[Akami]

Okay context lol

I am thinking of doing DIY SSG, and when it comes to the cylinder, which do you think is better, big diameter or long length?

Personally I want to use TM L96 length cylinder to keep the gun short so it could be put in storage easier, which means I'll use big diameter.

But what do you guys think?

 

[RonSwanson]

My current theory is that a longer cylinder is more air efficient than a shorter wider one. (Assuming air volume is the same).

Because it's longer it should take longer for the piston to release and reach cylinder head (so use all air volume). Also as a side effect with a more efficient setup weaker springs can be used.

Now only proof of this I have is the fact that type96 rifles can use longer barrels than a vsr even though they have slightly less volume. And a longer barrel is theoretically going to provide more output energy if matched to cylinder air volume correctly.

But again mostly theory at this point as no one has truly tested

 

[Sodium]

Longer is more efficient. The aps rifles with longer cylinders, while not doing as well as the vsr, do much better than they should based on 1tonne's cylinder calculations. That said, more volume always helps too.

 

[Akami]

So in theory APS2 system with as much volume as a VSR could perform even better than VSR?

 

[RonSwanson]

So in theory APS2 system with as much volume as a VSR could perform even better than VSR?

Wouldn't say better more like more efficient as longer barrel that can be used effectively=more time for bb to gain energy=lower powered spring needed=quieter and easier.

Logically I would assume that a minimum air volume is needed to launch each BB weight (heavier=more volume) but no on has tested that yet and both platforms handle current weights without issue it seems.

Wonder if anyone with a striker could chime in if they've had trouble with heavyweights.

 

[BlackDogAirsoft]

Previous thread where we talked about this:

Interesting article on Air rifles...perhaps applicable...

The article discusses how altering piston weight and cylinder volumes can make an air rifle more efficient. Curiously, the cylinder volume is decreased, and the piston is lightened. https://www.airgunmagazine.co.uk/features/a-perfect-formula-airgun-design-breakthrough/

www.airsoftsniperforum.com

 

[1tonne]

One thing to think about with a longer, wider cylinder that has more volume, is that if there is too much volume, you may need an extra-long inner barrel to match the cylinder to barrel to bb weight ratio. But this is OK because you can then port the cylinder. So, you can then shorten the barrel to a desired length and then port the cylinder to have the correct amount of air for the barrel and bb weight. The advantage of this is that the piston will accelerate more before compression starts. Thus, giving you very high fps with a lighter bolt pull.

 

[Akami]

you may need an extra-long inner barrel to match the cylinder to barrel to bb weight ratio.

What if I use wide bore like orga?

The advantage of this is that the piston will accelerate more

Wouldn't it affect the ideal joule output? You know, the correct piston weight thing, where we want the piston to move not too fast and not too slow

 

[SiliconeSword]

The use of a widebore seems a bit of a waste, as you could simply just use a weaker spring or port the cylinder(last resort option) and achieve similar results but with either a better bolt pull or less sound.

 

[1tonne]

What if I use wide bore like orga?

You could use a wide bore if you wanted but wide bores are a waste of energy. I have found no difference in accuracy between rifles of the same energy rate that have different bore diameters. Some people say otherwise but I have never noticed it and I have done hundreds of experiments.

Wouldn't it affect the ideal joule output? You know, the correct piston weight thing, where we want the piston to move not too fast and not too slow

I don't think that a high piston speed makes the rifle inaccurate. It is more if the speed of the bb is too much for its mass. (This could be incorrect, but it is what I think at the moment unless someone can convince me otherwise). So, on these forums you will see a lot of people say that any rifle shooting above 4 joules is not worth it (unless using ceramics). So, to bring the speed of the bb down in a rifle that has excess air, you could port it to have the perfect volume for the bb. You can then use a weak spring to get a high energy rate because the piston has already sped up more than it would have if the cylinder was un-ported. Thus, making the rifle easy to rack.

 

[nearsighted_ash]

Okay context lol

I am thinking of doing DIY SSG, and when it comes to the cylinder, which do you think is better, big diameter or long length?

Personally I want to use TM L96 length cylinder to keep the gun short so it could be put in storage easier, which means I'll use big diameter.

But what do you guys think?

