This is an HK-51 built by RGS on an FMP (Portugal) reciever. These recievers are built on actual HK tooling and are no longer importable. It has the flapper mag release installed and utilizes the latest truncated cocking tube. The barrel is cut down to 8.31 inches and threaded. A fake suppressor is pinned onto the gun to bring it up to legal length. This is easily removable after SBR registration. Feel free to email me for pics or with any question.