Learn › Track 02 · Equipment & physics

Spring, CO2, SSP, PCP

Every match air pistol has the same job: push a 4.5 mm pellet down the barrel at about 150 m/s. There are four ways to store the energy for that push. If the pellet comes out at the right speed, why should it matter which one your pistol uses?

Think first: Same shooter, same pellet, same target. Why does the way the pistol makes its air matter?

  • It mostly changes how loud the shot is
  • Anything that changes from shot to shot, or moves the pistol before the pellet leaves, moves the hole on the target
  • Only top speed matters, and all four systems reach it

Four ways to make a shot

Pick a system and press Fire. Each animation is slowed right down. In real life the whole thing is over in a few thousandths of a second.

Simplified cross-sections, not to scale. The pellet sits at the start of the barrel on the right. Pressure is shown in orange.

Spring piston

Cocking the pistol compresses a strong spring. When you fire, the spring drives a piston forward, squeezing a pocket of air behind the pellet. The problem is the order of events. The piston slams to a stop and the pistol reacts before the pellet has left the barrel. Feinwerkbau’s FWB 65 used a sliding “sledge” to cancel that kick, and it stayed in production until 1997. But spring pistols always punished poor follow-through.

CO2

A CO2 pistol has no heavy piston. A cartridge holds liquid carbon dioxide with gas above it, and a hammer knocks a valve open to release a puff of gas. The catch is that the gas pressure depends on temperature, not on how much is left. As long as there is liquid in the cartridge, the pressure is set by how warm it is.

Think first: CO2 is about 57.3 bar at 20 °C and about 72.1 bar at 30 °C. By roughly what percentage does the pressure rise?

CO2 pressure against temperature. Above 31.1 °C (the critical point) CO2 can no longer exist as separate liquid and gas. The velocity and impact numbers come from this site’s simple model, zeroed at 20 °C.

In our model, a pistol zeroed at 20 °C prints a few millimetres high at 30 °C. A few millimetres is several decimal bands. That is why CO2 lost out to air.

Single-stroke pneumatic (SSP)

An SSP pistol makes its own air, one shot at a time. Before each shot you open and close a lever, which compresses a single charge into a chamber. The same stroke gives the same charge, and air pressure hardly cares about room temperature. Feinwerkbau’s 100 series (1988–2008) was the classic example. The FWB 103 shot at about 154–158 m/s. The cost is effort and time: you pump before every shot, sighters included.

Pre-charged pneumatic (PCP)

A PCP pistol carries its air in a cylinder filled to 200 bar. A regulator cuts that down to a lower, fixed pressure and refills a small chamber after every shot. When you fire, a hammer opens the valve and that same charge pushes the pellet. You get no piston slam, no pumping, little sensitivity to temperature and almost no recoil. One cylinder lasts roughly 110–200 shots, and you can carry a spare.

Side by side

  • Spring piston — Self-contained: no gas, no air source · Piston moves the pistol before the pellet leaves · Must be cocked before every shot
  • CO2 — No heavy moving piston · Pressure rises about 26 % from 20 to 30 °C · Rapid shooting chills the gas and slows the pellet
  • Single-stroke (SSP) — Same charge every shot, little temperature effect · No tanks or pumps to buy · A pump stroke before every shot
  • Pre-charged (PCP) — Regulated, steady charge every shot · No cocking effort, almost no recoil · Needs a high-pressure air source · Cylinders expire, and seals and regulators need servicing

PCP pistols won because they fix the problem that matters most: they give the same shot every time. Their weaknesses are practical ones. You need a way to fill the cylinder, and the cylinder and its seals need care. The next three lessons cover exactly that.

Think first: Your PCP pistol’s gauge drops a little overnight, and a chronograph shows its velocity wandering more than it used to. Which parts would you suspect first?

  • The barrel and the rifling
  • The seals and the regulator
  • The sights
  • Spring pistols move before the pellet leaves, which punishes poor follow-through.
  • CO2 pressure follows temperature: about 57 bar at 20 °C and 72 bar at 30 °C, up 26 %.
  • Single-stroke pistols give a steady charge but need a pump stroke every shot.
  • PCP: a 200 bar cylinder and a regulator give the same charge every shot. You need an air source, and the seals and cylinders need care.

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