From the Sig Sauer website:
TACTICAL PRECISION, For 2011, SIG SAUER® is offering several variants to its tactical platforms. Leading the way is our new SIG556 Russian, chambered for the widely used 7.62 x 39mm caliber. Using AK-type magazines, the shooter now has a more potent round for small to medium game. The SIG556R features a distinctive folding and telescopic stock, and an M1913 rail for accessory attachment. The 16” barrel features four-groove rifling and a twist rate of 1:9.5”. At its full extension, the SIG556R measures 36” but can fold to 26”, making it ideal for situations where maximum maneuverability is required. For Special Forces requiring an accurate, more potent rifle, chambered in 7.62x39mm, the SIG556R sets a new standard for dependable
operation and function.