[Predator]

I have an G&P M4 SR16 w/reinforced gearbox, and one piece metal hop up on mine. If you ask my gunsmith, he'll tell you it was a bitch of a time putting it on, then again, the most troubles he had was the internals with the gearbox since the metal body from G&P often comes with one, as it was meant to fit with their metal body. Correct me if I am wrong somebody.