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Discussion Starter · #1 ·
So... what do you think a BB does when it travels inside an inner barrel at low and high FPS?
Bounce chaotically? Bounce a few times? Bounce many times? Float in the middle? Float at the top? Or what?

I've gathered information from many sources and it's never consistent!
>: Quite frustrating :mad:
 

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This is just based off my knowledge of fluid dynamics. I think at lower fps the bb will bounce more beause there is not as much compressed air supporting it to make it "float" in the middle. The way I see it, once you get past a certain fps the air will try to escape faster than the bb's momentum will allow and it will surround the bb,making it "float" inside the barrel.

Or, the higher pressures from higher fps might be too unstable and too turbulent, causing the bb to go haywire.

I do know a way to test it, but it would require great skill and be costly. If you have some .3 aluminum bbs to make contacts, some machine to fabricate barrels, and some sort of ultra-flat electronic sensor, you can test it. My idea is to place hundreds of ultra-flat voltage sensor things around the inside of the barrel, somehow connect them to the computer, have feed wires from a battery connect to the barrel itself, all without being in the way of the bb. Then when the bb connects the sensor to the power you will see the spike on your computer.

Another theoretical way to test it is to have a highly sensitive accelerometer strapped tight to the barrel to feel when the bb hits a side and in what direction.

This is all just theoretical. Silent, tell me if my rant on ways to test isn't really pertinent to this and I'll delete the ways to test.
 

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Discussion Starter · #3 · (Edited)
I do know a way to test it, but it would require great skill and be costly. If you have some .3 aluminum bbs to make contacts, some machine to fabricate barrels, and some sort of ultra-flat electronic sensor, you can test it. My idea is to place hundreds of ultra-flat voltage sensor things around the inside of the barrel, somehow connect them to the computer, have feed wires from a battery connect to the barrel itself, all without being in the way of the bb. Then when the bb connects the sensor to the power you will see the spike on your computer.

Another theoretical way to test it is to have a highly sensitive accelerometer strapped tight to the barrel to feel when the bb hits a side and in what direction.

This is all just theoretical. Silent, tell me if my rant on ways to test isn't really pertinent to this and I'll delete the ways to test.
Ah those ways are valid, although I have nowhere near the capability to pull those off >:D I have a feeling there's at least one company out there that has done the testing, but for some reason the results are just dang difficult to find.

This is just based off my knowledge of fluid dynamics. I think at lower fps the bb will bounce more beause there is not as much compressed air supporting it to make it "float" in the middle. The way I see it, once you get past a certain fps the air will try to escape faster than the bb's momentum will allow and it will surround the bb,making it "float" inside the barrel.

Or, the higher pressures from higher fps might be too unstable and too turbulent, causing the bb to go haywire.
Maybe the BB can do what everyone has claimed, but it's very dependent on FPS and bore size :shrug: The most common thing that's emitted by people explaining what a BB does is the FPS and the bore size being used :doh:
 

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They also forget weight. Weight matters because the more momentum it has the more of a difference it will make to the testing.
 

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Discussion Starter · #5 ·
Yeah they don't mention that as well :D The exact words most of them use are inner barrel, bb, and air :nuts:
 

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Discussion Starter · #8 · (Edited)
I believe:

that a LRB works by giving spin to a BB after it contacts the upper ceiling of an inner barrel. After contact, the surface interaction will shoot the BB down to the bottom of the inner barrel and the BB will again rise after making contact with the floor of the inner barrel. This will look like bouncing if it were possible to look inside an inner barrel.

The backspin of a BB and it's interaction with the top of an inner barrel is spinning in a way which will actually help the BB gain more spin. Similar to how a bucking would interact with a BB that already had backspin applied-- it would add more spin :O

The majority of friction (which causes hop-up) will actually be lost when the BB touches the bottom of the inner barrel. When the BB touches the bottom of the inner barrel, it is similar to spinning a ball backward and throwing it in front of you. The ball's spin will terminate much faster because now the ball's rotation and floor are going in opposite directions.

It's my gut feeling and educated guess that a LRB increases the distance it takes for a BB to touch the bottom of a barrel once it's propelled downward by the upper ceiling (so more time away from the bottom)
and
because of the new angle of contact between the BB and the inner barrel. There are now actually different amounts of force because of these new angles of contact. Which to me would be more behind the BB when it touches the floor of the barrel and more in front of the BB when it touches the ceiling. This also means that the moment of contact with the ceiling has more friction because the contact point is now more in front of the BB and this causes more hop-up spin.

An easy way to imagine why the angle of contact is important is to visualize a ball tossed down a hill. The angle of contact after each bounce is behind the ball so it does not have much force going against it. The ball will continue to move in the opposite direction of the force applied (behind it.)

Imagine a ball being tossed up a hill. The ball's contact point is in front of the ball. A lot of force is now acting against it after each subsequent bounce and eventually the force will not allow the BB to bounce upward anymore.

Now if you were to increase the angle of contact even more, you eventually end up with a wall. Tossing a ball against a wall will have a lot of opposite force acting upon and you know what happens :yup:.

The increased force in front of a BB is actually why a hop-up protrusion gives more spin. When hop-up is adjusted a little bit, the rubber is touching more towards the top center of a BB. When the hop-up is adjusted more, the rubber gets in the way and touches more of the top front of the BB. Most people believe it is because the rubber is pressing HARDER on the BB, but it's actually more about the angle at which the BB is being given its spin.

Of course in these analogies, I do not mention gravity, but in a vacuum less space, the same concepts hold true.

