The GBB M4 120% Hammer Spring is an upgraded spring for gas blowback AR15 airsoft guns.
This spring fits most GBBR M4s, and increases velocity by increasing gas released behind the BB. The 120% hammer spring will produce different results depending on what other components it is paired with and what rifles it is installed in.
GBB M4 120% Hammer Spring Features:
-Fits most GBB M4 Airsoft Guns