Elite Force

Elite Force Complete Gearbox w/ CFR Spring

ARES

Amoeba Complete ECFS Version 2 Rear Wired Gearbox

VFC

VFC ECS Complete Gearbox Gen 2

ICS Airsoft

ICS CXP-MARS Lower Gearbox w/ SSS

Umarex

Elite Force H&K VFC 416/C, M27, 4CRS/L Complete Gearbox with MOSFET

ICS Airsoft

ICS EBB Lower Gearbox w/ SSS (UK1/HOG/YAK/CS4)