Airgun Theory Bb myth

[Nordic Norm]

Hi folks. Bbs are a loose fit in the barrel. They will literally fall out by gravity if it weren't for the magnetic probe in rifles. So how is it they are accurate? It is common belief that bbs will bounce down the bore eventually damaging it. I don't believe this bouncing theory. For one, the accuracy would be terrible. More importantly, if one looks at aerodynamic theory the Bartolli effect (if I remember the title correctly) will keep the bb flaoting centered in the boar. The bb doesn't contact the boar. High pressure air leaking around the bb will keep it centered as explained in aerodynamic theory. As the bb shifts off center, the increased volume on one side causes pressure to drop, on the opposite side the volume decreases and the pressure increases. This effect instantly and continuously corrects minute errors in the bbs flight thru the barrel. This is also how airplanes and helicopters fly. It would be difficult to observe bbs coming down the barrel. Probably dangerous also. What do you folks think? Am I missing something?

 

[hameditor]

Norm, thanks for raising a very interesting topic. My interest is in the interface between theory and practical performance. That's why HAM specializes in measuring things as much, as consistently and as precisely as we can.

So I would appreciate your comments on the results of practical accuracy and manufacturing consistency of BBs that are published here:

What Is The Most Accurate Airgun BB? The Big HAM BB Test

So, what's the answer to that question what is the most accurate airgun BB? HAM tests say that ASG Blaster BBs have clearly scored the best.

hardairmagazine.com

The Big HAM BB Test Part Two - Airgun BB Consistency

In this second part of the Big HAM BB Test, we're looking at airgun BB consistency. That's consistency of the BBs size and weight.

hardairmagazine.com

 

[Nordic Norm]

Norm, thanks for raising a very interesting topic. My interest is in the interface between theory and practical performance. That's why HAM specializes in measuring things as much, as consistently and as precisely as we can.

So I would appreciate your comments on the results of practical accuracy and manufacturing consistency of BBs that are published here:

What Is The Most Accurate Airgun BB? The Big HAM BB Test

So, what's the answer to that question what is the most accurate airgun BB? HAM tests say that ASG Blaster BBs have clearly scored the best.

hardairmagazine.com

The Big HAM BB Test Part Two - Airgun BB Consistency

In this second part of the Big HAM BB Test, we're looking at airgun BB consistency. That's consistency of the BBs size and weight.

hardairmagazine.com

It would follow aerodynamic theory that roundness matters most. The less spherical a bb the more aerodynamic correction oscillation is induced. It would be difficult to examine bbs for sphericalness (may be a new word). Probably require an expensive machine

 

[hameditor]

It would follow aerodynamic theory that roundness matters most. The less spherical a bb the more aerodynamic correction oscillation is induced. It would be difficult to examine bbs for sphericalness (may be a new word). Probably require an expensive machine

Agreed - that's why we don't do that. But maybe there's something about the ASG Blaster manufacturing process that gives improved sphericity? That could be another new word...

 

[Pumacarl]

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Interesting topic. The glass syringes video link above talks about this same thing.

 

[Miles_M]

Hi folks. Bbs are a loose fit in the barrel. They will literally fall out by gravity if it weren't for the magnetic probe in rifles. So how is it they are accurate? It is common belief that bbs will bounce down the bore eventually damaging it. I don't believe this bouncing theory. For one, the accuracy would be terrible. More importantly, if one looks at aerodynamic theory the Bartolli effect (if I remember the title correctly) will keep the bb flaoting centered in the boar. The bb doesn't contact the boar. High pressure air leaking around the bb will keep it centered as explained in aerodynamic theory. As the bb shifts off center, the increased volume on one side causes pressure to drop, on the opposite side the volume decreases and the pressure increases. This effect instantly and continuously corrects minute errors in the bbs flight thru the barrel. This is also how airplanes and helicopters fly. It would be difficult to observe bbs coming down the barrel. Probably dangerous also. What do you folks think? Am I missing something?

What you may be thinking of is the Bernoulli effect, Bartoli produced a theory on radiation pressure, nothing to do with aerodynamics. The Bernoulli effect will only really work if one side of the BB is in contact with the barrel, stopping part of the flow. As soon as there is a gap, as long as the gap is bigger than the boundary layer thickness, the suction on each side of the BB will equalize, the volume has little effect.

When the BB contacts the barrel, friction will induce spin, which will complicate matters somewhat, but may help the effect you are thinking of. None of it is instantaneous.

