M120 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 ~380-390 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.