Matrix Airsoft Mock Silencer / Barrel Extension (Model: The Boo / 180mm)

"These mocks are somewhat fine. I ordered two. And there light weight and feel somewhat fragile, so if you need something for looks and not too heavy. These are for you. If you need a silencer with a good sturdy enough weight and won't be afraid to toss them around. These aren't for you

"i have an m4 with a standard barrel. If i buy this how long should i make my inner barrel?