SIG 556

SIG 556 semi-automatic rifle,left side; buttstock collapsed.
SIG 556 semi-automatic rifle, left side, (buttstock collapsed).

SIG 556 semi-automatic rifle,right side.
SIG 556 semi-automatic rifle, right side.


Type / action semi-automatic rifle,gas-operated
Caliber(s)  .223Remington (5.56×45)
Weight unloaded 3.54 kg/ 7.8 lbs
Length 940 mm / 37″
Barrel length 406 mm/ 16″
Magazine capacity 30 rounds



The SIG 556 semi-automatic rifle was announced in 2006 as a rifle for civilian and law-enforcement use. It was produced by international SIGARMS (now SIG Sauer arms corporation) and intended primarily for the US market. The SIG 556 is based on the SIG SG 550 assault rifle, still in use by the Swiss army today. In the Swiss Army, it is designated as ‘Stgw 90’ or ‘Sturmgewehr 90’ (‘SG’ also refers to the word ‘Sturmgewehr’). It’s limited to semi-automatic fire only, thus being legal in most countries that permit civilians to own rifles. SIG Sauer also produces a SIG 556 SWAT semi-automatic rifle which has a different butt stock and a 4-rail forend.


The SIG 556 semi-automatic rifle is gas operated, using a short-stroke gas piston located above the barrel. The gas system has a manual gas regulator with two settings, either for normal or harsh conditions. The barrel is locked using a rotary bolt with two massive lugs. The receiver is redesigned from the original SIG SG 550 rifle, and features a stamped steel upper part mated to an aluminum alloy  lower part. The lower houses a trigger unit and a redesigned magazine accepting all M16 / Ar-15 type magazines. A bolt stop device is incorporated into the design. The manual safety is ambidextrous and located above the pistol grip. The rifle is shipped with a standard 30-round magazine. In it’s basic configuration SIG 556 has no iron sights (adjustable folding ironsights are an optional extra). The top of the receiver is fitted with a Picatinny rail for easy installation of various optical or red-dot sights; additional rails are installed on the forend, at 3-, 6- and 9-o’clock positions. The Buttstock is of a non-folding, telescoped, adjustable type.