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.

Here are the 2 sections:

LT-103B Full Metal AK

Starts at 0:24
Tools you’ll need: 2.5mm hex wrench
Version 3 Gearbox

LT-101 Multi Mission Carbine

Starts at 1:40
Tools you’ll need: 2.5mm hex wrench
Version 2 Gearbox"