A Sonic-Crack Theory

[HollowPoint]

I wasn't sure exactly where to post this particular subject but, since it will be a future project for me I decided to put it here.

One of the luxuries of being an Ignorant No-Engineering-Background kind of guy is that it allows one to think outside the box when it comes to dreaming of ways to accomplish something that the experts say can't be done.

I'm not an engineer or a machinist, and I'm not an accomplished CAD/CAM software kind of guy. I'm just a No-Name-Goober with a computer, some machinery and a million ideas with not enough time in the day to bring the vast majority of those ideas to fruition.

For the longest time I've dreamt of building my own rifle suppressor but, I have yet to accumulate the expendable funds to apply for my tax stamp.

I already have my design worked up in my brain. It's just a matter of getting all my other ducks in a row; so to speak. I have the metal working machines to do the work and I have the design software to draw up my schematics; it's just that there are so many other things that are more important than a new rifle suppressor right now; or in the foreseeable future for that matter. As a result, I've had to repeatedly put this particular dream on the back-burner.

As is always the case for me and my ideas, one project tends to lead into another project that will hopefully enhance the previous project. It's just a vicious cycle. This future suppressor project is no different.

With this suppressor project in mind, I've been wondering how I might make an efficient suppressor even quieter to shoot without going to "Sub-Sonic-Loads?" I've done alot of informal research on the internet and most of what I've come up with has been hear-say; just folks repeating what they've read or heard somewhere else and passing it off as personal experience. I know this to be true because much of what I've read from various sources is the same word-for-word text I've read from the original authors.

From what I've been able to gather, I think I've comeup with a new suppressor-baffle design; I mean, different from anyone else's. I won't know if it will live up to the expectations that I've dreamed of until I actually put it together though.

Having said this, if my suppressor design does turn out to be as efficient as I dream it will there is still the matter of the "Sonic-Crack" that generally works against the small percentage of the noise suppression gains that a good suppressor achieves.

So, here's the real reason for this post.

I've come up with an "Outside the Box" theory about eliminating or at the very least, mitigating the "Sonic-Crack" of full power "Super-Sonic" loads.

First off let me say this; I have it on good authority that, "There Is No New Thing Under The Sun" so, who knows, this idea may have very well already been tried and failed but, in my informal research I wasn't able to find any evidence of such attempts other than bullet coatings similar to the paint used on Stealth aircraft having been tried. (which didn't even come close to addressing the root cause of "Sonic-Booms/Cracks.)

If you've ever searched for information on what exactly causes a "Sonic-Boom" or a "Sonic-Crack" in the case of a bullet flying through the air; to put into the simplest of terms I can think of, it has to do with the pressure waves that stack up ahead of our bullets traveling through the air at "Super-Sonic-Speed."

In trying to figure out a way around the friction and air-resistance that our "Super-Sonic" bullets encounter while in flight, I couldn't come up with any ideas to counter the air resistance. In attempting to do so, I came away with a better understanding of why the experts say it can't be done.

But, being the Ignorant-No-Engineering-Background kind of guy that I am, I decided to come at it from a different angle.

In order to simplify the explanation of my solution for this "Sonic-Boom" phenomenon I'll use the following analogy so that I make a little more sense; I hope.

Picture the tunnel-boring machinery used to dig underground tunnels for subways or trains and such. If engineers had used a long sharp very-low-drag metal rod with a hydraulic press to push it forward to overcome the friction and resistance of the earth they were tunneling through, how far and how fast would their progress be?

Even our most efficient conventional bullet designs meet the same type of resistance when they fly through the air at "Super-Sonic" speeds. And this is in spite of the fact that air-molecules are alot less dense than the earth that the earth-moving equipment encounters.

I have yet to machine any prototypes of this bullet design so I can't even say for sure if it will work or not but, the premise of my theory is that my bullets won't be slicing through the air as with conventional bullet designs. They'll be boring through the air using both the forward momentum (fps) that the propellant gases impart and the rotational momentum that the rifling imparts. (rpm's)

This is an overly simplified explanation of course but, I'm hoping you get the idea of what my theory is based on.

Although any prototypes I make will be done using brass or copper rod, even with cast bullets traveling at the lower end of the "Super-Sonic" spectrum (in a 30 caliber for example) the RPM's are many times faster than the velocity/FPS's. The Impeller-Affect of my theoretical bullet design (Not Propellor but Impeller) -in theory- should bore through the air that would have otherwise stacked up ahead of the "Super-Sonic" projectile and thereby mitigate or possibly even eliminate the "Sonic-Crack."

The image below is NOT to scale. I drew it up to give you an idea of what I'm trying to explain. The configuration of the Impeller-Fins (height, pitch, number and length and angle of the boat tail) would have to be calibrated to the RPM's of the bullets in flight so that they suck air faster than the pressure waves can stack up ahead of them.

Wether you believe it to be plausible or not is your business. I do intend to test my theory at some point in the future. My reason for posting this potentially laughable theory was to show those here who may be trapped inside the proverbial box that there's a whole lot more to cast bullets than what's visible from inside this cast-bullets-box. You just have to look for it.

You just have to dream it up. If it actually worked it would be "Ground-Breaking." If it dosn't work, so what! At least somebody tried.

HollowPoint

[W.R.Buchanan]

Looks like the Screws on the Nautilus.

The bullet and the pointed example you gave above both "displace" the medium they are traveling thru. AS opposed to the boring machine which is grinding up the material on the face of the cutting surface and transferring it to behind the machine for disposal.

Your bullet shown above does exactly the same thing is just has vanes as the first example (but will displace even more media due to the mass of the fins.) to help it screw it's way thru the air.

The displacement occurs either way. You can't break the sound barrier with out physically breaking the pressure wave. You can't just slice thru it, even trying to push a knife edge thru the barrier,,, still breaks the barrier.

If you listen to the various types of reports from different caliber guns you will see Pop, crack, really loud earsplitting crack, pow, and BOOM. The speed at which the barrier is broken and the frontal area of the projectile govern which type of noise you get. IE: big and slow = BOOM! Very fast small dia. = earsplitter. Fill in blanks with your own experience.

I am not in any way telling you to not try what you are attempting. You never know it may work, plus that, I might be FOS!

Randy

[HollowPoint]

"I am not in any way telling you to not try what you are attempting. You never know it may work, plus that, I might be FOS!"

In my mind's eye I see it as being plausible. And I know that I may very well be the one who's FOS.

The Nautlis example is pretty good. Although it was a fictional submarine, it did drill thru the water in the same manner that I envisioned this bullet design drilling thru the air; minus the audible shock wave.

Successful or not, I do intend to try it. It's a design that can actually be tested on the bench-top by turning scaled up versions of the same design. This will confirm the plausability. This will also let me tweak the Impeller-Fins to the angle and shape that will displace the most air for a given velocity.

But, I'm getting ahead of myself now. I still have to finish my present projects.

Wether it works or not, I'll make it a point to let you all know.

HollowPoint

[gspgundog]

Keep us up to date as you progress, sounds very interesting to another "Ignorant-No-Engineering-Background" guy who knows he is Foxtrot Oscar Sierra. lol

[koehlerrk]

OK, HollowPoint... time for a physics lesson. Well, a couple, and some fluid dynamics too.

