The Moment A Bullet Turns Into A Flashlight, Caught On Film

[The Slo Mo Guys] caught something fascinating while filming some firearms at 82,000 frames per second: a visible emission of light immediately preceding a bullet impact. The moment it occurs is pictured above, but if you’d like to jump directly to the point in the video where this occurs, it all starts at [8:18].

The ability to capture ultra-slow motion allows us to see things that would otherwise happen far too quickly to perceive, and there are quite a few visual spectacles in the whole video. We’ll talk a bit about what is involved, and what could be happening.

Spotting something unusual on video replay is what exteme slo-mo filming is all about.

First of all, the clear blocks being shot are ballistic gel. These dense blocks are tough, elastic, and a common sight in firearms testing because they reliably and consistently measure things like bullet deformation, fragmentation, and impact. It’s possible to make homemade ballistic gel with sufficient quantities of gelatin and water, but the clear ones like you see here are oil-based, visually clear, and more stable (they do not shrink due to evaporation).

We’ve seen the diesel effect occur in ballistic gelatin, which is most likely the result of the bullet impact vaporizing small amounts of the (oil-based) gel when the channel forms, and that vaporized material ignites due to a sudden increase in pressure as it contracts.

In the video linked above (and embedded below), there is probably a bit more in the mix. The rifles being tested are large-bore rifles, firing big cartridges with a large amount of gunpowder igniting behind each bullet. The burning powder causes a rapid expansion of hot, pressurized gasses that push the bullet down the barrel at tremendous speed. As the bullet exits, so does a jet of hot gasses. Sometimes, the last bits of burning powder are visible as a brief muzzle flash that accompanies the bullet leaving the barrel.

A large projectile traveling at supersonic velocities results in a large channel and expansion when it hits ballistic gel, but when fired at close range there are hot gasses from the muzzle and any remaining burning gunpowder in the mix, as well. All of which help generate the kind of visual spectacles we see here.

We suspect that the single frame of a flashlight-like emission of light as the flat-nosed bullet strikes the face of the gel is also the result of the diesel effect, but it’s an absolutely remarkable visual and a fascinating thing to capture on film. You can watch the whole thing just below the page break.

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Trebuchet Sends Eggs Flying

Without any sort of restrictions on designs for trebuchets, these medieval siege weapons are known to send 90 kilogram projectiles over 300 meters. The egg-launching trebuchet contest that [AndysMachines] is entering, on the other hand, has a few limitations that dramatically decreased the size of the machines involved. The weight of the entire device is limited to no more than 3 kg, with any physical dimension no more than 300 mm, but that’s more than enough to send an egg flying across a yard with the proper design and tuning for maximum distance.

Trebuchets distinguish themselves amongst other siege weapons by using a falling weight to launch the projectile. The rules of this contest allow for the use of springs, so [AndysMachines] is adding a spring in between the trebuchet arm and the weight in order to more efficiently deliver the energy from the falling weight. More fine tuning of the trebuchet was needed before the competition, though, specifically regarding the stall point for the trebuchet. This is the point where the forces acting on the arm from the projectile and the weight are balanced, and moving this point to allow the projectile to release at a 45-degree angle was needed for maximum distance.

The video goes into a lot of detail about other fine-tuning of a trebuchet like this, aided by some slow-motion video analysis. In the end, [AndysMachines] was able to launch the egg over ten meters with this design. Of course, if you want to throw out the rule book and replace the eggs with ball bearings and the aluminum and steel with titanium, it’s possible to build a trebuchet that breaks the sound barrier.

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THOR Microwaves Drone Swarms

In recent years small drones have gone from being toys and photography tools to a deadly threat on the battlefield. Kamikaze drones have become especially prominent in the news due to their use in the war in Ukraine by both sides. While we haven’t seen coordinated swarms being actively employed on the modern battlefield, it’s likely only a matter of time, making drone swarm defense an active field of development in the industry.

The US Air Force Research Laboratory recently conducted tests and a demonstration of an anti-drone weapon that uses pulses of high-power microwave energy to fry the electronics of a swarm of drones. Named the Tactical High-power Operational Responder, or THOR  (presumably they picked the acronym first), it’s housed in a 20ft shipping container with large microwave antenna on top. The form factor is important because a weapon is only useful if it can reach the battlefield, and this can fit in the back of a C130.

THOR likely functions similarly to a shotgun, with a relatively large effective “beam.” This would have added advantages like frying multiple drones with one pulse and not needing pinpoint tracking and aiming tech required for projectile and laser-based weapons. Depending on its range and directivity, THOR might come with the downside of collateral damage to electronics close to its line of fire.

Drone swarms are of course the other side of this arms race, but fortunately they also have non-destructive uses like lights shows and perhaps even 3D printing.