The answer is it depends on many factors, but I'll talk about the most impactful factors IMO which are

• Spring strength
• BB weight
• Barrel dimensions (diameter and length)
• Hopup dimensions (I've decided I need more time to think about this factor so I won't mention it in this post)

Here I'll try to explain the impact of each factor on each type of cylinder and determine the potentially optimized combination of said factor for both BIG and loooooooooong cylinder guns.

TL;DR:

• BIG (wide) cylinder does not work well with weak spring, it needs strong spring. It also prefer lighter BBs and have and edge over loooooooooong cylinder when pairing with short/wide barrel.
• loooooooooong cylinder can work well with weaker spring unlike the BIG one. It prefer heavier BB and long/tight barrel when paired with a strong spring.

WALL OF TEXT:
Now I'll assume both our BIG and loooooooooong cylinder guns will have 100% airseal, same 5mm air nozzle diameter to maximize airflow, same piston weight, and same cylinder VOLUME.

*First, let's talk about the BIG cylinder. To get the most out of a BIG cylinder, we usually need a stronger/harder spring. A BIG cylinder (wide diameter) means a bigger surface area --> more air resistance + more air is bottlenecked at the tight little air nozzle, hehe boi. But there is a limit of how fat a BIG cylinder can be, beyond that, the bottleneck resistance becomes too much to push through and it just wouldn't work, but don't worry, I don't think there is a gun big enough to use such a BIG cylinder.

Bottleneck

So when the piston is released, it will create "a sharp spike/short burst of pressure" with a strong spring, whereas a weak spring will not be able to overcome the bottleneck resistance and will push the piston too slow to be effective.
This sharp spike of pressure means a lot of pressure is putting on the BB in a short time, this is good for achieving high fps when shooting lighter BB. Heavier BBs have more inertia, so a short burst of energy from a BIG cylinder would not do well unless you compensate that with a lot of volume to extend that burst. Even then, a loooooooooong cylinder with the same air volume would do better pushing heavy BBs and I'll explain why later.

Rough illustration of the sharp spike pressure

Next, a BIG and loooooooooong cylinder would do well on both tight/long barrel since tight barrel would hold the pressure pretty well throughout its length so it doesn't matter much as long as there is pressure behind the BB, it will shoot well. However, the BIG one would have an edge pairing with a short/wide barrel. A short/wide barrel like the Orga one doesn't hold the air pressure well since all the air would escape very quickly around the BB. That means in this setting, most of the BB energy is achieved shortly after leaving the hopup chamber, so a short burst of energy achieved from a BIG cylinder would suit this setting more, while an extended release from a loooooooooong cylinder would not be very effective unless very overvolumed (high volume fix most problem yayy) but even then a BIG cylinder would do much better with such high volume.


*Enough talk about the BIG cylinder, now we move on with the loooooooooong one. Again, we'll discuss spring strength on loooooooooong cylinder. Generally, you'd want a strong spring on your sniper but not too strong destroy your gears. We already know that BIG cylinder offers more resistance due to the bottleneck effect, that acts similarly to an airbrake so you can use stronger spring without breaking your gear. A loooooooooong cylinder would not offers that much resistance due to a smoother bottleneck. For this reason, the same weaker spring would do much better with a loooooooooong cylinder than with a BIG cylinder.

But it is not impossible to use stronger spring on loooooooooong cylinder and not breaking your gear, this is where heavy BB and long/tight barrel come into play. Heavy BB and tight barrel will offers the resistance that the loooooooooong cylinder lacks.

Loooooooooong cylinder also compress and release gas slower and more extended so it would accelerate a high inertia/heavy BB much better than a sharp spike of pressure.

Please ignore the text as I can't find better picture, the sharp spike of pressure produced by a BIG cylinder (yellow) compare to an extended spike (purple) of a loooooooooong cylinder.

Also, the slower rate of release means slower energy transfer => requires more time underpressure to accelerate the BB, so a long/tight barrel would be a perfect match for a loooooooooong cylinder. The long/tight barrel offer more time underpressure for the BB. Also since it keep the pressure better than short/wide barrel, the long/tight barrel would dampen the force of a stronger spring so your gear would last longer.

*In conclusion, both BIG and loooooooooong cylinder are good in different settings and there isn't a clear better choice. You have to choose them according to your preferred setting.