❓ Acoustics Question: Projectile Flight Noise 𐃘 How to keep it down?

[6gun]

yes but at least they were not purposely aiming at you..umm with im assuming AK 47 and full auto burst .. yes let's disappear into the woods..
Mark

No, I meant I feel your pain exactly . Got shot at by somebody on horseback with a rifle, I was on a motorcycle with permission for those trails from the owner. That sorta thing. The ak incident for me was very different, but scary. Glad you're OK too.

 

[6gun]

@markhooper Gyroscopically stable = stabilized by spinning. This refers to slugs.

Pellets are stabilized by drag as air moves across and around the pellet’s skirt.

This is my understanding.

And a small amount of twist. You're correct with my understanding of a stabilizing shape too.

 

[lbc_PSI]

Probably similar to high drag arrow fletching. Low profile low offset plastic vanes were much quieter than feathers of any size. The vane made a slight whooshing noise.while the feathers sounded like a V2 buzz bomb. You could hear the feathers coming way before the arrow hit the target..like as soon as they left the string.

Now I’m going to have to stand down range to hear pellets vs slugs for myself..safely, of course.

 

[Ezana4CE]

Probably similar to high drag arrow fletching. Low profile low offset plastic vanes were much quieter than feathers of any size. The vane made a slight whooshing noise.while the feathers sounded like a V2 buzz bomb. You could hear the feathers coming way before the arrow hit the target..like as soon as they left the string.

Now I’m going to have to stand down range to hear pellets vs slugs for myself..safely, of course.

Interesting.

 

[markhooper]

@markhooper Gyroscopically stable = stabilized by spinning. This refers to slugs.

Pellets are stabilized by drag as air moves across and around the pellet’s skirt.

This is my understanding.

thank you, it's more than I know.
always good to learn something.
Mark

 

[markhooper]

No, I meant I feel your pain exactly . Got shot at by somebody on horseback with a rifle, I was on a motorcycle with permission for those trails from the owner. That sorta thing. The ak incident for me was very different, but scary. Glad you're OK too.

I'm sure military guys get that a lot, and are very fortunate to come home, we should all be thankful for their service..
but is civilians? getting shot at on purpose is one bad thing.. AK 47 full auto is another..
to be honest I started packing a 45 Ruger old army black powder.. figured one round in their direction might get them behind cover instead of shooting but more importantly if have plenty of smoke cover to vanish into the woods, not sure dates but it's possible I had my baby girl with me.. now that's fighting matter if it was.. but I don't remember..
Mark

 

[JungleShooter]

Just now reading — had a full Sunday, like always.

Thanks for all your attempts to get to the bottom of this.
It is intringuing, that's for sure.


Mark, I'm sorry you've had some health issues!

Dave and you all, thanks for your concern about safety.... — we've got some dividing walls in place.


So, my guesstimates are as good as yours (or a bit worse, since I failed physics in school at least once ):
➠ I might achieve less flight noise with:
⭓ lower velocity
⭓ smaller caliber
⭓ slugs (rather than waisted pellets)


Still need an accustics engineer to respond to this thread — or I need to get out there and do some test shooting. Any volunteers for the listening post...? Any?!?

Matthias

 

[dgeesaman]

@markhooper Gyroscopically stable = stabilized by spinning. This refers to slugs.

Pellets are stabilized by drag as air moves across and around the pellet’s skirt.

This is my understanding.

Pellets are stabilized by air moving over the skirt but those particular aerodynamic forces are not technically drag. Drag has a specific definition in aerodynamics that drag is the part that does not stabilize.

 

[Ezana4CE]

Just now reading — had a full Sunday, like always.

Thanks for all your attempts to get to the bottom of this.
It is intringuing, that's for sure.


Mark, I'm sorry you've had some health issues!

Dave and you all, thanks for your concern about safety.... — we've got some dividing walls in place.


So, my guesstimates are as good as yours (or a bit worse, since I failed physics in school at least once ):
➠ I might achieve less flight noise with:
⭓ lower velocity
⭓ smaller caliber
⭓ slugs (rather than waisted pellets)


Still need an accustics engineer to respond to this thread — or I need to get out there and do some test shooting. Any volunteers for the listening post...? Any?!?

