Daniel Defense MK18 RIS II Rail System

Current production Colt upper receiver group with DD RIS II barrel nut.
(Correctly installed using the SA wrench pictured)
Note:  The entire front sight base has been intricately machined to fit inside the DD rail dimensions.
Colt factory gas system - No aftermarket gas-blocks or set-screws. 

(Shop Service - DD RIS II Gas Block)
 Colt upper receiver group completed and ready to fire