The roller-delayed blowback action is similar to that used in the G3 battle rifle and is the hallmark feature of Heckler and Koch's pre-G36 line of small arms. The four groove barrel features polygonalrifling with a right-hand twist of 1 in 10.6 inches. The chamber is fluted with 12 longitudinal flutes extending rearward from the baffle to the chamber face. These flutes permit propellant gases to flow around the case acting as a lubricant to ease extraction. The SL6 has a diopter sighting system and utilizes Heckler and Koch's proprietary HK 05 claw-type scope mount. Two rectangular recesses have been cut into the upper receiver to accept this mount.
The H&K SL6 is no longer manufactured, having been replaced by the H&K SLB 2000. The H&K SL7 is a variant chambered in 7.62×51mm caliber. The H&K SL6A2 variant is essentially the same rifle; however, the SL6A2 includes a flash hider and offers a two round burst selector.