Gas Blowback Rifle Conversion Kit- Angry Gun, HAO, Maddog, and RA TECH are providing the kind of Conversion Kit such as the HK416D kit, John Wick M4 Rifle Kit, Noveske N4 Rifle Kit.
Just settle for the guarder version, the trigger bars come warped and I had to donate my tm bars and the trigger itself varies. One works fine and the other one is too large. avoid