SIG Sauer SIG556xi 5.56 NATO Semi-Auto Rifle, 16 in Barrel, Long-Stroke Piston, KeyMod Handguard, Side-Folding Stock
This SIG Sauer SIG556xi stands out for its modular, multi-caliber design, serialized upper receiver, and Swiss-inspired ergonomics. It features a 16 in barrel with an open two-prong flash hider, an adjustable gas regulator, and a free-float aluminum KeyMod forend with a continuous 1913 top rail that bridges the receiver and handguard. The model was discontinued after a short production run, adding context for buyers who value limited-production variants.
Condition
Overall Condition: Very good condition, showing only light, superficial signs of prior handling or use.
Bore Overall Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
Specific Condition Notes: This firearm is in great shape. There are some minor and superficial scratches and blemishes present. The bore is clean and shiny.
What's Included
- 1x 30-round CAA Command Arms CD MAG polymer AR-15 pattern magazine
The SIG556xi uses a gas-operated, long-stroke piston system with an adjustable gas regulator at the gas block. Chambered in 5.56mm NATO, it accepts STANAG/AR-15 pattern magazines and includes an open two-prong flash hider on its 16 in barrel. There are no iron sights installed.
Control layout is modern and flexible: the rifle has an ambidextrous magazine release and an ambidextrous manual safety selector. The side charging handle is reciprocating, reversible, and currently installed on the right side.
The rifle’s modularity is a key hallmark of the SIG556xi series. The upper receiver is the serialized component and is marked "SIG556XI" and "MULTI-CAL" with the SIG SAUER, INC., EXETER, NH, USA manufacturer line. This multi-caliber architecture was a defining feature of the short-run series.
Forend and mounting surfaces are well-executed. The free-float aluminum KeyMod handguard helps keep weight forward under control and supports accessory mounting, while the continuous 1913 top rail bridges the receiver and handguard. A Swiss-style side-folding, non-telescoping polymer stock offers compact storage with a 13.0 length of pull.