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Optimal Cylinder to Barrel Ratio [Simplified Airsoft Guide]


What is cylinder to barrel ratio in Airsoft?

To simplify, the piston inside the cylinder pushes air into the barrel which makes the BB fly out of the barrel. Off the bat, you might think that the more air pressure the better, but that’s not exactly the case. There are two important aspects that need to be considered when optimising this in your replica – the mentioned air pressure and volume ratio between the cylinder volume and inner barrel volume. The air pressure can be easily improved by upgrading to a stronger spring and ensuring good air seal. 

Created by “Cheesehead” on Airsoft Retreat. Above GIF is public domain on AirsoftRetreat.com

Compression Point

When the final (sector) gear releases the piston when the trigger is pulled, the piston then starts travelling down the cylinder towards the nozzle. As as soon as it fully passes the hole in the cylinder, the piston then starts compressing the air in front of it. This is exactly where the “compression point” is. Now this is where the two important volumes of air are created when you shoot your replica:

Cylinder Volume

It’s the volume of air inside the cylinder during the compression point to where it hits the cylinder head and then passes through the nozzle.

Inner Barrel Volume

The volume of air travelling through the barrel and out the barrel surrounding the BB in the first section of flight.

Read More: make sure to see our ‘Comprehensive Guide to Airsoft Inner Barrels’ where we cover the importance of appropriate length/diameter and other extra tips for best possible range and accuracy. 

Volume Ratio

So the ratio between the cylinder volume and the inner barrel volume is called the volume ratio. This is what you want to be optimising in the process. Volume ratio alongside air pressure are the factors that determine the speed and stability of the BB when it exits the barrel. These need to work in agreement with each other to produce the most consistent results with each shot. Here’s why:

High Volume Ratio

If the ratio is too high, the moment the BB leaves the inner barrel, there will still be a lot of remaining high pressured air behind it. This high pressure air will then dash out the barrel faster than the BB, surrounding it and applying random spin. This is crucially bad because random spins will not allow for accurate consistency between shots, meaning you will really struggle to hit a target at a longer distance.

Optimum Volume Ratio

The logical thing to say is that 1 to 1 ratio would be perfect in that case. Unfortunately not. That would mean the BB would leave the barrel with no pressured air behind it at all. What we should be aiming at is to find the volume ratio which allows for the pressured air to exit the barrel at exactly the same speed as the BB itself. This will ensure that the pressurised air will not knock the BB off its center and thoroughly guide it out the barrel and into its flight path.

Low Volume Ratio

If the ratio is too low, then the pressurised air will not travel all the way down the barrel; meaning it’s not reaching its full potential speed and not guiding the BB all the way through and in fact might be marginally pulling it back just before it leaves the barrel. This might decrease FPS and certainly will decrease range to some extent. 

Cylinder Types

Type 0 cylinders – these cylinders do not contain any ports (holes in the cylinder)

Type 1/2 cylinders – these cylinders contain ports halfway down the cylinder

Type 3/4 cylinders – these cylinders contain ports 3/4 of the way down the cylinder, measured from the front (or cylinder head end) of the cylinder

Type 4/5 cylinders – these cylinders contain ports 4/5 of the way down the cylinder, measured from the front (or cylinder head end) of the cylinder

Bore-up kits – these kits contain completely new parts (cylinder, cylinder head, piston head, air nozzle) which have been designed to allow for a larger volume of air to be stored and pushed down the barrel. These kits are intended for use with very long barrels generally exceeding 600mm.

Recommended Brands of Cylinders

High quality cylinders are often out of stock, therefore we recommend searching Ebay and Amazon for your desired product and either snatching them up or at least adding them to your wish list. Otherwise, have a look through airsoft retailers, we thoroughly recommend Fire-Support.co.uk and Camoraids.co.uk

Recommended Barrel Lengths with each Cylinder Type

Please treat this as a rough guide; this recommendation might not be perfect for your specific replica. There are other factors that come into play, as mentioned previously, the airseal in your replica and the spring strength, for example. This is a very much ‘trial and error’ process when optimising the Volume Ratio; stay patient and keep trying! Here is our list of ranges of barrel lengths which are generally optimum for these cylinder types:

  • Type 1/2: 110-170mm
  • Type 3/4: 270-430mm
  • Type 4/5: 364-460mm
  • Type 0: 450-600mm+

This article is part of AEG Wiki, please click here to see the master article written by us.

How to fix an incorrect Volume Ratio?

If you find that your replica shoots very inconsistently with each shot, or the range is simply too short and you already have upgraded your hop-up, spring and ensured good airseal. Then incorrect volume ratio might be the problem. There’s two simple ways to tackle this issue; either change the inner barrel according to the cylinder size, or change the cylinder according to the inner barrel length. 

To increase the ratio, you can get a cylinder with a higher volume from the next up type – meaning if you currently have a cylinder type 1/2, simply get the next one up from type 3/4 . Alternatively, keep the current cylinder the same and purchase a shorter inner barrel. 

To decrease the ratio, do the exact opposite. Get a cylinder with a lower volume from your current type; e.g. go from cylinder type 3/4 to type 1/2 or purchase a longer inner barrel.

Final Words

We hope you found this article helpful, if you feel like any section wasn’t explained well enough or you think we missed something out. Please feel free to comment your suggestions or simply start a new thread in our dedicated forum!

Have an awesome day Ranchers!

Written by Kamil Turecki

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