Matthias

@JungleShooter It’s not so much the safety that concerns me. I’m assuming that this occurred outside of the United States and that all present consciously chose to be there. At the ranges I’ve been to people are required to wear hearing protection. The only one I can recall there being partitions in were at an indoor range, but the partitions only divided the areas where people stood or sat shooting from. They didn’t extend down range. I’m trying to envision how the range is setup.

In your scenario, are people using hearing protection? Does the wall extend all the way down the shooting lane? What’s the wall made out of? Were they wearing hearing protection?Can you describe the sound that they claim your projectiles made? You used the term “wizzing.” Does that sound ike anything many people might be familiar with? A mosquito or gnat close to your ear perhaps? Are they sure they were hearing your projectiles and not someone else’s or something else? Do you recall which projectile(s) and air gun(s) you shot on those days? How about your tune or the projectile velocity? How far away from the flight path of the projectiles were the people?

 

[6gun]

Just now reading — had a full Sunday, like always.

Thanks for all your attempts to get to the bottom of this.
It is intringuing, that's for sure.


Mark, I'm sorry you've had some health issues!

Dave and you all, thanks for your concern about safety.... — we've got some dividing walls in place.


So, my guesstimates are as good as yours (or a bit worse, since I failed physics in school at least once ):
➠ I might achieve less flight noise with:
⭓ lower velocity
⭓ smaller caliber
⭓ slugs (rather than waisted pellets)


Still need an accustics engineer to respond to this thread — or I need to get out there and do some test shooting. Any volunteers for the listening post...? Any?!?

Matthias

I think anything that disturbs the airflow or maybe even laminar flow around the projectile could make the whipping noise I had to avoid. I just turned my gun down to 3 figure velocity. Big hollow points, diabolo shapes, and flat bases inducing a vacuum behind the projectile could be places (in my mind) to avoid and see what makes the most sound. The whip sound of pellets doesn't work for me for urban stuff so I had to slow down to 850 and that's still questionable on sound. Slugs are quieter but they just keep sailing which is a problem for some of my spots too.

In the end, I stopped worrying about projectile flight noise and worried about trying to achieve maximum precision. My guns have to be 007 quiet, and I take my sketchy shots from cover so the neighbors are just wondering where the meteorite that blew up the pigeon came from.

Our neighborhood has a lot of pigeons making their home in people's solar panels. The softies want the pigeons gone but don't want to see them die or be judged for asking somebody to shoot them. Soooooo my job is basically suburban mercinary Chris Kyle work on pigeons and skunks. And 1 coyote I'm learning the patterns of. Movie quiet guns, power and calibers for most scenarios, precision to not miss. That's my mo and I think I might be doing some of the "sketchiest" pest control on the board as of right now.

No property damage sustained either.

 

[JungleShooter]

Dave,

lots of good questions — to which answers are hard to give: I should really have kept track of what were were shooting that day, and the specifics when the flight noise was present.


I think I will need to simply do a sound test:
● I will use human ears (that are younger than mine to make sure I don't miss anything).
● I will use the guns, ammo, and power setting that require stealth.
Then we'll see what I get!


➠ If there is flight noise, I will take the advice on this thread and apply it to find a solution to reduce or even eliminate the flight noise.


Thank you all!!

Matthias

 

[Ballisticboy]

@markhooper Gyroscopically stable = stabilized by spinning. This refers to slugs.

Pellets are stabilized by drag as air moves across and around the pellet’s skirt.

This is my understanding.

No they are not, please read this. https://www.airgunnation.com/threads/aerodynamic-stability-of-pellets.1276895/

 

[Ballisticboy]

Basically, it is down to how much the air is disturbed. Pellets have a more complex shape than slugs, involving the air getting around more changes in direction, so you would expect them to generally be more noisy. However, hollow points are going to generate some noise, so large hollow point slugs could also be noisy. As both slugs and pellets have rifling marks, I cannot see this as being a major difference between them. Pellets such as the JSB Hades can be expected to produce more noise, or anything which has cuts or marks on the nose to disturb the airflow.

