How Ammo Temperature Will Affect Shooting Accuracy

The last time we visited the Hackaday shooting range we were all psyched up to get the right posture, breathe correctly, lower our heart rates and squeeze the trigger at exactly the right moment that the wandering cross hairs align with the target ……. and lastly accommodate the inevitable recoil. But never did we think to check the temperature of our ammo! Ok, temperatures aren’t likely to vary that much there unless the range cat chooses to lay down on top of the ammo box, but out in the wilderness the temperatures can easily vary by up to 30 degrees, which would certainly be a problem.

If we take a quick look at what’s happening on Johnny’s Reloading Bench  we get an in depth comparison of different powders at different temperatures, with data being collected via a bullet velocity radar. If nothing else, it’s interesting just to get a peep into the mysterious world of ‘Reloading’ where every one of the tiny kernels or ‘balls’ of powder make a difference and different powders require particular primers to make them burn properly.

Just to make it clear, bullet speed makes a big difference to the trajectory, especially at long distances. For example, if the bullet were to travel at close to the speed of light, there would be almost no trajectory at all and the shooter would not have to adjust the vertical aim for distance. Normally, we have to aim upwards to hit the target:

It may be that we ‘zero in’ our sights at room temperature, but then end up actually shooting the firearm on a cold, frosty morning with cold ammo, and given what we have now learnt from the video, we could now make a small adjustment for that eventuality, depending on the particular ammo we are using. Johnny’s video is after the break:

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Making A Bronze Cannon From Scratch

Casting metal at home is somewhat tricky, but there’s no denying the results can be quite rewarding. [FarmCraft101] put his incredible craftsmanship on display, and learned a few new things in the process, by scratch building a scale replica bronze cannon and carriage.

Starting with a sufficient quantity of scrap metal, he first produced bronze ingots. Getting the actual casting right took multiples attempts. First tried a lost foam cast, which failed miserably, but provided a sample metal which was put through tensile strength testing. The second attempt was done using a wood barrel form and a split mold, and was cast horizontally which resulted in shrinkage on top of the barrel. The third attempt, arranged vertically, almost resulted in a high risk game of “the floor is lava”, with molten bronze pouring out across his garage floor after the mold split open during casting.

Attempt number four was finally successful, again using a vertical mold but with more sturdy clamping. This roughcast barrel was then drilled out and finished to a beautiful mirror with the help of a lathe and a lot of elbow grease. He then turned his attention to the carriage, which itself is a real beauty featuring custom wagon wheels with a charred wood finish and linseed oil coating.

You can check out the build video after the break, but we’ll warn you now, [FarmCraft101] never actually fires this gorgeous creation. If you’d like to try your hand at DIY cannoneering and have a 3D printer, you might want to give lost PLA casting a try, or go into mass production with some DIY silicone molds.

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3D Printing Is Transformative Experience For Airgun Shooter

It’s interesting to peek into other scenes and niches and see how they intersect with things that one may find commonplace, like 3D printing. In this case, [NewToOldGuns] wrote a guest blog post for PyramydAir (a retailer, so be prepared for a lot of product links) about how 3D printing has completely transformed the experience of how he uses one of his favorite airguns, and allowed him to make changes and improvements that would not otherwise have been practical.

Not only are the 3D printed improvements thoughtful and useful, but it’s interesting to see familiar insights into the whole design process. After explaining some 3D printing basics, he points out that rapid iteration is key to effective prototyping, and a 3D printer can allow that to happen in a way not previously possible.

The pellets held inside the silver cylinder can no longer fall out, and the orange holder allows it to be simply pushed straight through into the gun’s receiver.

It all started with the small magazine which holds the rifle’s projectiles. It would be really handy to pre-load these for easier reloading, but there were practical problems preventing this. For one thing, there’s nothing to really hold the pellets in place and keep them from just falling out when it’s not loaded into the gun. Also, loading them into the gun without letting anything fall out was awkward at best. The solution was to design a simple holder that would cradle the magazine and cover the front and back to keep everything in place. [NewToOldGuns] also designed it so that it could mate directly to the gun, so the magazine could simply be pushed straight into the receiver while the action was held open.

Once this simple part was working, the floodgates of creativity were opened. Next was a belt attachment to hold multiple reloads, followed by a decision to mount the reloads directly onto the gun instead. An improved lever and sights quickly followed.

I also demonstrated the iterative approach to prototyping when I designed a simple alarm to detect when my 3D printer’s filament had run out. [NewToOldGuns] observes that the real power of 3D printing isn’t being able to make bottle openers or coat hooks on demand. It’s the ability to imagine a solution, then have that solution in hand in record time.

British Cops Catch Shooter-Printing Villain

It’s a perennial of breathless British tabloid scare reporting that 3D printers will unleash a tide of weapons upon the streets. But perhaps it might actually be time for Brits lock up their children, because London’s Metropolitan Police have announced their first prosecution for 3D printing a handgun. The gun pictured appears to be a Repringer 5-shot .22 revolver, and was found by police during a drugs raid.

