Suppressor Schlieren Shock Waves in Slow Motion - Smarter Every Day 204

• A quick caveat before we get started here. I do not want Smarter Every Day to be observed as a channel that glorifies weaponry. I am just fascinated by fluid dynamics, ballistics, optics, mechanics, aerodynamics. All this stuff is just fascinating to me. And I am hard-pressed to find one singular thing that I can study that wraps all these physical phenomenon into the perfect Venn diagram that tickles my brain quite like firearms.

So, that's why you'll see me studying firearms so often and I hope you realize that I'm doing it as intelligently and respectfully as I can. That being said, I've made some observations in the last episode and I've learned some stuff. And I've also decided to push it a little further by studying suppressors. So, let's look at this and try to get smarter every day.

First, let's revisit what we learned in the last episode. Using a phantom camera with a clever photography technique called Schlieren, which is German for streak by the way, we observe that the supersonic bullet creates an angular shot cone and the angle of that cone can be used to determine the mach number. We also learned from Dr. Konigstrasse at UAH that a bullet travelling in the transonic regime can create supersonic flow around it because the air has to speed up and rush around the outside of the surface of the bullet.

This is a connection I didn't make at the time, but we've all seen these awesome pictures of a fighter jet with this cone of vapor behind it. This is totally why that happens. The jet is flying along in the transonic regime just like that bullet and just like the normal shockwave that occurs on the side of the subsonic bullet that's happening on the jet. And it does two things: number one, it makes this cone of vapor form on the jet, and number two, it makes me all tingly inside.

Okay, so I think we have a good understanding at this point of shockwaves created by a bullet itself. You may have heard someone talk about the crack of a bullet as it passes; that's created by this shockwave. But if you think about the bang of a gunshot, it's all those rapidly expanding gases out the front of a muzzle, right? So, it's time to hone in on that area right there and study that with super schlom, super slowmo suppressor Schlieren. There you go. It's hard to say.

In a past episode of Smarter Every Day, I asked a company to fabricate a see-through suppressor so we could see the flame front propagate through the baffles and try to understand what was going on. That was effective in showing what happens on the inside of their particular suppressor design, but what I wanna see is exactly what happens on the outside of the suppressor. After all, that's where all the noise is.

Here's my friend Coop firing his rifle chambered in 300 blackout, both suppressed and unsuppressed. I want to show you a full minute of slow motion video because I believe it does the best job of explaining the physics of what's going on. On the left, we have a suppressed weapon, and on the right, we have the same weapon unsuppressed. When they're first fired, you can see straight away that the weapon on the right seems to have a larger, dirtier blast. But after four milliseconds, there doesn't seem to be any more shockwaves; we're just venting the exhaust gases at that point.

The weapon on the left, however, is still chugging away. It's like this initial blast is bouncing around on the inside of the suppressor, and just a little bit of the gases are being leaked out with every reverberation. (gunshot echo) Watch what happens next though. On the right, the echo from the unsuppressed weapon is huge and very distinct. You can see how powerful and singular that initial blast was by how sharp the echo is when it returns.

Imagine that echo entering your ears; meanwhile, you can still see that the suppressed weapon is dissipating that acoustic energy slowly. This is like the clearest example I can show of that energy being dissipated differently. On the right, the unsuppressed version, the whole thing's over in a millisecond and a half, but on the left, the same acoustic energy is dissipated over 15 milliseconds. That is a direct comparison showing you that it almost acts like a capacitor in a circuit. It's like, slowly filtering the energy as it exits.

Anyway, that energy dissipation does not come for free. Suppressors heat up very, very quickly. All that thermal energy is captured because it doesn't dissipate away from the weapons. So, the problem with suppressors is if you fire enough rounds through 'em, they heat up very, very fast, and they can cause malfunctions and even damage to the weapon.

Now let's look at subsonic ammunition being fired from a suppressor. This is absolutely fascinating. Okay, first observation. The first thing that leaves the suppressor is unburnt powder, and look at that. There's a little baby shockwave; they're supersonic. Now whether this is gunk coming loose from previous shots, or whatever, I don't know, but it's clearly supersonic.

Second, did you see that little vortex ring poot out the end? Okay, here we go, bullet time. We know this is a subsonic round, so we're expecting normal shockwaves on the sides of the bullet, but look at that. They're not there until the bullet is several inches away from the muzzle. It is crazy to think about how complicated this flow environment is, but it's really fun.

What are these little squirrely things that come out of the suppressor? - Okay, so what you're seeing here on this blackout cartridge is you're seeing unburnt propellant leaving the muzzle before the bullet goes. And so for 300 blackout, optimally you get complete burnout around 9 1/2 to ten inches of barrel length. So, this is a 10.2 inch barrel length; so we're right on the threshold of burning all the propellant out before the bullet leaves the muzzle.

• But look, there was a supersonic piece of powder. - Yeah, there is. - You see that? - Whoa! - This is insane; we're just like, learning important stuff. Alright, well that was delightful. What did we learn, John? (laughs) - Propellant outruns bullets sometimes. You may have grains of propellant that exit the muzzle faster than the bullet, supersonically. - That's crazy, and there's a shockwave on those grains of propellant. - Exactly! - That's, uh, never would have thought that. - Neither would I.

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