the block properly, your results are not really scientific and should not be compared with other results.

If you are LEO or military in the US (or a contractor for an agency), contact me via email, and we'll walk you through everything very carefully (without any charge) to make sure you get it all right. Michael_Courtney@alum.mit.edu

Thank you. I appreciate the quick feedback. I didn't want to use the bb gun I have if I couldn't use it to accurately calibrate the gel. If I don't have gel that is to spec, I don't want to upload the results to my channel. I will wait until I can get it where I want it to be. The test is more of an experiment for fun, but I do want it to have some relevance for the sake of comparison to other tests. I have a tiny Youtube channel and thought it would be fun to do a test on a relatively new product so people can see some info on it early on. I will try and find the proper projectile spitter for the task at hand. Again, I appreciate the help and the quick reply. Have a good one.