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Old 08-12-2018, 12:56 AM   #1
1tonne   1tonne is offline
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What Barrel Length goes with what bb weight in an AEG?

This is airsoft gold. A gift from 1Tonne to all the techs out there.

For a long time now techs in the airsoft community have been asking what the perfect barrel length is that gives the most energy for a given bb weight. Some advantages of this are that your gearbox will be under less stress as it will be easier to reach your desired fps rate with a smaller spring. So the gearbox should last longer. Since the gearbox is not working as hard, the gears and the motor are under less pressure and therefore make less squelching noise. The gearbox should also be able to cycle faster since the motor is not having to work as hard. Most of the time, the rifle should also be more accurate. The reason for this is that the quicker a bb can get to its target, the less that outside factors such as the wind will effect the trajectory. Also, since all the cylinder volume is used up, there should be less sound exiting the inner barrel as there is no extra air pushing the sound from the piston slamming into the cylinder head out of the barrel. So your gearbox should last longer, cycle fast and be quieter. Your rifle should also be more accurate and the muzzle volume will be less.


I did an experiment a while ago that answered this big question. In the experiment I used a rifle that had a full V2/V3 cylinder as I wanted to get the maximum amount of efficiency from the rifle. I also used a 550mm barrel (6.03mm diameter) and then fired every bb weight though the barrel with the bb’s trajectory traveling straight as possible. I then recorded the data. After doing this, I cut the barrel down by 10mm. Then I crowned the end of the barrel and cleaned it. I then tested the energy rates again of all the bb weights with the trajectory travelling straight and recorded them. I kept cutting the barrel down by 10mm and retesting again. Eventually, after a very long time of repeating the test, the barrel had been cut down that much that there was only a couple of millimetres sticking out of the hopup chamber.
In this experiment I chose to use an M4 rifle as it has the most common cylinder type and it seems to be the most common rifle that people use. Though I used an M4, the results should be the same for most other rifles that have the same cylinder type (full cylinder) and same style of bucking.

So here is a list of parts in the rifle for your information:
E&C M4
E&C M4 Gearbox Case
E&C 18:1 Standard Gears
E&C Full Cylinder
E&C Piston Head
SHS Piston with Full Metal Teeth(Piston and Piston head weigh 27gms)
Super Shooter M160 Spring
E&C For all other little gearbox parts
E&C M4 Standard Metal Hopup Chamber
E&C M4 Standard Bucking (About 60 durometer)
SHS High Torque Motor
SHS M4 Air Nozzle (O-ring gives better air seal)
Action Army 550mm x 6.03mm Inner Barrel
M4 Mag Well Lock/Brace (Helps to absorb shock from front of gearbox)
11.1v 2200mah Lipo

So here is what you have been waiting for. The barrel lengths that gave the most energy for each bb weight were:

BB weight Barrel Length for a 6.03mm barrel
0.2gm---------------435mm
0.23gm--------------430mm
0.25gm--------------425mm
0.28gm--------------420mm
0.30gm--------------415mm
0.32gm--------------400mm
0.36gm--------------380mm
0.40gm--------------355mm
0.43gm--------------345mm
0.45gm--------------335mm

If you have a longer nub in your packing/bucking (so R-hop), then your nub will not be protruding as far into the barrel and the bb will be able to get past easier. So you are not wasting as much air from the cylinder. In this case, you can use a slightly longer barrel. AEG’s are pretty forgiving though and so 50mm either side of these recommended barrel lengths will not really make too much of a difference. You should only lose about 0.05 of a joule.

NOTE: I have also noticed that when using a 6.01mm barrel, the barrel length can be increased by up to about 10% depending on the bb weight used. The lighter the bb, the longer you can go. This would be due to less air wastage.

Here are the specs for a full cylinder:
Diameter = 23.8mm,
Length of cylinder = 72.5mm,
Cylinder head area = 5mm,
Piston Head Area = 7mm
Compression area minus piston head and cylinder head = 60.5mm
Usable compression volume = 26915mm



BB weight-----Barrel Length-- Barrel Volume----- Ratio
0.2gm------------435mm---------12423mm3------2.17:1
0.23gm----------430mm---------12280mm3-------2.19:1
0.25gm----------425mm---------12137mm3-------2.22:1
0.28gm----------420mm---------11994mm3-------2.24:1
0.30gm----------415mm---------11851mm3-------2.27:1
0.32gm----------400mm---------11423mm3-------2.36:1
0.36gm----------380mm---------10852mm3-------2.48:1
0.40gm----------355mm---------10138mm3-------2.65:1
0.43gm----------345mm----------9852mm3-------2.73:1
0.45gm----------335mm----------9567mm3-------2.81:1

USING PORTED CYLINDERS
The advantage to these ratios is that you can now use ported cylinders and match it with the correct barrel length just by doing 3 simple calculations and then you should be able to achieve the best efficiency for your ported cylinder.

