M130 main spring
The main spring is designed to be used in tune ups of the electric replicas (AEGs), the spring is uneven, what significantly extends the lifespan of the system by minimizing the spring's clumping effect, of course under the condition that the spring is mounted in a proper manner. It is made by the well known G&G company.
In a typical system, the spring allows to fire the BB pellet with the muzzle velocity of about ~414-425 FPS. Yet it is important to remember that the final muzzle velocity gained by the mount of the spring depends on the sealness of the system, the type of the used cylinder, the length of the barrel and its diameter. The ends of the spring were grinded what results in its better operation.