Rocket Airsoft M160 AEG Spring

Rocket Airsoft M160 AEG Spring. Silver type upgrade spring that is non-linear.  Fits in all gearboxes.  A higher FPS than most for heavy duty upgrades.  FPS will be north of 520, maybe around 530 or so. For heavy upgraded guns, DMR, etc only.  Experienced techs only. (please note: packaging may be generic or labeled as 'Rocket Airsoft', but is made by SHS OEM)