In laymans terms, what causes a "sonic boom"? Contrary to popular thought, it is NOT caused by an object traveling faster than the speed of sound. Rocket, airplane, bullet, the object does not cause the sonic boom. Time to back up a step.

When traveling sub-sonic, air can freely move around an object, rather like water flowing around a boat. Now, the faster you go, the faster the water has to move to get out of the boats' way. Eventually, it can't move out of the way fast enough and piles up to both sides. (Real world, it gets displaced all around, but both sides is good enough for this lesson.) Now, when something is moving faster than most boats can dream of, something very strange happens. The water behind the boat gets blasted so far out of the way that it forms a vacuum behind the boat. When the water rushes back in, the vacuum bubble collapses, and we get a very loud noise.

Air can be thought of as just very low viscosity water. At high enough speeds, the effects are similar. So, the bullet pushes the air out of it's way, and a vacuum forms behind it. When the air rushes back in to fill the vacuum, the air from one side collides with the air from the other side, which is heading in the opposite direction, and we get a miniature head-on collision. That is the sound you're hearing.

To date, no one has developed a way to eliminate this effect. However, keep thinking about it, and who knows, you just might be the one who solves it.

[wv109323]

I would like to see you try it but I think what you have designed is a rotational wing. Today's un-finned bullets create a slight pressure differential from the top to the bottom of the bullet. This pressure differential creates a slight yawl in the bullets flight. I think your design will magnify that effect many times over and un-stabilize the bullet. But what do I know.
Boring machines do not "pull" themselves into the material being cut. The rotating drum with cutting bits is pushed by a traction system of the machine. The heavier the machine the more traction or pushing effect the machine can generate. There is no such thing as a small boring machine that bores a big hole.
I have seen an idea somewhat like yours. The Army was looking at smart bullets. The bullets would be finned with a means to adjust the fins. The bullet would have a camera. The bullet would be fired and then the fins adjusted ( via a controlling device) to "steer" the bullet into the intended target. Of course the camera would be used for forward looking.
Staying inside the box gets boring. Do you by chance read the National Inquirer?

[W.R.Buchanan]

From "the League of Extraordinary Gentlemen" the Nautilus from that movie had screws like your bullet.

Just saw it again last week.

The first underwater marine propellers looked like large wood screws. This is how they got the name "Screws."

First thing I thought of when I saw your picture.

Randy

[leeggen]

Hollowpoint you might contact Oldpara from "Phillips anyone" I beleive he has a bullet shape that screws in the same rotation as the twist. He plays alot with different designs of bullets just for fun. He might just beable to produce it for you or help some.
CD

[waksupi]

Keep on thinking. You're not the first guy here who has tried to beat physics. No one has been successful yet, but give 'er a shot! [smilie=p:

[Oreo]

What about an exagerated boat tail bullet where the boat tail is an inch or so long and goes almost to a sharp point? Granted, gyroscopic stability would be a serious issue but just in terms of reducing the "vaccuum bubble collapse / head-on collision" thing, it would be more helpful.

[huntincowboy]

If you watch this video https://www.youtube.com/watch?v=OubvTOHWTms&feature=youtube_gdata_player from 3:27 you can see a pretty good representation of what's going on. It's the pocket created behind the bullet and the stacked air (water) rushing back in. When the bubble collapses, this is where the boom comes from. Water is nearly incompressible, far more viscous, and represents far more mass than a similar volume of air so the bullet isn't likely moving supersonic in the video, but the bubble is clearly visible. If you look on YouTube at jets and stuff and maybe look into some video captured by a Schlieren device maybe you can further develop your ideas. Good luck! Keep us updated!

[220swiftfn]

What about an exagerated boat tail bullet where the boat tail is an inch or so long and goes almost to a sharp point? Granted, gyroscopic stability would be a serious issue but just in terms of reducing the "vaccuum bubble collapse / head-on collision" thing, it would be more helpful.

Saw something like that in an old American Rifleman (in their "75 or 100 years ago" section.) It was a sabotted round that looked pretty much the same from the front as it did from the back. Kinda like someone melded two Sierra Matchkings, the rear ogive starting where the boattail would be, with a bored hole completely thru the center. IIRC, this was an attempt to drastically improve the ballistic coefficient to gain range. Unfortunately, it proved to be VERY unstable.....



Dan

[jmorris]

I think your bullet could make some neat noise on its own.

Are your vanes going to match the twist of the rifling?

You gave me an idea. What if you hollowed out a bullet like the old "cookie cutter" PMC Ultramag bullets from the '80's (that were discontinued because the idea was already patented http://patent.ipexl.com/inventor/Abraham_Flatau_1.html) and put a whistle in the center. Then your suppressed shots could sound just like the movies.

Don't laugh too hard, there are people buying "zombie" ammuntion these days...

[Artful]

https://www.youtube.com/watch?v=cp5gdUHFGIQ
AK in air with schlieren photography
http://www.divshare.com/img/5690435-008.jpg

NASA attempt at minimizing the sonic boom for supersonic flight
http://www.nasa.gov/vision/earth/improvingflight/supersonic_jousting.html
http://www.nasa.gov/images/content/160005main_quietspike_flight.jpg
http://www.nasa.gov/images/content/160004main_quietspike.jpg
boom extends to start the smaller sonic bow wave so that the rest of the jet is inside of it

[jmorris]

"Outside the box" bullet designs are not new. Some, like the hollow point or conical bullet become quite popular. Other designs don't make it much further than paper. http://www.google.com.mx/patents/US4665827

[dudel]

Air can be thought of as just very low viscosity water. At high enough speeds, the effects are similar. So, the bullet pushes the air out of it's way, and a vacuum forms behind it. When the air rushes back in to fill the vacuum, the air from one side collides with the air from the other side, which is heading in the opposite direction, and we get a miniature head-on collision. That is the sound you're hearing.


Interesting. What if the bullet looked like a ring or tube, with a wad in the base to contain initial pressure, drop off (like a shotshell wad). Would there be less displacement since there would be flow through the bullet?

I have absolutely no ideas if this would be stable or what effect it would have if you could hit a target with it. It would certainly be light.

[HollowPoint]

In answer to some of the questions posed in your replies; yes, no, maybe and I won't know until I try.

I'm not trying to change the laws of physics. I'm just trying to apply them in a slightly different way that most are used to.

Trying to reinvent the wheel, You Can't Change the laws of physics, Just because it looks like it might work doesn't mean will. Are there any more cliches out there that we can get out of the way right up front?

Virtually all the information posted in these replies is some of the same information I came across while doing my informal research; including the videos. In fact, it was that AK youtube video shooting under water that kind of gave me the ideas for this theory.

It kind of makes me happy to see that most of us are on the same page. It means that my feeble attempt at explaining my theory made just a little sense to some of you.

I'll keep plucking away at it as time permits.

HollowPoint

[Sensai]

Just wandering aimlessly through my mind, but if the whole projectile is traveling super-sonic then to do any "digging" the vanes will have to be the first part to enter the air. Otherwise they will be covered by the wave front created by the nose and not have any exposure to the compressed waves. They would also need to have the equivalent of winglets to prevent shock wave escape from the outside edges. Of course winglets would produce a wave front that would obscure the "digging" vanes again. My head hurts!

[Willbird]

If it is actually cavitation (and I think it might qualify) then the effect is a LOT bigger than the bullet itself.

