Welcome back to "Smarter Every Day."

As long as I've understood the physics,

I've wanted to visualize the Shock Wave

on the front of a super sonic bullet.

But the problem with doing this,

is you have to have access

to some pretty expensive optical hardware.

Which is why I'm pretty excited

about this giant 16" parabolic mirror.

Which is going to let us play around

with the speed of sound.

Let's go get "Smarter Every Day".

Okay, We're going to use a Schlieren Setup

to get these bullet images.

Here's how it works.

So we have the camera right here, right.

So this is a Phantom v2511.

We have a mirror way over there and the way we're doing that

is that we have a point source here.

So we're shining that light and it's spreading out;

and as it spreads out it hits this mirror,

and it bounces back and as it bounces back,

it comes down to a point.

One point right there

and we're cutting off half of that light.

Long story short it comes right here

flips back over goes into the lens.

If the air is less dense then light travels

through it faster.

If air is more dense light travels through it slower,

that causes the light to move or bend,

as it goes through different types of air;

and then we can detect those shadows

using this Schlieren Setup.

This is my buddy Coop.

He's gonna shoot through his own shop.

We're not gonna do this, you know

(cow mooing)

- I'm not shooting at his shop.

I think we're ready.

- On target.

- Three, Two, One.

Fire. (gunshot)

Whoo huhu

(gun clicks) - Weapon Clear.

- That's a big boom.

So let's see if we got it.

(laughing)

- [Male] Come here Coop

- [Destin] Oh Coop, come look at this.

(sound wave)

- [Male] Oh Cool

- [Destin] That's unbelievable.

Okay, so I'm gonna save that.

I like to guess where the shock waves come from.

The initial one looks like its coming off the bullet itself.

But then later there seems to be this weak one

that I'm guessing that reflected from the plywood table

that the mirror is sitting on.

Not really sure about that.

But then there's this stronger one that comes after that

and my guess for that one

is that it's coming off the concrete floor,

because it's more of a pure reflection.

Then later if you fast forward the video

you can see there's a very week shock wave coming across,

and my guess is that's coming from the muzzle itself.

I'm not sure on all these.

I canna have to extrapolate,

but that's kinda part of the fun.

Three, Two, One.

Fire. (gunshot)

(laughing)

(sound waves)

That's legit man.

Okay so we've dropped it to 28 thousand frames per second.

We're trying to get a really good single image.

Fire. (gunshot)

(coughing)

I actually put air in my lungs.

(sound waves)

This footage looks amazing.

But to understand exactly what we're looking at

why don't we build a little bitty model

with a bullet and a stick and talk about it here.

So lets imagine that we've got this bullet sitting here

and we've got circles emitting from the front.

As we move this thing watch what happens.

Those circles will stack up in the front

and they kind of relax in the back and they expand, right.

So that's a normal flight.

What happens if the velocity at which we move thing,

out runs those circles moving away?

Check this out.

As we start to out run it,

you'll notice that we this expansion in the back here

and it tapers down and we get this angle.

We get this, I don't know what you'd want to call it, right.

We've got a cone here.

What happens if we move forward even faster?

(whooshu)

That angle that we made there is even shallower or pointier.

That's called the Mach Angle

and people use that to measure the exact velocity

of a bullet traveling through air.

There's a simple equation.

The Mach number is equal to one over sine of that angle

and you can figure out how fast it's moving.

I use the circle illustration

because that's the way I was taught in my Aerodynamic book.

But if you look at the high speed imagery,

you can actually see circles

being formed at regular intervals.

I don't understand what they are, but they clearly there.

What we're about to do is what I've wanted to do

from the day I understood what Schlieren Imagery was.

We're going to shoot a Subsonic and a Supersonic round,

and we're going to compare the difference in the shock wave.

Coop, whatta we have?

- [Coop] So this is a 300 blackout.

- [Destin] If I understand correctly.

The whole point of this particular round

is to keep it Subsonic.

- Correct.

[Destin] This is a heavier bullet.

- This is a by 100 grains.

Almost twice the weight of this bullet here,

and so this bullet right here

you'll get somewhere around 1080 feet per second

at the muzzle.

Whereas this bullet right here

will give you somewhere in the neighborhood of 1500.

