Explosion inside ballistics gel??

BigBore44 · Dec 18, 2017

I was perusing youtube last night looking for new videos of people with guns and stumbled upon this video.

Of course the video teaser pic has girls on it as most videos on YouTube do. But at the 30 second mark or so it shows a S&W (44 mag most likely) discharging. Then shows a bullet going into and through homemade “ballistics” gel. As the bullet exits the gel, the cavity in the gel collapses. But when the gel fully collapses, there appears to be a secondary explosion inside the gel and then smoke exiting rearward (from where the bullet entered). I’ve NEVER seen this before.

Anybody have any idea what could cause this? I watched this portion of the video several times. I’m no chemist but I’m very intrigued. I wouldn’t think gel wouldn’t have enough elasticity and density to create enough compression to cause a detonation. And what gasses left from the bullet traveling through the gel could cause that? Of course I don’t know what the gel was made of. But I wouldn’t think the gel would have a flammable composition.

What do you guys/gals think?

Double Naught Spy · Dec 18, 2017

The explosion is the collapse of the cavitation bubble created by the bullet going into the gel. This happens very fast and if you were there next to the gel, you would hear a pop or snap sound as it occurs. When the bubble collapses, it generates heat, purportedly 8000 degrees or so, hotter than the sun, but only for a split second which is an implosion. This is all called sonoluminescence.

edwardware · Dec 18, 2017

Double Naught Spy said:
This is all called sonoluminescence.

Nope, sorry, it's not sonoluminescence.

If you read up on sonoluminescence (even the Wikipedia article will do) you'll find that the energy level necessary is a couple orders of magnitude greater than you could expect in gel behind a bullet at conventional velocity. Further, the most energetic sonoluminescence created to date is barely visible to the human eye.

What you observe is a much more mundane phenomena: dieseling. The vacuum created in the expanding cavity causes some of the gel to vaporize. The compression of the collapsing cavity causes adiabatic heating of the vapor past its flash point, and it combusts. This is essentially the same process as adiabatic combustion in a diesel engine.

BigBore44 said:
I’ve NEVER seen this before.
. . .
But I wouldn’t think the gel would have a flammable composition.

Most high quality/high speed video of bullets over 3000ish fps will show this. The best example is Jerry Miculek's 460 Mag videos.

Ballistic gel is made of collagen. Like all organic matter, it can be oxidized, and pretty easily once it's atomized or vaporized.

BigBore44 · Dec 18, 2017

edwardware said:
Nope, sorry, it's not sonoluminescence.

If you read up on sonoluminescence (even the Wikipedia article will do) you'll find that the energy level necessary is a couple orders of magnitude greater than you could expect in gel behind a bullet at conventional velocity. Further, the most energetic sonoluminescence created to date is barely visible to the human eye.

What you observe is a much more mundane phenomena: dieseling. The vacuum created in the expanding cavity causes some of the gel to vaporize. The compression of the collapsing cavity causes adiabatic heating of the vapor past its flash point, and it combusts. This is essentially the same process as adiabatic combustion in a diesel engine.

Most high quality/high speed video of bullets over 3000ish fps will show this. The best example is Jerry Miculek's 460 Mag videos.

Ballistic gel is made of collagen. Like all organic matter, it can be oxidized, and pretty easily once it's atomized or vaporized.

Very interesting. Thanks guys.

JR24 · Dec 18, 2017

Guess I don't watch enough big bore gel tests, that's facinating!

Klint Beastwood · Dec 18, 2017

It’s called sonoilluminecence

edwardware · Dec 18, 2017

JR24 said:
Guess I don't watch enough big bore gel tests, that's facinating!

Here, at about 3 minutes, is a good example:

Here's another, at about 3:45:

Flechette · Dec 19, 2017

BigBore44 said:
I was perusing youtube last night looking for new videos of people with guns and stumbled upon this video.

Of course the video teaser pic has girls on it as most videos on YouTube do. But at the 30 second mark or so it shows a S&W (44 mag most likely) discharging. Then shows a bullet going into and through homemade “ballistics” gel. As the bullet exits the gel, the cavity in the gel collapses. But when the gel fully collapses, there appears to be a secondary explosion inside the gel and then smoke exiting rearward (from where the bullet entered). I’ve NEVER seen this before.

Anybody have any idea what could cause this? I watched this portion of the video several times. I’m no chemist but I’m very intrigued. I wouldn’t think gel wouldn’t have enough elasticity and density to create enough compression to cause a detonation. And what gasses left from the bullet traveling through the gel could cause that? Of course I don’t know what the gel was made of. But I wouldn’t think the gel would have a flammable composition.

What do you guys/gals think?

I am sure that someone must’ve asked this before, but how do people have so many full auto firearms that were clearly made after 1986?

Double Naught Spy · Dec 19, 2017

edwardware said:
Nope, sorry, it's not sonoluminescence.

If you read up on sonoluminescence (even the Wikipedia article will do) you'll find that the energy level necessary is a couple orders of magnitude greater than you could expect in gel behind a bullet at conventional velocity. Further, the most energetic sonoluminescence created to date is barely visible to the human eye.

So much energy, in fact, that it can be produced by a very tiny pistol shrimp in the ocean.

LoneGoose · Dec 19, 2017

And I noticed in the OP video that after the smoke puffs out, there is some visible black stuff (carbon?) in the cavity.

I learn new stuff every time I get on THR, which rocks.

Bill50 · Dec 19, 2017

Flechette said:
I am sure that someone must’ve asked this before, but how do people have so many full auto firearms that were clearly made after 1986?

By getting an FFL then paying whatever other special occupation taxes they need. Not an expert on which taxes they need to get paid for regular firearms vs nfa.

Most of the people you see in these types of videos are small gun store owners, their friends/family, or people they are renting to.

TeaCoffee.Guy · Dec 30, 2017

I may have to apologize for my ignorance.........
but in that video those people seem to be just blasting away without aiming or controlling the gun. (BangBangBangBangBangBang)
Wouldn't it be more fun to aim carefully and shoot one shot at a time and look to see if you have even hit the target? (Bang, Oops I missed)
Another thought that I had - I like looking at girls too, but when I am shooting a gun I try to keep my mind being accurate and safe.

JellyJar · Dec 30, 2017

Look up fire pistons on Wikipedia:

https://en.wikipedia.org/wiki/Fire_piston

It uses compressed air to light a small piece of tender to start a fire by using air compression.
Same thing as is happening in that block of gel.

Explosion inside ballistics gel??

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