Bill

[Bent Ramrod]

I was always taught that the sonic "boom" is the shock wave that forms at the front of the moving object when it reaches the Mach number for the medium it is going through. A similar wave also forms wherever a leading surface on the sides can build up such a wave. You can see them in spark (and more modern) photographs in wind tunnels as a "stern and bow wave." The cavitation behind the projectile is just a minor disturbance compared to this. As far as I know, there is no way to avoid this; if it was a matter of cavitation, jet planes would be as quiet going through the sound barrier as muffled blade helicopters and people living near air bases would complain less to the base commanders.

That bullet design is pretty interesting, though. Might make an interesting whistling noise (perhaps supersonic for most of the flight).

[markinalpine]

How about a sabot to hold the bullet when it is in the barrel and to provide a gas seal, while the bullet has an axial through hole to allow the air to pass from the tip to the base after the bullet exits the barrel and the sabot drops off?
Just a thought! :veryconfu
Mark :coffeecom

EDIT: I remembered I had this picture uploaded already!

82925

[williamwaco]

Hate to be a party pooper but the US Government can't do it with airplanes.

Even the most advanced stealth airplanes have to fly sub-sonic to be quiet.

[fouronesix]

Hate to be a party pooper but the US Government can't do it with airplanes.

Even the most advanced stealth airplanes have to fly sub-sonic to be quiet.

Yep, me too and hate to be another party pooper. No way around it. ANY KIND or SHAPE of solid object that travels super sonic through the air will generate a "sonic" compression wave with the resulting sound. Additonally, the bullet is not the only thing that produces a sonic "crack" when fired. Even if the bullet leaves the muzzle a little sub sonic, the gasses leaving the muzzle, just as the bullet leaves, may be super sonic and can also emit the "crack".

[huntincowboy]

Yep, me too and hate to be another party pooper. No way around it. ANY KIND or SHAPE of solid object that travels super sonic through the air will generate a "sonic" compression wave with the resulting sound. Additonally, the bullet is not the only thing that produces a sonic "crack" when fired. Even if the bullet leaves the muzzle a little sub sonic, the gasses leaving the muzzle, just as the bullet leaves, may be super sonic and can also emit the "crack".

I think OP was talking about developing a bullet that would allow the maximum reduction of sound with supersonic ammo fired from a suppressor.

[salty dog]

You gave me an idea. What if you hollowed out a bullet like the old "cookie cutter" PMC Ultramag bullets from the '80's (that were discontinued because the idea was already patented http://patent.ipexl.com/inventor/Abraham_Flatau_1.html) and put a whistle in the center. Then your suppressed shots could sound just like the movies.

Don't laugh too hard, there are people buying "zombie" ammuntion these days...

You could us those deer whistles that you install on your bumper and are supposed to alarm the deer so much that they flee in terror. Just put the whistle in backwards and the deer would be irresistibly drawn to the shot. Presto! self guided deer bullets.

[Gibbs44]

Good luck in your endeavor sir, it should be an interesting project getting a bullet into that shape to say the least.

Artful, that was probably one of the coolest videos I've ever seen, thanks for sharing that.

[fouronesix]

I think OP was talking about developing a bullet that would allow the maximum reduction of sound with supersonic ammo fired from a suppressor.

Thought the thread was open to all ideas. No? Successfully suppressing a large caliber rifle round will require at least a large coffee can or larger size suppresser. Forget the finned bullet- the engineering of that will take all the skill and knowledge few have plus a lot of blown up parts during the "testing" process.

So to the finned contraption bullet. How in the world would putting fins on the nose of a bullet reduce sonic crack- no matter if the fins are pitched to push or pull through the air based on twist rate of the bore??? The exposed nose of the bullet will generate a compression wave PLUS each leading edge of each fin will have it's own compression wave. Even if a finned or hollow or corkscrew or cubic or sprinkled with fairy dust or whatever supersonic bullet in combination with some suppresser reduced sonic crack, I bet it would be a tack driver :) Sorry I entered this thread.

[Artful]

Successfully suppressing a large caliber rifle round will require at least a large coffee can or larger size suppresser.

NOT that large really - 7.62x54R M38 Mosin Scout with AAC Cyclone .308 can.
http://img.photobucket.com/albums/v355/rowdyfisk/Misc/th_0612112302.jpg (http://smg.photobucket.com/user/rowdyfisk/media/Misc/0612112302.jpg.html)
click pic to enlarge

[jmorris]

You could us those deer whistles that you install on your bumper and are supposed to alarm the deer so much that they flee in terror. Just put the whistle in backwards and the deer would be irresistibly drawn to the shot. Presto! self guided deer bullets.

Now, that is thinking outside the box.



Successfully suppressing a large caliber rifle round will require at least a large coffee can or larger size suppresser.

No, my 458 socom suppressor is only 2" in diameter and it makes less noise than my factory (AAC) cans.

http://i121.photobucket.com/albums/o213/jmorrismetal/can/DSC02435.jpg

It does have a lot of volume but to keep it short(er) it telescopes back over the barrel.

http://i121.photobucket.com/albums/o213/jmorrismetal/can/sxsxs.jpg

[Artful]

Have your guys seen this test chart with 308 caliber bullets?
http://img.photobucket.com/albums/v355/rowdyfisk/Misc/Hartikka_bullet_noise_graph.gif (http://smg.photobucket.com/user/rowdyfisk/media/Misc/Hartikka_bullet_noise_graph.gif.html)
Notice they tried two different conventional bullet shapes to see if it made a difference in sound signiture - it didn't at supersonic speeds.

Smaller projectiles at supersonic speeds make smaller sonic booms
larger projectiles at supersonic speeds make larger sonic booms....

Using same suppressor with 7.62x51, 7.62x54R and 243 - the 243 is quieter even though the baffles in the can are less efficient because the 243 bullet makes a smaller sonic boom.

[Artful]

Nice .458 SOCOM project is the can a Form 1 then?

[huntincowboy]

Thought the thread was open to all ideas. No? Successfully suppressing a large caliber rifle round will require at least a large coffee can or larger size suppresser. Forget the finned bullet- the engineering of that will take all the skill and knowledge few have plus a lot of blown up parts during the "testing" process.

So to the finned contraption bullet. How in the world would putting fins on the nose of a bullet reduce sonic crack- no matter if the fins are pitched to push or pull through the air based on twist rate of the bore??? The exposed nose of the bullet will generate a compression wave PLUS each leading edge of each fin will have it's own compression wave. Even if a finned or hollow or corkscrew or cubic or sprinkled with fairy dust or whatever supersonic bullet in combination with some suppresser reduced sonic crack, I bet it would be a tack driver :) Sorry I entered this thread.

Sorry I wasn't trying to upset anyone, I'm just saying that if the gasses are supersonic or not doesn't matter much in the OP's case because the suppressor takes care of that.

[HollowPoint]

Just wandering aimlessly through my mind, but if the whole projectile is traveling super-sonic then to do any "digging" the vanes will have to be the first part to enter the air. Otherwise they will be covered by the wave front created by the nose and not have any exposure to the compressed waves. They would also need to have the equivalent of winglets to prevent shock wave escape from the outside edges. Of course winglets would produce a wave front that would obscure the "digging" vanes again. My head hurts!

