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.
The SOTAC L3 NGAL is really well made and is probably 1 of the best of its type on the market today, I have nothing bad to say about it, I order from sixmm often & have for a couple of years now & will continue to use them hopefully for many years to come