Cylinder Volume > Barrel Volume

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Cylinder Volume > Barrel Volume

Postby G. Dallas on Wed Jul 22, 2009 8:42 pm

The Cylinder Volume being greater than the Barrel Volume will cause the bb to be pushed through the barrel prematurely, causing a sort of "dry fire" without actually dry firing. can this problem of lack of resistance be solved by using heavier bb's?
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Re: Cylinder Volume > Barrel Volume

Postby SPC on Thu Jul 23, 2009 10:51 am

I will say I've never heard of this. But I understand it, simply it means the piston hasn't made it all the way forward before the BB leaves the barrel, causing a lack of pressure that keeps the piston safe during travel, the same pressure that is lacked from dry firing. I would say no, the BB weight would not matter, first off its extremely tiny anyways, and second, the pistons force on the air is much much much times stronger than that of the inertia of the BB, so the BB has little to no effect on the air anyways. I'm sure if you could chrono air, the FPS of air from dry firing isn't that much different from if there is a BB in front of it.

this is the info you got this from, correct? May I have a link to the site?
Barrel Suck, BS or Fact?


I’ve been looking at the whole Barrel Suck phenomenon and I just can not accept it as given.
I needed proof. So I decided to formulate some calculations as a starting point.

I’ll cover a lot more in this post, so please read through it fully before posting knee jerk reactions to my hypothesis.

For the purpose of this, I need to clarify some terms. Most will know them, but just in case…

Definitions;

aeg: automatic Electric Gun (airsoft)

Barrel Suck: The phenomenon that apparently occurs when an aeg piston begins retracting while a bbs.html'>bb is still in the barrel, causing a loss in FPS due to the piston sucking back air from the barrel behind the bbs.html'>bb.

FPS: Feet per Second – Velocity of the airsoft projectile

IPS: Inches per Second (FPS X 12) used for calculations within this hypothesis.

ROF: Cyclic rate of fire measured in Rounds per Second or RPS

My hypothesis:
Barrel Suck is a misnomer perpetrated on the Airsoft Community at large due in large part to certain active persons in forums across the world coining the buzz phrase with little more than speculation and guesswork and a great degree of “Technical Gobbs.html'>bbledegook” to fool the masses into a perpetual belief that what they say must be true.


Here are some mathematical statistics and formulas that can be duplicated to match any guns specific performance values. This is assuming the aeg is in prime operating condition and NOT double feeding due to magazine or hop-up issues.


Test Bed #1 (Long barrel, Low FPS, High ROF):

Inner Barrel Length : 600mm (600mm X 0.03937 = 23.622 in, but let’s call it 24”)

FPS: 250 (about the lowest FPS for a decent gun)

Cyclic Rate: 20 RPS

Calculations:
At 250 FPS, it takes a bbs.html'>bb 0.008 seconds to travel 2 feet (24”, or just over 600mm).
[1 second, divided by 250 feet, times 2 feet]

At 20 RPS, a bbs.html'>bb is fired once every .05 seconds.
[1 second divided by 20]

Assuming Zero Point on our timeline to be the point where the piston releases from the sector gear, the bbs.html'>bb exits the barrel at approximately 0.008 seconds, leaving 0.042 seconds before the next shot even begins to travel down the barrel.
[0.05 minus 0.008]

The bbs.html'>bb is only in the barrel for the first 16% of the firing cycle.


Test Bed #2 (Long barrel, High FPS, Moderate ROF):

Inner Barrel Length : 600mm (600mm X 0.03937 = 23.622 in, but let’s call it 24”)

FPS: 400 (the golden number for many)

Cyclic Rate: 15 RPS

Calculations:
At 400 FPS, it takes a bbs.html'>bb 0.005 seconds to travel 2 feet (24”, or just over 600mm).
[1 second, divided by 400 feet, times 2 feet]

At 15 RPS, a bbs.html'>bb is fired once every .066 seconds.
[1 second divided by 15]

At Zero Point (piston release), the bbs.html'>bb exits the barrel at approximately 0.005 seconds, leaving 0.061 seconds before the next shot even begins to travel down the barrel.
[0.066 minus 0.005]

The bbs.html'>bb is only in the barrel for the first 7.5% of the firing cycle.