I'm not sure but I think that you're not taking into account the ultra-high RPM's that the rifling will impart on the bullet and the "Impeller" action that the fins will produce. This is why it will be critical to find the correct pitch for the "Impeller-Fins."

Try calculating the RPMs on your fastest moving cast lead projectile fired from a standard 1 in 10 twist 30 caliber barrel with the bullet moving at about 1800 fps. Then do the calculation using a 168 grain bullet traveling at about 2700 fps out of the same 1 in 10 twist barrel. Those fins are rotating far faster than the bullet is moving forward.

I think if the fins are correctly calibrated, the suction that they'll induce at the front of the bullet; even one traveling at 2700 fps, will be enough to lessen or eliminate the pressure wave that stacks up ahead of the bullet and eventually slips back and collapses at the base of the bullet.

This is just how I picture it in my mind. Right now there's no telling if it will really work. I'll just have to try it first.

HollowPoint

[freebullet]

Wow sweet setup on the458. By looking at the underwater shoots you could figure to get MAXIMUM effect you would need a massive unwieldy suppressor. It's always a balance of size & weight to make it quiet. If the 458 muffler was 8" round & a foot longer it may be almost silent but who would carry it. Maybe add wheels & a kickstand.

[calaloo]

They said it couldn't be done
So he smiled and set right to it
And after many weeks of ardious work
He found he couldn't do it.

[jmorris]

Yes, the 458 can is on a form 1, there are some more photos of it here http://s121.photobucket.com/user/jmorrismetal/library/can?sort=6&page=1

freebullet, for max effect you would be inside a room and just shoot through the wall. If you can control the exit airflow you can compress the air inside the can much more than water can control the air pressure.

On the other hand, if you fill a steel container with water and freeze it, water in that state will often split steel. So you need someone to freeze themselves and an AK in a pool solid then post the video, I bet it looks a lot different...

[Artful]

Wow sweet setup on the458. By looking at the underwater shoots you could figure to get MAXIMUM effect you would need a massive unwieldy suppressor. It's always a balance of size & weight to make it quiet. If the 458 muffler was 8" round & a foot longer it may be almost silent but who would carry it. Maybe add wheels & a kickstand.

Bigger doesn't make quieter all the time - the baffle designs have to work the gases to exchange the energy into heat to reduce the sound signature, look up suppressed airguns and watch a view video's and you'll see even without gunpowder burning you have projectile noise.

If you had a "boom" on your boolit, like the jet in the Nasa pic - you might lessen the noise but getting the boolit to stabilize will be the trick.

[BNE]

1st: Artful - GREAT video of the shots under water. I pulled my kids over to view them as a great tutorial.

2nd: HollowPoint - Do not limit yourself because you do not have a fancy piece of paper stating you have a degree. I have one of those pieces of paper. It does not do the work or you. Unfortuneatley most Engineers are quicker to tell you why your idea won't work, than to try to help your idea work. More good ideas get killed before they get started because an Engineer states it can not be done. My best bosses over the years have let me try crazy ideas in order to let me learn what works and what does not work based on experience. Degrees are nice and yes, very helpful, but you learn more from failure than from success. (As long as you don't give up!)

PS - As an engineer, I think your current drawing will not work. :groner:

[Artful]

I'm with ya BNE - but I'd say try a stick stuck in a hollow point and see if it has a noticeable difference.

NASA did F5E with a knife nose and it did have a measurable drop in sonic boom noise
http://upload.wikimedia.org/wikipedia/commons/thumb/6/6b/F-5E_Shaped_Sonic_Boom_Demonstration_aircraft.jpg/220px-F-5E_Shaped_Sonic_Boom_Demonstration_aircraft.jpg
but that's not going to work with a rotating projectile !

http://www.spacedaily.com/images/plane-quietsonic-bg.jpg
Northrop Grumman Unveils Concept For Quiet Supersonic Aircraft

I don't think the active isentropic air inlet and extensive laminar aerodynamics
is going to be possible in a cheap to shoot boolit either...
http://www.spacedaily.com/news/plane-sonic-02b.html
http://www.faa.gov/about/office_org/headquarters_offices/apl/noise_emissions/supersonic_aircraft_noise//media/2-Panel2-Komadina-Northrop.pdf

[Skunkworks]

Here is a pic of a shockwawe.
82991
As you can see the wawe starts at the point and anything under it is "hidden", so your "impeller" is useless.

Secondly there is rotational speed.
The pitch og the impeller might be tuned to the rifling pitch but remember that a bullet fired looses actual speed much faster than rotational speed.
In other words: It might work at muzzle but after a short time the "impeller" will start to rotate faster than forward speed and cavitate big time.

Here is something to read about aerodynamics:
http://waterocket.explorer.free.fr/aerodynamics.htm

[Artful]

http://lol54.ru/uploads/posts/2010-01/1263979181_bullet2.jpg
http://www.visualphotos.com/photo/1x6063937/schlieren_photo_of_a_bullet_passing_through_hotair _h630008.jpg

http://www.ivorbittle.co.uk/Books/Fluids%20book/Chapter%2014%20web%20docs/The%20flow%20round%20a%20bullet_files/image034.gif

http://www.ivorbittle.co.uk/Books/Fluids%20book/Chapter%2014%20web%20docs/The%20flow%20round%20a%20bullet_files/image036.gif

http://t0.gstatic.com/images?q=tbn:ANd9GcQJPcL-gQA_EzHxUP4Y8pbaomjaJfLuca4mJBieQGCUckcmLkpu
Notice on this wadcutter the build up of air in front of the flat nose make it's own wave
because it's acting as a solid.

http://bulletin.accurateshooter.com/2013/04/berger-bullets-introduces-revolutionary-sonic-ripple-bullet/
http://accurateshooter.net/Blog/ripple03.jpg
notice even the small meplat shows a build up of air between shock wave and bullet.

The holey Bullets seem to have disappeared
http://images.gizmag.com/hero/compbullets.jpg
this was the "Comp Bullet" - an Italian company design
many claims for it magical holiness.

[HollowPoint]

You know what would be really funny? If in the end, I was able to get my uneducated theory to actually work. That would be hilarious to me. I think that, that reason alone is enough to make an attempt worth while; even if it's just another failed attempt at something that's already been tried.

I can see why many would state or agree that such a cockamamy idea wouldn't work. And, when viewed or attempted from the perspective of their education, experience or whatever, they're most likely right. It's destined to fail before it's even started.

I don't view it from inside the same box that their viewing it from. In spite of this I'm under do illusion that the "Box" I'm working outside of is any more or less conducive to reaching a successful end of such a project. I think it's just a matter of one person viewing things from a different perspective that another.

HollowPoint

[Artful]

Ok, so what's the easiest way to trial your theory? - first calculate the twist needed on your fin's, then find a lathe or screw machine that's free to play - make it out of copper, brass or bronze I'd say as lead isn't very machinable. What can we do to help?

Looking at your original post do you have a gain twist on the wings/fins - what do you want to call them?

[jmorris]

You need to hook up with the guy in a forum up top that has made tons of custom molds of all sorts of designs. IIRC he had little houses on top, some looked like driver tips and I think he was even working on a screw mold at one point.

