Hop-up, (High Operation Power Up), is basically describes the back spin trajectory of an BB pellets, by adjusting the Hop-Up to increase their range and accuracy.As the pellet shoots through this hop up bucking, the friction creates the spin, it tends to roll and backspin.

VFC Hop Up Rubber For KAC SR25 ECC/ M110 GBB Rifle (Part# 07-7)
Rubber Made
Design For Replace the Original Parts
Suitable for KAC SR25 ECC/ M110 GBB Rifle Airsoft Guns