WORKING OUT CYLINDER VOLUMES ON PORTED CYLINDERS
First work out your actual compression volume of the ported cylinder. This is the entire area from the front of your port to the cylinder head. Let’s say I had a ported cylinder that was 32mm measured from the front of the cylinder, I would then minus 5mm for the cylinder head. So it would have a compression distance of 27mm. Next I need to know the radius of my cylinder. This is the diameter (23.8mm) divided by 2. Which is 11.9mm. Then we need to do a simple mathematical calculation to work out the area of the cylinder using pye x radius x radius x length.
So this is it:
3.141 x 11.9mm x 11.9mm x 27mm = 12009mm
So our cylinder volume is 12009mm

WORKING OUT THE BARREL VOLUME
Now we need to work out what the barrel volume would be by using the correct ratio from that bb weight that we will be using and the cylinder volume measurement. Let’s say I was using a 0.25gm bb, the ratio I should be using is 2.22:1. So the calculation is simply. Cylinder Volume divided by 2.22 = Barrel Volume
So this is it:
12009mm divided by 2.22 = 5409mm
So our barrel volume is 5409mm

WORKING OUT THE CORRECT BARREL LENGTH
I have already decided to use 6.03mm barrels as I like tight bore barrels more. So I know that my radius is 3.015mm. Now by using the barrel volume we need to work out how long the barrel will be. This is done with a few more small calculations.
Barrel Volume ÷ (barrel radius x barrel radius) ÷ pye = barrel length.
So, 5409mm ÷ (3.015mm x 3.015mm)÷ 3.141 = 189mm. So the best barrel length using the ported cylinder and the 2.22:1 ratio with a 6.03mm barrel is 189mm.

If you are not keen on all the maths then just use this website. At the bottom there is a Cylinder to Barrel Ratio Calculator: AirsoftTech.dk - Calculator to calculate, Speed, Rate of Fire, Gearsets, etc.
NOTE: This calculator says that the cylinder diameter is 23.5mm. Most cylinders are actually 23.8mm. So make sure you change it.

Here are the most efficient ratios for a V2.5 gearbox (SR25)
SR25 Cylinder Ratios using 6.03mm barrels
BB weight-----Barrel Length-- Barrel Volume----- Ratio
0.2gm------------505mm---------14336mm3------2.17:1
0.23gm----------502mm---------14193mm3-------2.19:1
0.25gm----------495mm---------13993mm3-------2.22:1
0.28gm----------490mm---------13908mm3-------2.24:1
0.30gm----------484mm---------13708mm3-------2.27:1
0.32gm----------467mm---------13279mm3-------2.36:1
0.36gm----------442mm---------12565mm3-------2.48:1
0.40gm----------414mm---------11709mm3-------2.65:1
0.43gm----------402mm---------11423mm3-------2.73:1
0.45gm----------391mm---------11080mm3-------2.81:1

Happy teching
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Last edited by 1tonne; 11-30-2019 at 02:28 PM.
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Old 08-12-2018, 12:56 AM   #2
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Old 08-12-2018, 11:43 AM   #3
 
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Just going to stick this.....
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Old 09-04-2018, 01:05 PM   #4
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Edit: to be continued

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Old 09-04-2018, 02:17 PM   #5
 
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This was in response to Leetworlds post, but he edited his post and I am not going to rewite this....

Why would the math be any different from a BASR to an AEG? You are calculating the volume of something does not matter if its a bolt action, AEG, or some crazy high speed hydraulic ram on a battle bot. That math will not change.

The only major difference between an AEG and BASR is how you compress the spring, or "energize it." You either overcome the springs resistance threw your own strength, or you use electricity to run a motor and gear train to do it. Neither of these effect volume in anyway. This only effect the cycle time and system efficiency.

=======

To directly answer the "Are AEGs superior in every way?" That is not a truly easy question to answer.

In a very basic way, yes the AEG is superior. The more dawn out answer, "depends." Boils down to materials, quality of said materials, quality of manufacture processes, and design.

Looking at this question from an origin stand point, (1J, same hopup design, fixed hop) then the AEG will win every time basically. (So long as input energy is infinite and not factoring in wear...) However we all know it is not that black and white.

For us in other regions of the globe, power regulations are different, this changes the question of "is an AEG better then a BASR?"
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Old 09-04-2018, 04:11 PM   #6
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I agree, PB...the list of variables of one platform vs. the other is absolutely vast. The only differentiating feature in the BASR is the higher fps allowance. Other than that, if we're firing the same ammo, then theoretically, we should be able to get the exact same performance.

