Jet bullets

[Novus Collectus]

I wonder why I never heard about this idea attempted, a bullet with a simplistic jet engine.
Bear me out, it sounds more complicated than it sounds, this idea would have no moving parts.

Ok we all know about the Gyrojet rocket bullets, but with a jet engined bullet half the propellant would be from the air. Imagine a bullet with an air passage throiugh the center, but a venturi, compression zone and an expanmsion chamber out the end. The outside cylinder could be the fuel tank, the venturi would be the fuel supply mechanism (atomizer), the compression chamber would just be a chamber to compress the fuel air mixture enough to make it ignite and the expansion chamber could just be a conical shape out the back.

I figure a sabot would be used to fire the bullet to supersonic speed ouit the barrel and would also act as the plug of the fuel inlet until the bullet is fired.

Some liquid fuels have much more explosive or propelling potential than smokeless powders. For insance, I read somewhere that 60 pounds of gasoline has the same explosive potential as a thousand pounds of smokeless powder.
A jet bullet may be juist an academic excersise or just a cool experiment with no practical application, but what if it did have one like a high kinetic energy projectile that does not cause undue recoil upon the shooter, or extreme range bullets that can maintain high velocity over longer distances?

 

[The Lone Haranguer]

On the History Channel there was a segment about the Gyrojet (really more of a rocket). One problem with it was that the projectile actually took some time to get up to speed, making it less effective at close range and sometimes causing stoppages. I suspect you would have much the same problem with an actual jet.

 

[hnl.flyboy]

the only engines without any moving parts are ramjets and scramjets. both have to be going around the area of Mach 3 to keep exhaust from going out the front...i'm not too sure about bullet velocities (i'm an aviation nut, but getting into being a gun nut too hehehe), but i think normal rounds might be too slow. also, the method of getting fuel to feed would be hard to make for a tiny bullet...even for a 155 howitzer, it could be impractical. good idea, but hard to implement.

 

[Novus Collectus]

I forgot to mention the bullet would be propelled to supersonic speed out the barrel by normal means and would already be going supersonic when the jet engine part is activated.
And yes it would be a ramjet or better yet a scram jet principle. At sea level the speed of sound is about 2,200 MPH or 3,300 FPS which is what a high powered 30-06 can achieve.

Now as far as fuel feed, a simple venturi effect might be enough to suck the fuel to the center of the bullet and feed the air flow right before a compression chamber of the scramjet. But if not I have an idea using an archimedes screw forced flow type of deal to counteract the centrifigual (centripetal?) force of the spinning bullet making the liquid want to stay along the outside walls of the tank.

 

[CWL]

I figure a sabot would be used to fire the bullet to supersonic speed ouit the barrel and would also act as the plug of the fuel inlet until the bullet is fired.

Herein lies your problem. If you have already boosted your projectile out to supersonic, what need do you have for a 2nd stage jet device? Also, you would be generating recoil.

 

[Novus Collectus]

Herein lies your problem. If you have already boosted your projectile out to supersonic, what need do you have for a 2nd stage jet device? Also, you would be generating recoil.

I already said, to possibly either extend the range by keeping the bullt up to speed for longer, or to increase the speed without increasing recoil.

 

[Spencer5883]

Sounds like a good idea, but the speed of sound is 1,125 ft per second in air at room temperature.

 

[Zoogster]

Certainly possible. I have thought of many cool bullet ideas. The biggest barrier is cost per round. People have an idea of what a round should cost, and if you go double triple, or 10x that to have enough quality control to mass produce a reliable design you will go broke.



There is some other major legislative hurdles to many unique bullet designs. One is the federal law against explosive payload over a specific amount. Now this may be designed to prohibit your typical HE rounds, but the wording of the law could prevent you from putting enough propellant in the round to run an engine.

The other major law is the one against armor piercing handgun bullets, which the ATF applies to any caliber ever commercially chambered in a handgun, including most rifle rounds at their discretion.
This law could easily make it illegal to use steel or most other materials with a high enough tensile strength to resist deformation during typical storage and use to still reliably work with precision.
Typical metals used in ammunition are soft, and deformation of such an engine even a to a small degree would have serious effects on the propulsion created and whether it flies way off target.




Beyond just the law you have the issue of increasing the dimensions of the round to hold something with much less density like energy dense propellant. This means a projectile with more air resistance with lower total mass than lead would have. So even if it increased performance, the loss in total mass of a bullet of a certain size would counteract some gains over longer shots where such a thing might have benefit.
Heavier bullets retain energy at range better. But a round increasing its velocity will compensate and could certainly exceed typical performance.
You would need to make a graph to determine gains and losses and what the trade-offs are.
However I think the data would show a much cheaper conventional round that simply has more weight left behind (brass and burned powder in the form of residue and gas) is quite efficient compared to one that takes even some propellant along. Adding more propellant in the brass left behind will increase gains much more easily than adding dimension to and lowering the density of the projectile.


Another major issue is propulsion will disturb the fired projectile. So it would have lower accuracy than your typical precision round. Your typical round exits the rifle and then has a smooth relatively undisturbed trip to the target. Just gravity and air resistance to contend with. But with propulsion it will have additional forces that can cause deviation from initial point of aim.
It could compensate by having electronics, fins, and a guidance system that always goes where it was aimed when fired, but now you just made it way out of budget for minimal gains.
You could easily create bullets that cost several thousand dollars each with their own microprocessors and sensors.
Maybe some anti will find a way to require "smart bullets" in the future to put affordable ammo out of reach of 99.99% of the population.

