For VSR-10.Body & head are made of Delrin,end is made of Stainless.That's not only light but also
high durability.Head is the intake air type.When piston go ahead,the O-ring is spreaded that the air flow in the head.There is no clearance for Cylinder,that's why it keeps airtight.

Inner Diameter is about 13.5mm

If use this piston , available to PDI FAT dia.spring series (But not for high power spring,SS,SPR & VSR over 1J setting)
Normal Spring Guide is not abailable.Please take 9mm SPRING GUIDE.
Caution:
This piston is made for PDI-Precision cylinder,not for original cylinder, Raven cylinder & other brand's.

If you use power spring as SS,SPR or VSR high power spring,please select all metal piston. This has no durability using with their springs.

Vacuum system
Vacuum system is to let fly at BB more farther and go straight.
This system erase the negative pressure when shooting.The system is inside the head.
1.Conventionally,the valve is free in the system.(This is not air sealing)
2.When shooting,the piston go ahead.At that time,The valve closed & start to keep air sealing.
3.As well as the piston bump against the cylinder head,the valve come off.
4.The air flows toward top from rear.This cancel the negative pressure.