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.
I received something other than what I ordered and paid for. Instead of the Sotac Micro 3x, I received a Swamp Deer G43. The promise to return the difference has not been fulfilled so far.