Latest Daniel Defense RIS Rail release from MadBull Airsoft... "We are very proud to make authorized Airsoft version for Airsoft players. (Airsoft version can’t apply to real firearms. Internal dimension changed and materials are different.) You can easily mount float an M203 toy grenade launcher on your M4 rifles. Black color and limited quantity Flat Dark Earth (FDE) are available at the same time.

Description from DD official website:

Daniel Defense is the Sole Source Provider of the RIS II to the United States Special Operations Command! (SOCOM).

The Daniel Defense MK18 RIS II is designed to work specifically on the MK18 CQBR!

The Daniel Defense Rail Interface System (RIS II) was designed at the request of the United States Special Operations Command (SOCOM) for the SOPMOD II program. SOCOM had a specific requirement for a free float M203 solution and Daniel Defense responded, designing a revolutionary product to meet the government’s need."