This KKF exclusive gas system (pat. pending) for the M16/AR15 family increases reliability, runs MUCH cleaner through the use of an op-rod system, bleeding no barrel gasses back into the action, and runs smoother. Easy operator takedown if maintenance is ever neccessary. Components are machined from hardened stainless steel and titanium. Karbine and mid-length system assemblies and tuned uppers available 01/2007. KKF can upgrade your existing system to the KKF M9Evo for the special  introductory price of  $395/INSTALLED. Complete BM-based uppers: 14.5" M4-$895 (prices subject to change without notice).  THIS is the system that launched a new industry from others who came in late. Why pay more? Go with the original and the best. From Swamp Manufacturing Industries (SMI). Lifetime guarantee. 

Note: This system fits under standard M4 HG's (CAR, M/L, & Rifle), Daniel Defense HG's (but not the M4 w/o modification) & LaRue HG's (available on a package soon!), among others. To illustrate:

 It will not fit under the standard 1 3/4" inside diameter  tubular aluminum HG's or standard 2-piece carbine, M/L, & Rifle HG's commonly found.