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!

[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=Oubv...e_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]

AK in air with schlieren photography


NASA attempt at minimizing the sonic boom for supersonic flight
http://www.nasa.gov/vision/earth/imp..._jousting.html


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).