[Destin] Do you know what the sound of speed is?

- Yeah, it's like 12 something.

[Destin] I don't know.

We'll put it on the screen, right here.

That's the speed of sound.

So this one above the sound, that one's below.

All this is on purpose because that weapon

and that cartridge design was made specifically

because of these physics.

- So lets do Supersonic first.

- [Coop] Sure.

- Okay.

Three, Two, One.

Fire. (gunshot)

(sound waves)

This shock wave looks very similar to the 50 cal

with one major difference.

The angle is more Obtuse which indicates that the bullet

is traveling much slower.

So he's chambering a Subsonic round now

and so on the Schlieren we should see

a drastically different image.

Two, One.

(gunshot)

(sound waves)

It looks like, it looks like(laughing)

- [Coop] (laughing) I can make it, I can make it.

(sound waves)

- [Destin] Alright, so this is a Subsonic bullet.

So why I we seeing these little flickery things

on the side of the bullet?

That doesn't make a lot of sense to me.

So this what I always do in a situation like this.

I went looking for expert, which lead me to Dr. Kanistras.

A well respected aerodynamics professor

at University of Alabama in Huntsville.

One thing we saw on the Subsonic bullet

is we see, we didn't see that shock wave

but we saw these weird lines

out to the side of the bullet, you know.

- [Dr. Kanistras] What is the speed, when you say Subsonic?

- [Destin] It's about 10 percent less

than the speed of sound.

- You have Supersonic flow there.

It's a Normal Shock.

What you see there.

- [Destin] On a Subsonic bullet?

- Uh-huh, what is happening on a commercial aircraft?

It goes between point eight to one point two.

Even if you're flying Subsonic,

you have acceleration of the flow.

So you're reaching one point two.

- [Destin] What?

- Then you going back Subsonic.

- [Destin] So what you're saying is even though I have,

- [Dr. Kanistras] It's a Normal Shock.

- [Destin] I have a Subsonic bullet

but the speed of the air is Supersonic right there,

half way up the bullet.

So on this Subsonic bullet, those things I'm seeing,

you're saying that's Supersonic flow.

- That's right.

- [Destin] And it's because the air

has to move out of the way around the bullet.

So it has to accelerate.

- That's right, yeah

- [Destin] Really.

- So the flow accelerates, and creates a Normal Shock there.

- [Destin] It's because this particular bullet

is so close to the speed of sound.

- It reaches a transsonic speed,

which is point eight to one point two.

So even if it's not supersonic at this point,

at some point on the surface it will become Supersonic.

- [Destin] That's cool.

Thank you.

(laughs)

That's really cool.

Thank you for explaining that.

After this we decided to move closer to the mirror,

so we could see what the muzzle blast

(gunshot)

from the weapon itself look like.

(sound waves)

After that we moved the muzzle back about a foot

so we could see that transition period

(gunshot)

where that bullet pierces through the blast itself.

What's even more impressive

is each one of those tiny grains of propellant

had that visible shock wave

you could see associated with it.

(sound waves)

One more thing real quick, we took video of revolver.

It literally leaks shock waves out of the side.

But before I show you that

I want to say thank to the sponsor which is Audible.

Audible has been a partner for "Smarter Every Day" forever,

and I'm very grateful because I enjoy getting smarter

by listening to books as I drive.

This is like the perfect Brand match for me.

It helps me get smarter everyday.

You can get free book by going to audible.com/smarter

or text in the word "smarter" to 500 500.

I've a special book to recommend today.

It's called "THEM, Why we hate each other and how to heal,"

and it's by Senator Ben Sasse.

I steer really far away from politics at all times,

but this is not a political book.

It's about the things that are eroding away at our culture.

Things like loneliness

and the importance of your family support structure,

and how we need a scape goat;

and sometimes we get angry at other people.

when the problem is things that we are doing in own life.

It's a really good book.

So I highly recommend it.

I'm not quite done with it, but up to this point

it seems to be apolitical.

So check that out.

"THEM, why we hate each other and how to heal."

You ca get that by going to audible.com/smarter

or texting the word "smarter" to 500 500.

It's about how we can improve ourselves

by working on our communities around us.

I really like it,

and now definitive scientific proof