[jmorris]

This is his thread.

http://castboolits.gunloads.com/showthread.php?181398-phillips-head-anyone

[Artful]

Excellent - I remember that thread now -
http://castboolits.gunloads.com/showthread.php?181398-phillips-head-anyone&p=2407591#post2407591

[leeggen]

Gee guys that is what I suggested in the beginnig. "Phillips head anyone" by OLDPARA He is pretty sharp onthe programs and design of some fantastic art style bullets that do shoot pretty well.
Hollowpoint I say go for it and I hope you suceed and prove some doughter wrong. Even if you don't suceed completly you will have further imfor. to try again with an adjusted design. As one of my old boss's said" I may not always be ALL right ,But I will never be ALL wrong!!!
Good luck
CD

[jmorris]

Sure enough, right there in post #8. I didn't remember the Op's name or the name of the thread, until I found it again.

[leeggen]

He even made one on a suggestion that had threads on it. I beleive it was about a 5/16s tap in size. Be interesting to see the air wave off of it! I would think if it shoots a reasonable group and has a lower noise level then Hollowpoints design could be considered a success, yes or no???? We all would learn something from it anyway.
CD

[jmorris]

The threaded mold part is page 5 starting around post 87 or so.

[HollowPoint]

Ok, so what's the easiest way to trial your theory? - first calculate the twist needed on your fin's, then find a lathe or screw machine that's free to play - make it out of copper, brass or bronze I'd say as lead isn't very machinable. What can we do to help?

Looking at your original post do you have a gain twist on the wings/fins - what do you want to call them?

The image and the analogy I posted are just that; just and image to give you an idea of what my theory is based on. The tunnel-digging analogy was just to paint a mental picture but, some have taken these examples far to literally so it's no wonder there's so much doubt surrounding my theory.

I do envision the initial prototypes being machined from brass or copper rod but, for the bench testing this won't be necessary. I planned on turning a one inch piece of delrin rod to the desired bullet profile, attaching adjustable Impeller-Fins so that I don't have to turn a new example with every degree of adjustment I make to the fins.

I have air tools that spin at real high RPMs. I can adapt one of them to spin my mock-up in order to adjust the fins on the Impeller section of my bullet to the optimum air-flow position. This can be done by mounting this test-bullet inside an enclosure with a small viewing window. Smoke or water can be used as the medium to simulate the movement of air flowing around and past the bullet.

Once the proper pitch is established for the Impeller-Fins, I can then move forward to calculating with mathematics what I can expect when or if the bullet is moving forward at a given velocity and at a given rate of spin.

The tail end of my delrin mock-up-bullet will have the heel threaded so as to be able to screw on different boat-tail lengths or angles. Again; this is so that I don't have to turn a new delrin mock-up bullet in order to hit on the right length or angle for the boat tail heel. It should be just a matter of making up boat tail heels that I can quickly swap out until I get the optimum configuration. Even better still might be the use of an old antenna-type of set-up that consists of various diameter hollow rods; one fitting snuggly inside the other mounted on the heel of my mock-up and just sliding them in or out to the optimum length.

Right now I'm just telling you the steps that I hope to go through as I envision it in my mind; not what I've actually done so far. I don't see it as being as complicated as many seem to believe. Maybe it's because I'm just to much of a simpleton.

In my mind, the price of success and the price of failure are exactly the same. We all know that failure is easy to achieve. From this point of view, achieving success should be easy; provided you go about it correctly.

Even with what I've written up to now, I've gotten way, way, way ahead of myself. I still have to finish the final stages of my Boat-Tailed Gas-Checks project and then finish up the upgrade of my Soft-Pointing-Tool. Then I can think about move forward to trying to prove this Sonic-Crack-Theory.

I came up with this theory just lately while was laying on my back feeling under the weather. Now that I'm back on my feet I can make plans to finish up one project and move onto the next.

I'm afraid I've gotten back into the bad habit of posting my ideas before I've had a chance to prove them. I had stopped doing that shortly after joining this forum but, with the success I've had with the Boat-Tailed Gas-Checks idea I'm afraid I let myself drift back into this bad habit.

After this thread runs its course I won't be posting any more of my ideas, theories or inventions until I've had a chance to complete them. In any forum-setting there are just way to many dream-killers with good intentions to keep one from bringing their dreams to fruition. I thank God for those here who still have dreams of their own and encourage others who do.

In regard to the work that our fellow forum member oldpara goes; I've been following his post since he started the thread in question. He has some awesome creations. I love that kind of stuff. I absolutely love it. I've always been drawn toward creative people but, in my own case and with my own ideas, I prefer to do all my own work. This way any failures I encounter are my own and any successes I achieve are my own; otherwise it's to easy to blame others for one's failures and to easy for others to steal your successes.

Artful: I don't think I've ever mentioned to you how grateful I am for your inputs on this and some of my threads throughout this forum. I may be way off base with my interpretations of the number of hits that some of my other project-threads have gotten over time but, I'm thinking there are thousands of lurkers on these threads that never say a word one way or the other. Then there are those who chime in with their well meaning cliches only to tell me why they think my ideas won't work. And then there's yourself and a handful of others that will post replies of encouragement. Many thanks for the offers to help.

Right now I have my hands full with the projects I'm working on now. If any of you want to help, here's how you can help me. Next time you say your prayers, mention me and this project. I'm kind of wanting to see it succeed.

HollowPoint

[Artful]

Ok, we'll leave it in your hands - glad your feeling better - one suggestion look into super sonic propeller driven plane history.

[jmorris]

As you already have the solid drawing, any chance that you could just get someone to 3D print your prototypes?

[HollowPoint]

Ok, we'll leave it in your hands - glad your feeling better - one suggestion look into super sonic propeller driven plane history.


The small amount of information on "Propellers" (not Impellers) that I came across seemed to indicate that a "Propeller-Type" of configuration would become limited by the Propeller itself.

In the old WWII aircraft for example, the air speed of these craft would only allow then to travel up to a certain speed before the propeller started hindering the flight characteristics of the plane. I can't remember exactly what that air speed was but, this is the reason I opted for the "Impeller" configuration as apposed to the "Propeller" configuration. Both will suck volumes of air and create forward momentum but in my estimation, the "Impeller" configuration does so with less resistance.

Even so, I'll check into your suggestion a little more.

It is possible to have prototypes 3D printed. Both in the plastic medium that the lower end printers put out and in "Sintered" metal 3D printing. The "Sintered" metal printing would be out of the realm for me because It's to expensive; especially if more than one prototype is needed.

The plastic medium 3D printing wouldn't be so bad but, I have the lathe and mill to make up these prototype so why pay the additional expense of 3D printing them?

I'm doing it on the cheap. It's a basically a million-dollar idea with a fifty-dollar R and D budget. (optimistic I guess)

HollowPoint

[opos]

Non engineers have solved lots of the worlds mysteries and needs...I for example devised a disposable handkerchief many years ago...didn't pursue it and someone did...it's called Kleenex.

Whatever comes of the whole thing...I like the CAD design drawing

[HollowPoint]

opos:

Thanks for the kind word.

I'm tickled that the drawing came out as clear as it did. I used the Solidworks software to draw it up. I'm self-taught so my drawings don't always come out as I'd like.

I've mentioned this before in some of my other post and topics. When you're self-taught, you have a teacher that's just as ignorant as the student. It's a hit or miss affair.