In the end, I believe it is okay to speculate what may or may not be the truth. Until better and more reliable research tests are performed, nothing is certain. The bad thing about Airsoft is there's more guessing than testing lol. I just know there must be data somewhere out there, but where to look! ARGH!!~
 
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Discussion Starter · #10 ·

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What does a BB do in a barrel? - It travels down it :p

When A bb is engaged in the hop up and just waiting for the air blast behind it would it not bounce from accelerating so fast and contacting the nub on the rubber so suddenly. Surely that would make it bounce down the barrel.

An LRB may work because you've simply eliminated this and with the curve in the barrel you are forcing the air out at different ratios (?) under and on top of the bb thus making it 'ride up' in whatever direction the curve is going?

I don't know, just a half assed-guess from someone who is bored.
 

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Discussion Starter · #13 ·
What does a BB do in a barrel? - It travels down it :p

When A bb is engaged in the hop up and just waiting for the air blast behind it would it not bounce from accelerating so fast and contacting the nub on the rubber so suddenly. Surely that would make it bounce down the barrel.

An LRB may work because you've simply eliminated this and with the curve in the barrel you are forcing the air out at different ratios (?) under and on top of the bb thus making it 'ride up' in whatever direction the curve is going?

I don't know, just a half assed-guess from someone who is bored.
It makes sense :) Nobody can be proven wrong right now lol. Any guess is as good as any other >:D. I just don't understand how they (being companies like Redwolf) have concluded that there is an air cushion effect.

Directly from the RWA website:
http://redwolfairsoft.com/redwolf/airsoft/BulletDetail?bulletID=91
A BB travels down an inner barrel on a cushion of air so it does not touch the sides. This slight give also means the BB can move side to side inside the barrel, not much, but just enough to allow those BBs to come out of your barrel in a cone pattern instead of a line. A tighter barrel means less space which means less wobble which means a tighter cone. A longer barrel means more time for the BB to stabilize its wobble which again means a tighter cone.
They never mention if this was concluded from physics logic (basically educated guesses), empirical testing, nor did they mention any factors involved such as FPS.
As far as their statement goes, the air cushion works for any FPS and any condition :nuts:. I'm still not a believer unfortunately.
 

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Okay. After doing some reading, I have found that (according to my research) the most likely explanation for what bbs do inside the barrel is:

A regular hop mound will apply a downward force as well as a backspin upon the bb, causing it to be forced to the bottom of the barrel and bounce along the barrel, until such a time as when the Magnus effect will take over from the reaction force of the top of the barrel, and allowing the bb to slide along the top. This would suggest, that when using a normal hop, a long barrel with a larger bore would be beneficial. Obviously, don't overvolume.

With an R-hop or some variant thereof, it would seem as though the bb is not forced down, rather the spin, because it is imparted over time, allows the magnus effect to hold the bb against the top of the barrel right away, which actually imparts more spin, if you think about it. This allows the bb to make small bounces along the top of the barrel, but never contact the bottom of the barrel unless a very tight bore is used. Later on, the bb will simply ride the top of the bore to the end of the barrel. This would suggest that a shorter barrel could be used, but again, that a normally-sized bore should be used - due to the fluid mechanics of the bb traveling down the barrel, a tighter bore will force the bb against the top of the barrel, stabilizing the spin much like an LRB.

R-hop and LRB will do much the same as above, but due to the bend in the barrel, the bb will stabilize against the top of the bore much more quickly, and will actually be able to gain some topspin from the top of the bore. This suggests a slightly longer barrel, again, should be used, and (I actually did the math here) that a bore diameter of 6.0347 is optimal to force the bb to the top of the bore and keep it there. This number will change as you change the μ of the bore (steel or brass) but it always ranges from 6.03321 (steel) to 6.0352 (brass). I put 6.0347 because it produced the most consistent output.
 

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Discussion Starter · #15 ·
This allows the bb to make small bounces along the top of the barrel, but never contact the bottom of the barrel unless a very tight bore is used. Later on, the bb will simply ride the top of the bore to the end of the barrel.
output.
This is probably possible at certain FPS ratings and with the right combination of BB parameters, but I think it's quite difficult to determine because this is all assuming The Magnus Effect is a key factor, if not THE key factor, inside of the barrel.

Personally though I believe the BB may still bounce at the bottom. I'm going to crunch numbers when I have enough free time so I can at least mathematically present my logic... I may be wrong after I run some numbers, but who knows? >:D :D I do agree with most of what you said.
 

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Exactly. I assumed that the spheres have a perfectly smooth surface, and if they don't, then (probably) a more important factor is going to be the static friction between the bb and the air, not necessarily the magnus effect.

I used the Magnus effect because it is easy to calculate for, and the factors it addresses are easy to adjust and measure.
 

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Discussion Starter · #17 · (Edited)
Other effects (and obviously not all >:D) to consider is the drag force, buoyancy, and frictional forces. Frictional forces in my opinion are the most difficult to calculate so I'm primarily going to focus on the aerodynamics :yup:.

I'm not an aerodynamics engineer, but I think the Magnus Effect is made to counter-act gravity and will exhibit lift if the airflow around and behind said object is more steady than turbulent. The pressures inside an inner barrel may be too high and capricious so I'll have to look into that.
 

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Discussion Starter · #19 ·
It's not a force, it's an effect. Just be careful of that one, and you'll be fine. ;)

Personally, I find that friction is not too bad, but buoyancy is a royal PITA if you don't have a nice calculator. Due to the curl operator definition, doing that out by hand gets really nasty really fast.
Thanks for the correction. My mind slips sometimes. That's why I tend to edit my posts a lot :lmao:.
 
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