 

[Nordic Norm]

What you may be thinking of is the Bernoulli effect, Bartoli produced a theory on radiation pressure, nothing to do with aerodynamics. The Bernoulli effect will only really work if one side of the BB is in contact with the barrel, stopping part of the flow. As soon as there is a gap, as long as the gap is bigger than the boundary layer thickness, the suction on each side of the BB will equalize, the volume has little effect.

When the BB contacts the barrel, friction will induce spin, which will complicate matters somewhat, but may help the effect you are thinking of. None of it is instantaneous.

Thanks, I remembered the name incorrectly. The volume I refer to is the gap between the bb and bore.

 

[Nordic Norm]

If an oscilloscope was hooked up to a test barrel, then any oscillation/vibration could be measured. It wouldn't matter if the vibration comes from bb barrel contact or aerodynamic effects. If the vibration level corresponds to accuracy, ie low vibration, high accuracy, then it could be a reliable indicator of sphericalness. In addition, the magnitude of the vibration would likely indicate a looser or tighter fit. The frequency would likely indicate roundness.

 

[Nordic Norm]

The Bernoulli (thanks Miles_M) effect could be observed using a clear tube and a lightweight ball proportional to a bb fit in a barrel. Set the tube vertically, air injects into the bottom, drop in the ball and play around with it. Does the ball touch the tube? Different velocities from a balance to hundreds of fps could be observed. Horizontal testing at higher speeds could be done using a a high speed movie camera. It wouldn't be precisely the same as what is happening inside the actual bb rifle, but similarities surely would be observed

 

[pan60]

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Interesting topic. The glass syringes video link above talks about this same thing.

aplies to some of our better tool grinding fixture we use.
i think it as an air bearing effect?
not a 100%

 

[Farmplinker2]

Well, there's a reason BB guns are 5 meters and pellet guns 10 meters. It's the same one that some BB guns are 10 yard pop can and some pellet guns are 25 yard pop can guns.

 

[Nordic Norm]

Well, there's a reason BB guns are 5 meters and pellet guns 10 meters. It's the same one that some BB guns are 10 yard pop can and some pellet guns are 25 yard pop can guns.

Sometimes the bb guns are the most fun. Not shooting well today, argh, blame it on the bb gun

 

[Farmplinker2]

Sometimes the bb guns are the most fun. Not shooting well today, argh, blame it on the bb gun

And perfect for blasting pop cans, which is some of the most fun there is shooting.

 

[EdinGa]

I have quite a few smoothbore bb shooters so I don't experiment with them in my rifled barrels. This one is probably my favorite after I spent some time customizing it. 200 shots per cartridge and pretty accurate too.

 

[hameditor]

And perfect for blasting pop cans, which is some of the most fun there is shooting.

Particularly when they are full, unopened and well shaken on a hot summer day

 

[Nordic Norm]

I have a Berra 1866. It will shoot bbs very accurately with 2 pumps or more. With 1 pump bb accuracy is terrible. Pellets accuracy is great with only 1 pump. My hypothesis is, with a bb and 1 pump there isn't enough blowby air around the bb to aerodynamically float the bb in the barrel. With 2 pumps or more, the blowby air is enough to float the bb in the bore. The accuracy goes from wild bad to excellent, bb 1 pump vs 2pumps, it doesn't get progressively better with more pumps. Bbs are a loose fit in the barrel, they roll thru unimpeded. Pellets contact the barrel and are therefore unaffected by the low pressure of a single pump.
Shooting indoors, 15 ft.
What do you think?

 

[EdinGa]

Sounds plausible to me. In my experience, I see the best accuracy below 400 fps with my smoothbores.

 

[Mike Brown]

Haven't done much with bb pushers in quite a while now but have been sorely tempted by the Barra 400E...Full auto and semi auto function-410 fps with excellent accuracy and electrically driven....no co2 cartridges to buy but it is a bit over$400.....

 

[Nordic Norm]

Haven't done much with bb pushers in quite a while now but have been sorely tempted by the Barra 400E...Full auto and semi auto function-410 fps with excellent accuracy and electrically driven....no co2 cartridges to buy but it is a bit over$400.....

My Berra 1866 shoots Daisy premium grade bbs so well it isn't worth trying to load pellets in it.

 

[Florida_Man]

I've been soooo close to buying one of these. I have't shot bb's since i was 14, 43 now.

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