7mm upgrade spring for sniper rifles -M150 (500 FPS)

Spring for airsoft sniper rifles. It is made of spring steel with proper heat treatment and gives the final output of about 150 m/s (500 FPS). The spring has an inner diameter of about 7.5 mm and an outer diameter of 10.2 mm. The length is 251mm. It is therefore dimensionally suitable for most plastic basic piston