The UK has significantly restrictive firearms legislation and shooting incidents are extremely rare in the country, so while this might not raise any eyebrows on the other side of the Atlantic it’s an extremely unusual event for British police. It appears that the builder was not the type of libre firearms enthusiast who has made the news with similar work in the USA, so it has to be assumed that it was printed purely as a means to secure an illegal firearm however rough-and-ready or indeed dangerous it might be.

Stepping aside from the firearm aspect of the story, it should be of concern for any British 3D printer enthusiasts. As we’ve reported over the years with respect to drone incidents they can sometimes throw reason to the wind when faced with unfamiliar technology, indeed we’ve already seen them imagining RepRap parts to be for a firearm. We’d counsel all parties to keep sane heads, and hope that both the sentence for today’s criminal proves to be a suitable deterrent, and that no clueless fool decides to download and print another weapon for the hell of it. As always, we’ll bring you developments as they happen.

3D Printed Spuds Are Begging To Be Fired

The ballistics of humble potato is a time-honoured research topic for everyone who likes things that go bang. The focus of such work is usually on the launcher itself, with the projectiles being little more than an afterthought. [drenehtsral] decided that the wares of the local organic ammunition supplier were not good enough for him and his minions, so he designed and then 3D printed some rifled potato cannon slugs.

The design was done using OpenSCAD, has a number of adjustable parameters like infill and rifling. We doubt that the rifling introduces any spin, since it is being fired from a smooth bore barrel, but as always 3D printing brings the capability to quickly test different ideas. A quick search on Thingiverse shows a number of 3D printed spuds, so [drenehtsral] is not the first give it a go. However, this did bring to our attention that the field of spud gun projectiles is begging to be explored.

There is enough space inside a projectile to fit an IMU and logging electronics, which would give some very nice empirical data (providing you can recover it of course) on spin, acceleration, and trajectory that can be used to further improve designs. Spring loaded stabilising fins would be cool, and maybe someone can even manage to implement some form of guidance? The possibilities are endless! If you’re up for the challenge, please document your work it and let us know.

As you would expect we have no shortage of potato cannon themed content, ranging from cartridge firing and bolt action versions to antenna launchers and Arduino-powered fire control systems.

Eagle Reborn: F-15 Simulator From A Wreck

This story started all the way back in September 12, 1981, when an F-15C aircraft’s landing attempt at Soesterberg Airbase during an airshow went completely FUBAR and the airframe was scrapped. The forward fuselage section was sold and eventually ended up with [Gene Buckle] who began work on creating a fully accurate F-15C simulator using these parts. He has blogged about his progress since 2009 over at the project website.

The F-15C was number 80-0007, which at the time of the crash had flown only 9.5 hours total, making it a very early retirement for an incredible fighter jet. But now the Eagle is back, or at least part of it: [Gene] managed to get the whole system into a state where the instrumentation and controls work again, using the original computer systems and instruments where they were still usable. You can find the YouTube video embedded after the break as well.

Detailed technical information on the F-15 series and this simulator build can be found on the project site, which is awesome both for F-15 fans and those who are into really accurate simulators.

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3D Printing May Be The Key To Practical Scramjets

The first scramjet, an airbreathing jet engine capable of pushing an aircraft beyond Mach 5, was successfully flown in the early 1990s. But while pretty much any other technology you could imagine has progressed by leaps and bounds in the nearly 30 years that have passed, the state-of-the-art in hypersonic scramjets hasn’t moved much. We still don’t have practical hypersonic aircraft, military or otherwise, and any missiles that travel at those sort of speeds are rocket powered.

NASA’s X-43 hit Mach 9.6 in 2004

This is somewhat surprising since, at least on paper, the operating principle of the scramjet is simplicity itself. Air rushing into the engine is compressed by the geometry of the inlet, fuel is added, the mixture is ignited, and the resulting flow of expanded gases leaves the engine faster than it entered. There aren’t even any moving parts inside of a scramjet, it’s little more than a carefully shaped tube with fuel injectors and ignitors in it.

Unfortunately, pulling it off in practice is quite a bit harder. Part of the problem is that a scramjet doesn’t actually start working until the air entering the engine’s inlet is moving at around Mach 4, which makes testing them difficult and expensive. It’s possible to do it in a specially designed wind tunnel, but practically speaking, it ends up being easier to mount the engine to the front of a conventional rocket and get it up to speed that way. The downside is that such flights are one-way tickets, and end with the test article crashing into the ocean once it runs out of fuel.

But the bigger problem is that the core concept is deceptively simple. It’s easy to say you’ll just squirt some jet fuel into the stream of compressed air and light it up, but when that air is moving at thousands of miles per hour, keeping it burning is no small feat. Because of this, the operation of a scramjet has often been likened to trying to light a match in a hurricane; the challenge isn’t in the task, but in the environment you’re trying to perform it in.

Now, both Aerojet Rocketdyne and Northrop Grumman think they may have found the solution: additive manufacturing. By 3D printing their scramjet engines, they can not only iterate through design revisions faster, but produce them far cheaper than they’ve been able to in the past. Even more importantly, it enables complex internal engine geometries that would have been more difficult to produce via traditional manufacturing.

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