The M6A1 SL, in 5.56 x 45mm caliber, is a basic piston rifle. SL stands for stretched piston system in a lightweight configuration. It has a 14.7" lightweight profile barrel and comes in Magpul's increasingly popular MOE forearm, pistolgrip, and stock. Like all LWRC's lineup this rifle is built with quality parts and finish. This rifle is really lightweight at 6.44lbs. For those who want a KISS piston, this is it! Prices are not set, but MSRP may be $1600-$1650.