CO2 airguns are engineering marvels for their size. A tiny 12-gram cartridge can fire 50–80 rounds with surprising consistency. But how? Here is a step-by-step breakdown of the full mechanical and physical process.
Step 1: The CO2 Cartridge
A standard 12g CO2 cartridge is a sealed steel cylinder containing liquid carbon dioxide under pressure (~850 psi / ~58 bar at room temperature). At room temperature, a portion of the CO2 remains as a liquid while the rest is in gas phase above it — this is called a two-phase system.
This is important: because liquid CO2 is constantly evaporating to replace gas used, the pressure stays nearly constant until the liquid is almost exhausted. That is why the first 40–60 shots from a fresh cartridge are consistent, and the last few shots drop in velocity as only gas remains.
Step 2: Piercing the Cartridge
When you install the cartridge and tighten the cap (or push the loading lever), a sharp steel pin inside the gun's gas cylinder pierces the foil seal on the neck of the CO2 cartridge. This creates a direct channel between the cartridge and the gun's internal gas system. A small seal (o-ring) around the piercing pin prevents leakage.
Step 3: The Valve System
Between the cartridge and the barrel sits the heart of the CO2 gun: the exhaust valve (also called the firing valve or power valve). This valve is spring-loaded closed. At rest, it blocks the flow of CO2 gas.
The valve has two sides:
- High-pressure side: CO2 from the cartridge (58 bar)
- Low-pressure side: The barrel (ambient)
Step 4: Cocking and the Hammer
When you cock the gun (via the slide, hammer, or lever), you are compressing a second spring — the hammer spring. This stores mechanical energy. A sear catches and holds the hammer in the cocked position until you pull the trigger.
Step 5: Firing
Pulling the trigger releases the sear. The hammer spring drives the hammer forward. The hammer strikes the stem of the exhaust valve, briefly forcing it open against its own spring pressure. In that fraction of a second (typically 2–4 milliseconds), a controlled burst of high-pressure CO2 gas rushes through the valve and into the barrel behind the pellet or BB.
Step 6: Gas Expansion and Projectile Launch
The sudden release of CO2 at ~58 bar into the low-pressure barrel creates a rapid pressure differential. This expanding gas pushes the pellet or BB down the barrel at high velocity. By the time the projectile exits the muzzle, the pressure has dropped significantly, which is why a longer barrel generally yields higher muzzle velocity (more time for gas to accelerate the projectile).
Why Does Cold Weather Reduce Performance?
CO2 pressure is directly related to temperature. At 20°C, cartridge pressure is ~58 bar. At 10°C, it drops to ~45 bar. At 0°C, it falls to ~35 bar. Lower pressure means less force behind each shot — lower FPS, and potentially unreliable feeding on semi-auto models. This is why CO2 guns underperform in winter.
The Shot Count
A 12g CO2 cartridge typically contains enough gas for 40–80 shots depending on:
- Barrel length and valve size
- Ambient temperature
- Whether the gun fires single or double-action
- Calibre and pellet weight
Now that you understand how they work, browse our full range of CO2 airguns or stock up on CO2 cartridges and accessories.