The evolution of the SIG556 platform, the SIG556xi provides shooters with unparalleled modularity in barrel length, caliber, magazine type, and stock configuration. Utilizing the time-tested rotating bolt and adjustable gas piston operating system, the SIG556xi system allows operators a choice of caliber, barrel length, handguard/stock configurations and lower receivers. A removable barrel allows the operator to select the necessary length for a given mission. Adding the appropriate bolt, the SIG556xi can be changed to any of three calibers, 5.56x45mm NATO, 300 Blackout, and 7.62x39mm NATO. Users can also quickly change out the non-serialized lower receiver, allowing the use of either AR-style STANAG magazines or rock-and-lock AK-style magazines. The SIG556xi upper receiver is the serialized part, making the lower an easy to purchase part. Polymer handguards accept all Magpul light and rail kits and the aluminum and carbon fiber handguards accept 2", 4", and 6" M1913 rails. Truly ambidextrous, the SIG556xi features an ambi safety selector, magazine release, and user swappable charging handle (right- or left-handed).
The P556xi is the pistol configuration of the 556xi that's ATF compliant. SIG's SB15 Stabilizing Brace ensures improved accuracy and reduced recoil compared to other AR-style pistols. The unique design uses the forearm to provide a natural and comfortable rest for shooters of all sizes and physical ability. The AK SWAT variant comes chambered for 7.62x39mm rounds. Locking flip-up front and rear sights are included.