Test Bed #3 (Average barrel, Average FPS, Moderate ROF):

Inner Barrel Length : 363mm (363mm X 0.03937 = 14.29 in, but let’s call it 14.5”)

FPS: 350 (pretty standard for non TM stock guns)

Cyclic Rate: 15 RPS

Calculations:
At 350 FPS, it takes a bbs.html'>bb 0.0035 seconds to travel 14.5 inches.
[1 second, divided by 4200 IPS (350 FPS X 12), times 14.5]

At 15 RPS, a bbs.html'>bb is fired once every .066 seconds.
[1 second divided by 15]

At Zero Point (piston release), the bbs.html'>bb exits the barrel at approximately 0.0035 seconds, leaving 0.0625 seconds before the next shot even begins to travel down the barrel.
[0.066 minus 0.0035]

The bbs.html'>bb is only in the barrel for the first 5.3% of the firing cycle.

Based on these examples, anywhere from 84 to 94.7% of the time (while the gears are spinning) there is nothing going down the barrel!



Also busting this “Barrel Suck” myth is the actual function of the aeg gearbox..

Before the sector gear teeth can even engage the piston teeth, the tappet plate is disengaging the nozzle from the hop-up chamber thanks to the ingenious location of the tappet nub.
While the piston is retracting, it will draw air through the nozzle, but since the nozzle is no longer sealed within the hop-up chamber, it can not suck air from the barrel. Try sucking soda through a straw with the straw opening just millimeters outside of the liquid. All you’ll get is air. Your sucking has no affect on the soda, just like the piston has no affect on the bbs.html'>bb in the barrel (if it’s even still IN the barrel).



Now, with all of that being said, there is a problem which occurs with improper cylinder sizing which will affect FPS, Accuracy, Consistency, and Performance.

This problem occurs when your cylinder does not physically have enough air volume to fully propel a projectile down the entire length of the barrel.

Typically, cylinders have venting holes at certain positions along the length of the body. This is primarily to minimize air resistance during piston acceleration after release in small to medium barrel lengths. There are many resources available to guide you to the proper cylinder type for your barrel length.

Putting a 500mm long barrel in a gun with a cylinder designed for a 363mm barrel is looking for trouble. Your cylinder will not have the sufficient air volume to propel the projectile down the entire length of the barrel.

Use the following formula:

Cylinder ID in mm X Cylinder ID in mm X 3.1415 (Pi) X Cylinder length in mm (to hole, if it has one) = Cylinder Volume in Cu mm

Barrel ID in mm (if you don’t know the ID, use 6.08) X Barrel ID in mm X 2.1415 (Pi) X Barrel Length in mm = Barrel Volume in Cu mm
If your Cylinder Volume exceeds your Barrel Volume, you’re good to go.
If it’s close, you may want to move to a Zero or Bore Up cylinder.


So, in closing, the phenomenon known as “Barrel Suck” has absolutely nothing to do with barrel suck. It is simply a result of improper sizing of cylinder type to barrel length.


The underlined to me is exactly what causes barrel suck, but he doesn't want to go into these "problems". Second, he used a lot of math and based many things on assumptions. There are many things math has not explained, and while we want to take math as concrete, it can't always, and in this case, the assumptions can easily cause human error.
In his examples he listed the time it took for the BB to leave the barrel, but he never showed how long it took for the air nozzle to move away, preventing a seal and thus a suction from lack of air. If the BB took .008 seconds to leave the barrel at 250FPS, but the air nozzle took .009, then there is a seal during the whole time the BB travels the barrel, which means a lack of air will cause a suction.

That's my input on this, I say his experiment is flawed, but the concept can be completely true.
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Re: Cylinder Volume > Barrel Volume

Postby epic skills on Thu Jul 23, 2009 3:39 pm

well it is fine if it is more but only for so much, my friend has a type 1 teflon coated cyllinder in his G36c with a 247mm barrel, and it seems to work well enough, though I may trade him the one in my JG m16(nickle plated, a bit longer port on it, not type2, but more than 1) for his, and see if that makes a difference for either of us. In my experience, it doesn't make a huge difference if you have a shorter barrel with more volume, though as long as you don't do something dumb, like sub 300mm with a no port, you should be fine.
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Re: Cylinder Volume > Barrel Volume

Postby G. Dallas on Thu Jul 23, 2009 4:39 pm

You can link that info, but you can also work on it. I did notice he didn't mention how long the air flow was in the barrel while reading it myself, but I didn't think anything of it because it had already answered my question about the barrel suck phenomenon. I consider it valuable info, and recommend linking it. I learned quite a bit from it about gearboxes. but I still recommend you make it better. (or try) lol
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~CYMA G18c AEP
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Re: Cylinder Volume > Barrel Volume

Postby SPC on Thu Jul 23, 2009 4:58 pm

actually, I want the site it was from.
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