HollowPoint

[Artful]

The small amount of information on "Propellers" (not Impellers) that I came across seemed to indicate that a "Propeller-Type" of configuration would become limited by the Propeller itself.

Actually a lot of WW2 aircraft reached and or passed into supersonic flight speeds in a dive - the problem was the aircraft frame/controls wasn't designed for it. Plenty of stories out there say Yeager wasn't the first. There are certainly many pilots who approached the sound barrier but didn't live to tell about it. Controls frozen or unresponsive - plane screaming toward the ground - P51, P47, P38's were all fast enough probably ME262 as well.

In the old WWII aircraft for example, the air speed of these craft would only allow then to travel up to a certain speed before the propeller started hindering the flight characteristics of the plane. I can't remember exactly what that air speed was but, this is the reason I opted for the "Impeller" configuration as apposed to the "Propeller" configuration. Both will suck volumes of air and create forward momentum but in my estimation, the "Impeller" configuration does so with less resistance.

Even so, I'll check into your suggestion a little more.

HollowPoint
The thing about being self taught is there is no lesson plan, which slows the learning process - but it also allows side trips to things outside a traditional course of education. At one point I thought I had a unique idea for a suppressor baffle design - turns out it was a reinvention - I have one now made by someone else and it works well for what it is, not the quietest but the quietest for it's size.
Let me spark your fertile mind
http://www.heliciel.com/en/logiciel-calcul-helice-aile/optimisation%20vitesse%20rotation%20nombre%20pales %20helice.htm
http://www.heliciel.com/en/images/helice%20contra%20rotative%20snecma.jpg

http://en.wikipedia.org/wiki/Republic_XF-84H -
"Thunderscreech" was an experimental turboprop aircraft derived from the F-84F Thunderstreak.
Powered by a turbine engine that was mated to a supersonic propeller,
http://upload.wikimedia.org/wikipedia/commons/thumb/0/06/F-84H.jpg/800px-F-84H.jpg

http://www.langleyflyingschool.com/Pages/CPGS%204%20Aerodynamics%20and%20Theory%20of%20Flig ht%20Part%201.html
http://www.langleyflyingschool.com/Images/CPL%20Aerodynamics%20and%20Theory%20of%20Flight%20 Part%201/Shock%20Wave%20of%20supersonic%20flow.gif

http://history.nasa.gov/SP-4219/Chapter14.html
http://history.nasa.gov/SP-4219/4219-322.jpg
An advanced propeller swirl recovery model is shown in the NASA Lewis Research Centers 8 x 6 foot supersonic wind tunnel. Propeller efficiencies and noise are measured at cruise much numbers up to 0. 80 and at takeoff and approach conditions. Vane pitch angles and propfan-to-vane axial spacings are varied. The testing was part of the Advanced Turboprop Project, with the goal of providing the technology base to enable the U.S. development of quieter, fuel efficient turboprop engines with a comfortable aircraft interior environment. (NASA photo no. 90-H-78).

You of course don't need the entire propeller as your not using it as a driving force.

Remember Air is compressible - Liquids are not so much

The other thought is Ventura effect and ducting like the bullet I showed above. I never bought any but the hole taking air into a central chamber and allowed to exit out the back is a interesting idea - no? What if you combined the two - your prop/impeller directing towards a vent into the body to exhaust out the back?

[HollowPoint]

When we picture our own ideas in our minds we're able to see them in their perfect state. When I picture my own theory as it pertains to the bullet design I have in mind, I can see it as I want it to be, functioning as I want it to function; and it functions perfectly.

Fabricating and testing our ideas generally turns out to be anything but perfect.

It can be incredibly difficult to explain our personal views of our perfectly envisioned idea to others, especially when trying to do so with the written word.

I'm having trouble wrapping my head around the "Propeller" as a viable method for this particular application. My difficulty in understanding how a Propeller would work is due to the interior dimensions of a rifle bore.

My miniscule understanding of Propellers as a means of creating forward momentum of any kind is that the Propeller blades themselves have to have a certain amount of length in order to have the surface area to displace sufficient amounts of air to accomplish their intended task.

On an aircraft, the Propellers can be made as long and as many as needed for optimum performance because they're basically rotating in open air. On a 30 caliber bullet launched at 2700 fps, I'm picturing a Propeller being sheared off by the velocity and centrifugal force as soon as it leaves the muzzle.

To my way of thinking, Propellers are used to pull an object forward. I'm not sure exactly how to describe it so it makes sense to everyone but, the Impeller setup I'm envisioning is design to bore a bullet-sized-diameter hole through the air in front of my bullet, pulling that bit of air backward and thus mitigate or eliminate the pressure wave that would otherwise stack up in front of the bullet and eventually initiate a Sonic-Crack.

I don't know if this makes any sense or not. It's just the way I picture it in my mind.

Perhaps a Propeller setup will work as you're seeing it in your mind. I'm struggling to see it that way. Maybe you can elaborate a little more. Then it might make it easier to see it how you're see it.

HollowPoint

[Artful]

I wish I had the computer drawing skills to picture what I see in my minds viewpoint ... but alas I do not. If you look at your original drawing I'm seeing your impeller and I'm seeing the air build up in front of it. As the boolit rotates at high RPM it's trying to cut into the compressed air and move it out of the way.

I see a change in the impeller to make the bite work better in supersonic air - if you keep the vanes and use them to channel the compressed air to a vent on the body of the boolit that connects to a central cavity that has an exit to the rear you can move the compressed air out the back into the low pressure zone that forms behind a normal boolit. In the past the air force did this and several car makers do so also to improve the aerodynamic's.

In the airplane pictures, you have to understand the propellers stick out so they have a place to move the air (behind the aircraft), what I'm trying to get you to see is the supersonic propellers don't look like grandpa's propeller for sub-sonic aircraft - they have a different shape to try and keep turbulence from forming and making more drag. I don't see a boolit with prop sticking out :oops:

Even if you just took a regular J-word bullet - drilled a central cavity from the back and then cut smaller holes in such a way as to help scoop the air into the cavity and exhausted out the rear (much as the Italian design) it might make a difference - I don't know.

http://images.gizmag.com/hero/compbullets.jpg

I'd ditch the holes around the mid-section and move the remaining ones further up the ogive and angle them to help pull air in.

[popper]

Sorry, it's not the burble that causes the boom. It's the >1000x pressure cone that your ear detects. Note the primary wave and secondary waves in the pic. If you can cause the waves to make an interference pattern, you can reduce the boom. If you make the interference pattern 'move' you can mask the identifiable noise.

[Artful]

He wants to change the low pressure zone in the back - which depending upon how it's done could reduce the pressure cone produced and make it quieter. NASA proved it is possible to change the signature of the sonic boom with their modified aircraft - He just wants to take a new approach to it.

[M-Tecs]

I'm not sure but I think that you're not taking into account the ultra-high RPM's that the rifling will impart on the bullet and the "Impeller" action that the fins will produce. This is why it will be critical to find the correct pitch for the "Impeller-Fins."

Try calculating the RPMs on your fastest moving cast lead projectile fired from a standard 1 in 10 twist 30 caliber barrel with the bullet moving at about 1800 fps. Then do the calculation using a 168 grain bullet traveling at about 2700 fps out of the same 1 in 10 twist barrel. Those fins are rotating far faster than the bullet is moving forward.