In reference to accuracy, I do think rate of fire affects accuracy to some degree on some builds..and not as much of an advantage as you might think. Still compiling data..
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Old 09-04-2018, 05:07 PM   #7
 
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That higher FPS allowance is a site by site thing. Which further muddies the water as to which is better. Its a question that has many answers that are all correct to some degree.
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Old 09-04-2018, 05:16 PM   #8
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Maybe it's like the fly rod or golf club thing...whatever works that day is best...
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Old 09-04-2018, 06:04 PM   #9
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Quote:
Originally Posted by Zero Roaster View Post
In reference to accuracy, I do think rate of fire affects accuracy to some degree on some builds..and not as much of an advantage as you might think. Still compiling data..
It may but that would just be from the vibration. A fast semi auto cycle time however shouldn't make any difference. It still fills the cylinder with air unless it has super high RPS.
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Old 09-04-2018, 06:30 PM   #10
 
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I wonder if a revisit to the PDI vacuum piston head for AEGs in a DSG build would be of worth?
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Old 09-04-2018, 07:10 PM   #11
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Originally Posted by Plazmaburn View Post
I wonder if a revisit to the PDI vacuum piston head for AEGs in a DSG build would be of worth?
I don't think it would be worth it (could be wrong). An AEG piston o-ring releases it's pressure once it has stopped moving forward and air can come from behind it. That is pretty much the same as the PDI Vacuum Piston.
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Old 09-05-2018, 12:17 AM   #12
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Quote:
Originally Posted by Plazmaburn View Post
This was in response to Leetworlds post, but he edited his post and I am not going to rewite this....

Why would the math be any different from a BASR to an AEG? You are calculating the volume of something does not matter if its a bolt action, AEG, or some crazy high speed hydraulic ram on a battle bot. That math will not change.

The only major difference between an AEG and BASR is how you compress the spring, or "energize it." You either overcome the springs resistance threw your own strength, or you use electricity to run a motor and gear train to do it. Neither of these effect volume in anyway. This only effect the cycle time and system efficiency.

=======

To directly answer the "Are AEGs superior in every way?" That is not a truly easy question to answer.

In a very basic way, yes the AEG is superior. The more dawn out answer, "depends." Boils down to materials, quality of said materials, quality of manufacture processes, and design.

Looking at this question from an origin stand point, (1J, same hopup design, fixed hop) then the AEG will win every time basically. (So long as input energy is infinite and not factoring in wear...) However we all know it is not that black and white.

For us in other regions of the globe, power regulations are different, this changes the question of "is an AEG better then a BASR?"
I agree with the above. It’s not the point I was making. That’s what (and more) baffled me but you could say I was baffled so much, I couldn’t make a straight constructive point..... therefore to be continued
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Old 09-05-2018, 08:51 AM   #13
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It may but that would just be from the vibration. A fast semi auto cycle time however shouldn't make any difference. It still fills the cylinder with air unless it has super high RPS.
No, not just from vibration. COnsider the pumping action of the cylinder/piston assembly. Where it draws air from, and the correlation with barrel length as well as rate of fire. Not even necessarily considering two BB's in the barrel at the same time, but also system stability between shots and the turbulence of the air and how long it takers to dissipate and restabilize between shots.

Ultimate system accuracy would occur when pressures are all equalized, the air in the barrel system is static and steady, and the machinery is at maximum potential. For example, all pressure is equalized and the system is cocked. So now the question is to measure how long it takes for the system to reestablish itself between shots. It's probably longer than you think...
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Old 09-05-2018, 09:25 AM   #14
 
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Originally Posted by 1tonne View Post
I don't think it would be worth it (could be wrong). An AEG piston o-ring releases it's pressure once it has stopped moving forward and air can come from behind it. That is pretty much the same as the PDI Vacuum Piston.
I think I am still going to play with it and see what it does in a DSG build. I am not expecting much out of it. But you never know. I think I will need to completely remake it though as I do not want to wreck my original one and make some tweaks to it. Hmm... half the volume, barrel... This project is going to be silly...
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Old 10-23-2018, 06:26 AM   #15
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Hey everyone,

So, there has been a lot of talk about cylinder:barrel ratio in the past few years and I am really glad that airsoft community finally got proper results with 1tonne's experiment.

But I am confused about how low of a cylinder volume can I go before I lose in performance, assuming I've got correct ratio for the bb?

So, for example would two AEGs with the same cylinder:barrel ratio, but different cylinders (type 0 and 3) and barrel length (respective barrels) be comparable in performance?
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