Volume Ratio

Volume Ratio (also known as Barrel:Ratio) refers to the ratio between the internal volume of the cylinder and the volume of the inner barrel in an airsoft gun. This ratio plays a crucial role in determining how efficiently the BB is accelerated by the air pushed out by the piston.







How Barrel:Ratio works

When you pull the trigger, the sector gear releases the piston, which begins to move forward inside the cylinder. As the piston passes the last port in the cylinder, air starts to compress – this point is known as the compression point. The air volume between this point and the cylinder head is called the cylinder volume, while the volume of the entire inner barrel is the barrel volume. The ratio between them determines how efficiently the BB is accelerated.





Consequences of too low or too high Barrel:Ratio

  • Too low ratio (e.g. below 1.5:1): The air runs out before the BB exits the barrel. This means the BB is not fully accelerated throughout its travel, reducing performance and consistency.
  • Too high ratio (e.g. above 3.5:1): When the BB exits the barrel, there's still a significant excess of pressure. This can cause turbulent air to swirl around the BB and disrupt its trajectory, resulting in lower accuracy.







Optimal ratio values

  • A ratio between 2.0 and 2.5 is generally recommended.
  • For longer barrels and precision barrels with a narrower inner diameter, a higher ratio of 2.5 to 3.5 may be suitable.
  • A 1:1 ratio is not ideal – the goal isn’t zero pressure behind the BB, but rather that air exits the barrel at the same time as the BB, with no excess pressure.
  • You can estimate your ratio value using this LINK (in English).




How to adjust Barrel:Ratio

  • To increase the ratio: Use a larger cylinder (no port or with a larger bore-up diameter), or choose a shorter inner barrel (or lighter BBs).
  • To decrease the ratio: Use a ported cylinder with a port closer to the cylinder head, or a longer inner barrel (or heavier BBs).
  • The inner barrel diameter has a small effect on the ratio, though the impact is minimal despite expectations.