 

[Ky Larry]

What would be the purpose of the round? We can already accurately fire regular projectile out to the limit of our vision. What would be the purpose of extending the range out to several thousand yards? You would need spotters to control and correct aim and we can already do that with artillery. Technically, I suppose it could be done, but to what purpose?

 

[Zoogster]

What would be the purpose of the round? We can already accurately fire regular projectile out to the limit of our vision.

Not typically with a hand held firearm.

The horizon is the limit of our vision with the use of optics, and the horizon is just over 3 miles away at sea level. Even more if you are at elevation from the target.

3.1 miles away is 5,456 yards. Twice the longest recorded sniper kill.

 

[Ky Larry]

Good points, Zoogster. However, current projectiles will travel over 3 miles. The problem isn't getting a projectile to travel that far, but, as you suggested, hitting hitting your target. I see what you're saying. This round would be more accurate due to a flatter trajectory but any movement by the shooter would be magnified over distance. As range increases, accuracy decreases.

 

[Manco]

Sorry to be a killjoy, but it's complicated for what it is, costly, and unnecessary in the general case.

 

[hammerklavier]

It would likely have terrible accuracy. First, putting a good stabilizer on the bullet would be difficult. Spin alone would not do it, and sabots don't spin bullets very well anyway. Then, as the engine catches, it would get nudged off-course and again as it sputtered out of fuel. Also, as a rifle bullet, it would have very low grain weight to make room for the fuel.

 

[SaMx]

a bullet is way to small to have a jet engine inside it. even a ramjet, like you described, needs fuel, and you aren't going to be able to carry enough fuel for more than a tiny fraction of a second of burn time. By the time you get big enough to carry enough fuel for realistic burn time and range, you've made a missile, not a bullet.

 

[MisterMike]

Interesting . . . at least theoretically. However, wouldn't solid fuel rocket technology be more appropriate to this type of an application?

I have to say though, that I don't think that this type of a round would long survive the political process. Even if there were legitimate uses, it would be vilified as a super-killer bullet.

 

[Chemistry Guy]

I have thought about this topic a lot, and I came to the conclusion that it would be more practical to make the projectiles rockets (carry their own oxidizer) rather than jets (using oxygen from air). I think something like lithium perchlorate, ammonium perchlorate, or even ammonium nitrate could be used as a solid propellant.

The problem with a jet engine that small is that the fluid dynamics don't scale very linearly. With holes that small, the Reynolds number, or ratio of inertial to viscous forces, would be too small to get turbulent flow, and using laminar flow, diffusion is too slow to adequately mix a fuel and oxidizer unless the fuel was a very high pressure gas, which would be a huge engineering challenge.

Still, I think it sound like a really interesting idea for artillery shells.

 

[ForumSurfer]

For the price per kill at long distances, a .50 cal is a bargain. As others have said, you'll be limited by horizon. It would be far cheaper and more prudent to just close the gap slightly and use a dead reliable .50 BMG. For the price of development, research and production of something like you mentioned...you could have already dropped a smart bomb on the guys head from a navy fighter or a drone several times over.

As others stated, the Gyrojet was a similar, failed design. It made for some neat looking rounds, though. The range and dependability were severely limited. It made for some neat looking rounds though!

 

[3006mv]

http://www.securityarms.com/20010315/galleryfiles/2600/2699.htm

 

[Ian Sean]

Such a small projectile would see little benefit over conventional ammo, as the old gyro-jet showed.

But the military diddled with these munitions off and on, notably the navy trying to increase the range of naval guns.

Link to 1968 article on RAP munitions Page 84 scroll down: http://books.google.com/books?id=D9QDAAAAMBAJ&pg=PA84&lpg=PA84&dq=navy+16%22+rocket+assist&source=bl&ots=6JOar34Wxg&sig=FE4lsVoPqVRN2J5rT7qiE5JaL4U&hl=en&ei=WarZS-SEMZW09gS1oZlm&sa=X&oi=book_result&ct=result&resnum=2&ved=0CAoQ6AEwAQ#v=onepage&q&f=false

 

[Jim Watson]

It has been done... on artillery shells. Read about Rocket Assisted Projectiles.
But I agree with Chemistry Guy, the scaling factors are all against you.

A related development, the Base Bleed Projectile, might work. An article I Googled said even a standard tracer has 9% less drag than a plain bullet, because the trace also reduces the low pressure area at the base of the bullet.

 

[Deanimator]

During WWII, the Germans developed a ramjet artillery shell. It went nowhere.

As pointed out elsewhere, without a guidance system and an effective means to alter its course, the initiation of the onboard propulsion system virtually guarantees inaccuracy.

And in a smallarms projectile there isn't enough space for an effective propulsion system (including fuel), guidance system and payload.

 

[CoRoMo]

gravity

Without anything to provide lift, it will still begin to drop to the ground once it exits the muzzle.

 

[NOLAEMT]

I say go for it... if you can make it work, even a little, you'll be a very wealthy man.

 

[Justin]

It probably wouldn't work, but it would be interesting to see the numbers run nonetheless. Start with an assumption of, say, a .50 projectile, and calculate the energy needs to keep it at a sustained velocity of say, 3,000 fps. From there you should be able to figure out what the fuel requirements would be, and whether or not it would be feasible to design such a round based on how long the fuel would last vs. how many milligrams of fuel you could reasonably expect to carry in a round constrained by the volume of a typical 50 BMG bullet.

 

[fireman 9731]

I have had similar thoughts... Interesting idea...

The biggest problem I see is being able to accurately thrust...