If you want to disable the blowback function in your M4 or AK AEG, here is a tutorial video in the Tech Bench Series of Lancer Tactical... "This episode of The Tech Bench will show you how to disable the blowback on two Lancer Tactical Airsoft Guns: the LT-103B Full Metal AK (Version 3 Gearbox) and the LT-101 Elite Multi Mission Carbine (Version 2 Gearbox). The blowback on the Advance Recon Carbine can also be disabled in the same manner as the MMC.