The latest video from RA-Tech are these steel outer barrel made for the CZ75 and M93 gas blowback pistols and stainless steel recoil buffer for M4 gas blowback rifles.  The recoil buffer was tasted on a KSC M4 PTS GBB rifle which shows an impressive recoil for those who want a good kick from their gas blowback M4s. These are available now at the Airsoft Taiwan online store with links provided below the embedded video.

RA-KSC Cz75 CNC STAINLESS Outer Barrel

RA-KSC M93R CNC Steel Outer Barrel