Model Variants (Including Prototypes)
SG 550 - Swiss Designation; base production model.
SG 551 - Carbine based on the full-length SG 550; 14.3-inch barrel; revised handguard; sans bipod; sans support for rifle grenades and bayonet.
SG 551-1P - Police version of SG 551
SG 551 "SWAT" - SWAT version of SG 551
SG 551 LB ("Long Barrel") - 17.9-inch barrel; support for rifle grenades and bayonet.
SG 552 "Commando" - Compact Carbine Form; 8.9-inch barrel; reworked internals; appearing in 1998.
SG 552-2P - Police bersion of SG 552 Commando
SG 552 LB ("Long Barrel") - Variant of SG 552 with 13.6-inch barrel; compatible with rifle grenades and bayonet.
SG 553 - Improved SG 552; internals follow SG 550 models; 13.3-inch barrel; appearing in 2009.
SG 553 LB ("Long Barrel") - 13.7-inch barrel; Picatinny rail; support for rifle grenades and bayonet.
SG 550 "Sniper" - Dedicated marksman rifle form; two-stage trigger; 25.6-inch heavy barrel; sans iron sights; 5- or 20-round magazine; bipod; adjustable shoulder stock; new ergonomic pistol grip.
Fass 90 - French Army Designation of SG 550
Stgw 90 - German Army Designation of SG 550
SG 550 "Sport" - Civilian Rifle Form
SIG 556 - American Commercial Market Variant
SIG 522LR - Chambered for the .22 cartridge; blowback operation.
SG 550 SP - Civilian version of SG 550; semi-automatic fire only.
SG 551 SP - Civilian version of SG 551; semi-automatic fire only.
SG 552 SP - Civilian version of SG 552; semi-automatic fire only.
SIG556 "Classic" - Slim profile variant; Picatinny rail.
SIG556 DMR - 21-inch barrel; Magpul stock.
SIGP556 - Pistol Variantl 10-inch barrel