As for reducing the noise, smooth boat tailed slugs with no meplat on the nose fired at relatively low speeds are probably as low as you are likely to get. An accurate round is likely to be less noisy than a round which is yawing, which will itself disturb the airflow. As for .177 being quieter than larger calibres, this may be true, but if the airflow remains laminar along the entire length there will be more base drag and turbulence which may cause a problem. It will all be down to the individual designs.

 

[Ezana4CE]

No they are not, please read this. https://www.airgunnation.com/threads/aerodynamic-stability-of-pellets.1276895/

@Ballisticboy Thanks for the link to detailed information. I'll take some time to read it. I'm hoping it isn't too dense to follow.

 

[Ezana4CE]

Dave,

lots of good questions — to which answers are hard to give: I should really have kept track of what were were shooting that day, and the specifics when the flight noise was present.


I think I will need to simply do a sound test:
● I will use human ears (that are younger than mine to make sure I don't miss anything).
● I will use the guns, ammo, and power setting that require stealth.
Then we'll see what I get!


➠ If there is flight noise, I will take the advice on this thread and apply it to find a solution to reduce or even eliminate the flight noise.


Thank you all!!

Matthias

@JungleShooter I’m pretty lost on this thread. I can’t recall hearing a projectile in flight aside from a ricochet. I hope I don’t ever hear one. I’m curious as to how close one would need to be to hear them and what‘s the closest common sound(s) that people with no concept can associate the sound(s) with. Are they loud?

 

[6gun]

@JungleShooter I’m pretty lost on this thread. I can’t recall hearing a projectile in flight aside from a ricochet. I hope I don’t ever hear one. I’m curious as to how close one would need to be to hear them and what‘s the closest common sound(s) that people with no concept can associate the sound(s) with. Are they loud?

Think of swinging a thin stick or switch at high speed. That sound.

 

[beerthief]

Some kids were shooting .22LR and missed the backstop ( since rebuilt 4x larger ) but the .22 flew past me and yes whizzing is a good descriptive word . i had the impression it was maybe 6 feet above my head and somewhere to my left .

 

[markhooper]

@JungleShooter I’m pretty lost on this thread. I can’t recall hearing a projectile in flight aside from a ricochet. I hope I don’t ever hear one. I’m curious as to how close one would need to be to hear them and what‘s the closest common sound(s) that people with no concept can associate the sound(s) with. Are they loud?

I can only speak from experience.. I hope you never hear one either..I honestly don't know how close they have to get but AK 47 rounds make a whistle noise back when I could hear.. as to how close,I don't know.. and I am just glad if they were very close that I heard them because otherwise I might have felt them..
actually love hearing ricochet.. off my steels out in the woods in my back yard where there's no way they can bother anything.
Mark

 

[JungleShooter]

Basically, it is down to how much the air is disturbed. Pellets have a more complex shape than slugs, involving the air getting around more changes in direction, so you would expect them to generally be more noisy. However, hollow points are going to generate some noise, so large hollow point slugs could also be noisy. As both slugs and pellets have rifling marks, I cannot see this as being a major difference between them. Pellets such as the JSB Hades can be expected to produce more noise, or anything which has cuts or marks on the nose to disturb the airflow.

As for reducing the noise, smooth boat tailed slugs with no meplat on the nose fired at relatively low speeds are probably as low as you are likely to get. An accurate round is likely to be less noisy than a round which is yawing, which will itself disturb the airflow. As for .177 being quieter than larger calibres, this may be true, but if the airflow remains laminar along the entire length there will be more base drag and turbulence which may cause a problem. It will all be down to the individual designs.

Miles,

I really had hoped you would chime in!
I have a lot of conjectures and uneducated guesses.
The voice of a pro is great to have around!


One of my need-to-be quiet shooting scenarios would be with the Altaros Smooth slugs.
.25cal
49.50gr
850fps MV (=79FPE)
domed slug
no hollow point


Applying your post to this, it might be one of the quieter setups.


Matthias