Cheap Camera Gives Clay-Pigeon’s-Eye View Of Trap Shooting

Speaking from experience, it’s always fun to build something with the specific intention of destroying it. Childhood sessions spending hours building boats from scrap wood only to take them to a nearby creek to bombard them with rocks — we disrespectfully called this game “Pearl Harbor” — confirms this. As does the slightly more grown-up pursuit of building this one-time-use clay pigeon camera.

The backstory on this build, which dates all the way back to 2017, is that [Thomas] was invited to a birthday bash at the local shooting range for a round of trap shooting. For the uninitiated, trap is a sport that involves launching a clay disc (known as a pigeon) into the air as a moving target and shooting it down with a shotgun. It’s a lot of fun, but [Thomas] was looking for a way to make it even more fun.

After toying with the idea of buying a cheap drone for aerial target practice, he settled on the idea of making a clay pigeon camera. After procuring a cheap keychain camera, he designed a simple wind vane mount for the camera, to keep it pointed in one direction rather than spinning with the pigeon. The wind vane was 3D printed and attached to the pigeon with a skate bearing, and the rig was ready for the range. The snuff film below tells the whole tale; the camera performed admirably and the wind vane did a good job of steadying the camera for all of about five seconds, until the inevitable and dramatic demise of the pigeon.

Watching this makes us feel like we need more projects designed for intentional destruction. Safety first, of course, but we’d be keen to see what everyone comes up with.

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Tiny Palm-Sized Crossbow Build Is Cute And Dangerous

Crossbows were a major development in the history of weaponry. They enabled lesser-skilled soldiers to shoot arrows at great speed in a compact form-factor. You can now build your own tiny version, thanks to this creation from [Maciej Nowak].

The main body of the crossbow was cut from a piece of aluminium bar stock, being shaped with an angle grinder. A slot was then machined to mount the crossbar and pulleys. A round piece of aluminium tube serves as a spring holder, and the spring is tensioned via pulling back a length of sailing rope to rest on a latch. The latch is released by a small trigger, just like on a full-size crossbow.

The arrows (or bolts, more typically) were made by machining skewers and giving them hard metal tips cut from nails. This enables them to penetrate apples, and presumably other fruits. They fly straight enough to reliably hit a target from a meter or two away.

We’ve seen other crossbow builds before, like this one that fires cannonballs! Just be careful where you aim, and don’t get yourself or anyone else hurt.

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A circular wheeled robot sits on a white background. There is a green tank of butane/propane in the center surrounded by wires and electronics.

Doomba: Purifying Your Floors With Fire

If you’ve ever thought that your floor cleaning robot eating the fringe on your rug wasn’t destructive enough, [Kyle Brinkerhoff] is working on a solution — Doomba.

This blazingly fast RC vehicle has a tank of butane/propane gas nestled snugly amid its electronics and drive system to fuel a (not yet implemented) flamethrower. Watching how quickly this little bot can move in the video below certainly made our hearts race with anticipation for the inevitable fireworks glory of completed build. Dual motors and a tank-style drive ensure that this firebug will be able to maneuver around any obstacle.

As of writing, the flamethrower and an updated carriage for the drivetrain are underway. Apparently, spinning very quickly in circles can be just as disorienting for robots as it is for us biological beings. During the test shown below, the robot kicked out one of its drive motors. [Kyle] says the final touch will be putting the whole assembly inside an actual Roomba shell for that authentic look.

With spooky season upon us, it’s always good to have the cleansing power of fire at hand in case you find more than you bargained for with your Ghost-Hunting PKE Meter. While there’s no indication whether Doomba can actually run DOOM, you might be interested in this other Doomba Project that uses Roomba’s maps of your house to generate levels for the iconic shooter.

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Six Shooter Swaps Powder For Popped Capacitors

Modern firearms might seem far removed from the revolvers of the Old West, but conceptually, they still operate on the same principle: exploding gunpowder. But as anyone who has put too much voltage through an electrolytic capacitor knows, gunpowder isn’t the only thing that explodes. (Yes, it isn’t technically an explosion.)

[Jay Bowles] wondered if it would be possible to construct an electrically-fired weapon that used used a standard capacitor in place of the primer and powder of a traditional cartridge. While it would naturally have only the fraction of the muzzle velocity or energy of even the smallest caliber firearm, it would be an interesting look at an alternate approach to what has been considered a largely solved problem since the mid-1800s.

In his latest Plasma Channel video, [Jay] walks viewers through the creation of his unconventional pistol, starting with a scientific determination of how much energy you can get out of popped capacitor. His test setup involved placing a capacitor and small projectile into an acrylic tube, and noting the relation between the speed of the projectile and the voltage passed through the cap. At 30 VDC the projectile would reliably fire from the barrel of his makeshift cannon, but by tripling the voltage to 90 VDC, he noted that the muzzle velocity saw the same 3X improvement.

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