In both cases the bullet rotates one revolution for every ten inches of advancement. How will the fins rotate faster than the bullet moves forward?

I do understand the trig behind the high point of the fin moving faster than the point of the bullet because of the addition of the circular (angular) movement but wouldn't this create addition pressure waves?

[greywuuf]

Ever shoot a bullet into the ice? It stops going forward....and hops back on top of the ice and just spins.....fairly easy to spin faster than you are moving forward.

[greywuuf]

Another example is a general aviation aircraft with the brakes on....doing a run up......the prof is spinning pretty fast but not going forward....static thrust is measured that way.....with enough horsepower you cavitate....

[M-Tecs]

Neither example apply to the OP statement. It’s still one revolution for every ten inches of bullet advancement. When you fire a supersonic bullet the rate of forward advancement decreases way faster than the rpms decrease. At the muzzle the bullet rotates one revolution for every ten inches of advancement but at 1,000 yards the rotation is probably closer to one revolution for every three or four inches of advancement. The reality is that the sonic boom from a bullet at 200 yard and 1,000 yards sound the same. If you doubt this spend some time in the pits at high power matches were you have bullets going a couple of feet over your head at 200, 300, 600 and 1,000 yards. I have been in the pits at 500, 800 and 900 yards and the sonic boom appears to be the same also.

[HollowPoint]

Yea; I'm beginning to regret ever posting this Sonic-Crack-Theory before I made any attempts at proving or disproving it.

The image I posted served its purpose, which was to give the readers a visual idea of what I was getting at but, some folks seem to be stuck on that image as it's pictured and unable to see beyond it.

Regardless of wether it's one-in-ten revolutions or one-in-whatever revolutions, it's the angle of the fins in addition to several other factors that will determine the effectiveness of my theoretical Impeller-Setup. What appears to be happening here is that some are choosing just one of the many components of this theory and determining it to be a failure from that one component or that one perspective alone.

Please remember, this theory is brought in from outside the proverbial "Box." Up to now, most -if not all- replies to the contrary have their roots inside the proverbial "Box". That tends to make one perspective correct when viewed from inside that "Box," and frustrating when viewed from outside that same "Box." I'm on the outside looking in and you're on the inside looking out.

Close your left eye and with your right eye, fix your gaze on any object in front of you. Now close your right eye and look at the same object with your left eye. You're looking at the same thing but, you're now seeing it from a slightly different angle. That slight difference in angle can make all the difference in the world.

You'll hear no more from me on this topic until I've started this project. This thread should be dead soon soon. When I've finished my present projects I'll resurrect this thread to let you know that I've started work on this Sonic-Crack theory. Until then you are free to hash it out amongst yourselves.

HollowPoint

[M-Tecs]

it's the angle of the fins in addition to several other factors that will determine the effectiveness of my theoretical Impeller-Setup. What appears to be happening here is that some are choosing just one of the many components of this theory and determining it to be a failure from that one component or that one perspective alone. HollowPoint

The laws of physics are relatively inflexible. To date every item in the atmosphere moving faster than the spend of sound has created a sonic boom. Please help us understand what the several other factors are that will allow you to change the laws of physics.

It was suggested earlier that you look at propellers. That is the closest model to what your impeller bullet model is. On the high speed prop aircraft the aircraft itself does not break the speed of sound but the prop tips in some cases do. This also happens with helicopters when the rotor tips break the speed of sound.

Larger items traveling faster than the speed of sound make a louder sonic boom than a smaller items so that would suggest that mitigating the sonic signature is possible.

Whether it’s a bullet, a prop tip, a loop on a bull whip or your impeller tip the laws of physics suggest it will create a pressure wave once the speed of sound it achieved either in a forward or a rotational velocity. What am I missing?

[popper]

I think the only way to get a partial solution is to make a fluted ogive. Kind of like the phillips boolit. Stay with me here. You will get a pressure ridge off the nose and off the flutes. Imagine umbrella spines as the pressure ridge, doubled and rotating. To the listener, it pulsates and would be longer - time-wise. Same principle a muffler or suppressor uses, but you can't get the ridge to point forward on a boolit. May turn a crack or boom into a thud. 'Super-sonic' prop blades have to be short to keep the tip speed down and sub/super modes down to prevent the blade from coming apart. Light flies on my fly rod will give that 'crack' and usually break the leader.

[salty dog]

Something of an explanation about supersonic propellers: The only thing going supersonic are the tips of the propeller blades. The plane itself never went supersonic. Which brings me to what I wanted to point out. I too am a bit skeptical that you are trying to push something through the air without disturbing it. While it's an admirable goal, and you could be quite famous and wealthy if you succeed, I'm afraid you've bitten off more than is chewable. But anyway, since your bullet is going supersonic, it seems to me a closer analogy in the aircraft world would be a jet engine in a plane traveling faster than the speed of sound. Not a perfect analogy because the actual power comes from the jet and, most importantly, the air going in to the compressor must be slowed down to subsonic speeds before it hits the blades, but at least a jet engine is successful in moving air through the middle of an object going faster than sound.

That little bit is all I had to offer, good luck and please report your results.

[jmorris]

Ever shoot a bullet into the ice? It stops going forward....and hops back on top of the ice and just spins.....fairly easy to spin faster than you are moving forward.

Oh great, now I am going to have to go on vacation somewhere to see this. I think it might have been cold enough in Texas once in my life time for the ponds around here to freeze up enough to stop even a .22.

[M-Tecs]

No vacation needed when you have youtube

http://www.youtube.com/watch?v=zHrBm8C3WEE

http://www.youtube.com/watch?v=foZlciP6gUQ

[leeggen]

Say everyone if Hollowpoint wanted to design say a bullet that shot the same at 500ft/sec as it does at say 4000 ft/sec how many would help him in that endevour instead of telling him that the mathamatics say you can't do it. Look at how the bullet lube has come along cause some of you just didn't listen to the nay sayers and pushed ahead. I think he needs some good support cause even if at first he doesn't succeed, he may just do it in the future. Lets face it a man jumped from atmos. limits and broke the barrier and there was not a sonic boom to be heard.
Go for it hollowpoint and good luck. I've been there and proved 10 engineers wrong about producing .001 dia. carbide drills with flutes and releifs also pointed with releifs.
CD

[birch]

I think the impeller design would destabalize the bullet and actually increase the sonic boom. There would be no way to get rid of yaw which would lead to a greater high pressure cavity on one side of the bullet or the other. The surface area on the leading edge of the bullet would have no choice but to get larger.

Think of a powerful electric motor in your hand. When juice is put to the motor, it wants to twist out of your hands until the armature gets up to near neutral acceleration. The bullet would never reach a static state and would always be forced to overcome gravity, atmospheric pressure, and declining potential energy. There would be a torque curve due to the bullets rotation and increased suface area of the flutes (fins). The bullet would yaw and surface area would increase no matter how the fins were designed.

[Garyshome]

Hey let me know when you fellas get it figured out!

[HollowPoint]

This will be a while down the road. I still have about four other projects ahead of this one; and with me, there's no telling if an even more interesting project might appear on top of the four projects I'm working now.

I will get to it in the future though. When that happens I'll resurrect this thread to give you all an update.

"I think the impeller design would destabilize the bullet and actually increase the sonic boom. There would be no way to get rid of yaw which would lead to a greater high pressure cavity on one side of the bullet or the other. The surface area on the leading edge of the bullet would have no choice but to get larger. "

You make a valid point but, your point is based on the known dynamics of conventional bullets. Remember, we're working outside the box here. Your "Electric Motor" analogy is a good one. With conventional bullets this is an accurate analogy.

Picture this in your mind's-eye; a sheet of paper laying on a flat surface. Now wave your hand over the top of it and that sheet of paper wants to rise up off the flat surface. What you've basically done by waving your hand over the top of it is wipe away the gravity that held in place where it lay. (for lack of a better description) Your Electric Motor analogy only shows spin drift of a static spinning object. It doesn't take into consideration the super-sonic forward momentum of that same static spinning object for the majority of it's time of flight.

In my mind, the combination of the super-sonic forward momentum of my bullet through the air in front of it and the impeller-fins on the bullet spinning at many times the FPS of the bullet, boring a hole through the air in front of it will combine to negate the effects you've eluded to.

That forward momentum is the equivalent of the "Hand Wave" over the sheet of paper laying on a flat surface. It serves as the catalyst that wipes away or mitigates yaw or spin drift, as well as the sonic-crack that this thread centers on.

I guess I'll just have to wait to find out if it will work as I picture it in my mind.

HollowPoint

[Bren R.]

Picture this in your mind's-eye; a sheet of paper laying on a flat surface. Now wave your hand over the top of it and that sheet of paper wants to rise up off the flat surface. What you've basically done by waving your hand over the top of it is wipe away the gravity that held in place where it lay.

Actually, what you've done is created a lesser air pressure area above the paper, the same way air moving faster over the curved (and thus longer) upper surface of a wing creates lift.

Faster moving air creates lesser air pressure, and things move from greater air pressure to lesser.

That's why on the highway, when you fart in the car, it's sucked out easily by just cracking the window... whereas at a red light, you and your passengers stew in it even with the windows down.

Bren R.

[HollowPoint]

Ah; the old "Farting In A Car" scenario huh?

Less pressure is a good thing as more pressure will cause deviation of trajectory. I'm sorry I don't really know alot of the engineering jargon that would help to make my "Theory" make more sense to you more technically minded guys out there. I work off of pictures in my mind.

HollowPoint

[Artful]

Ah;
the old "Farting In A Car" scenario huh?
http://cdmtribune.s3.amazonaws.com/showcards/v2/AllPhotos/183916/p183916_n17204_cc_v2_aa.jpg
...
I work off of pictures in my mind.

HollowPoint

In my mind that's know as a Freeze Frame
http://hollandsheroes.files.wordpress.com/2012/06/19388-clipart-illustration-of-a-furious-yellow-smiley-face-with-flushed-cheeks-blowing-smoke-out-of-the-ears-and-screaming.jpg

[Bren R.]

Ah; the old "Farting In A Car" scenario huh?

Figured everyone could wrap their heads around that a little easier than the Bernouilli Principle and Continuum Mechanics.

Bren R.

[giericd]

shooting with out the sonic boom, humm "fire the laser". i like how you think out side the box but your theory wont work, here's a few reason why. no matter what design the fins are they are creating resistance, which will slow it down and create more of an airdisturbance cone on the nose as it goes through the air. you could never get it to spin fast enough to "pull" its way through the air to suck in enough air and displace it with out creating that pressure wave it's creating more. the same fins that are causing it in theory to spin are also slowing it down which is the opposite of what it needs to do for this theory to work, it needs to speed up not slow down rotation. its like trying to create a blackhole just infront of the nose of the bullet. the fins dont have an energy source to keep it spinning fast enough to pull it, the gunpowder will get it up to a specific speed which up to this point the fins would be resistance trying to slow it down, after max velocity of the round is reached it will slow down and the spin will also slow also. sonic crack can be minimized but not eliminated, and wouldn't be obtainable in shooting ever due to the nature of our fire arms. If you have a .223 going at 2500fps i'm willing to bet you would get more of a crack than something that is real thin (a few mm dia.) long and tapered on both ends at the same speed, so in modern guns we wont be shooting long thin tapered darts. you might be able to play with that pressure cone a little to form "sound cancellation". long thin tappered would obviously be best but for a gun application a projectile shaped more like a hollow tube could be played with (like a hollow slug) min thickness of the tube walls would be minimal resistance cutting through the air, length can be extended for more weight and minimal drag out the back, since air is passing through it not around it which would help with "cancellation" of the drag current out the back caused by the thin walls of the tube. but the problem with a tube would be keeping it stable to fly straight. now your design as a self defence round I like, I just wouldn't want to sit infront of a jury after popping some one with one of those things and try to convince them it was self defence! just a thought..

[Hogtamer]

what if you shot it backwards? would a rotational vortex result that offset the collapse of the shock wave? what i really want to do is put "fletching" on the back end of a Lee keydrive slug that will give me a 2" group @ 100 yds out of a smoothbore shotgun!! Live long and prosper Hollow Point...

[Artful]

So just checking - have you gotten around to a test model yet?

[Black Beard]

Simple alternative sonic theory...Sound is energy that comes from the lost kinetic energy of the bullet as it flies through the air. More energy lost in drag means more energy in noise = louder noise. To get less noise, simply pick the bullet with the best ballistic coefficient. Or look at the rate that the bullet's energy is lost in ballistic tables.BB

[Artful]

Simple alternative sonic theory...Sound is energy that comes from the lost kinetic energy of the bullet as it flies through the air. More energy lost in drag means more energy in noise = louder noise. To get less noise, simply pick the bullet with the best ballistic coefficient. Or look at the rate that the bullet's energy is lost in ballistic tables.BB

Nice theory but doesn't match data

http://img.photobucket.com/albums/v355/rowdyfisk/FAL/Hartikka_bullet_noise_graph.gif (http://smg.photobucket.com/user/rowdyfisk/media/FAL/Hartikka_bullet_noise_graph.gif.html)

[justashooter]

sonic boom is continuously generated as long as an object continues to move thru air faster than the air can be displaced, so sonic boom cannot be addressed in a single moment effort.

[Artful]

sonic boom is continuously generated as long as an object continues to move thru air faster than the air can be displaced, so sonic boom cannot be addressed in a single moment effort.

Granted you can't eliminate sonic boom that we know of but you can minimize the effect...
NASA research planes
http://www.ainonline.com/sites/default/files/styles/ain30_fullwidth_large_2x/public/uploads/2016/11/gulfstream_quiet_spike_03.jpg?itok=UtIAyHuI&timestamp=1479850294

https://img.purch.com/w/660/aHR0cDovL3d3dy5zcGFjZS5jb20vaW1hZ2VzL2kvMDAwLzAwMi 8wMDYvb3JpZ2luYWwvMDYxMDExX3F1aWV0c3Bpa2VfMDIuanBn
The long nose creates a small sonic boom with the aircraft hiding in it's shadow
https://www.nasa.gov/images/content/510438main_vsp_2k2_2400x1350.jpg
https://www.nasa.gov/sites/default/files/styles/full_width/public/thumbnails/image/16-022-supersoniccontract_0.jpg?itok=xlS-B1WJ
https://cdn.arstechnica.net/wp-content/uploads/2016/02/lowboom.jpg