The Sig Arms 550/551 Assault Rifles
Caliber: 5.56 NATO (.223rem)
Action: Gas operated, rotating bolt
Overall length: Sig550 1000 mm; Sig551 825 mm
Barrel length: Sig550 533mm; Sig551 405 mm
Weigth with empty magazine: Sig550 4.08 kg; Sig551 3.5 kg
Magazine capacity: 30 rds
Sig 550 was designed by SIG in the early 1980's and was adopted by Swiss military in 1984. Technically, the Sig550 is a gas operated, short stroke, selectable fire weapon, capable of firing in semi-auto, three round bursts and full auto modes. The barrel locking system is somewhat similar to AK-47 (rotating bolt), thus giving it the reliability. The cocking handle is permanently attached to the right side of the bolt. The receiver is stamped from steel, and designed like the M16. The polymer buttstock folds to the right side and is equipped with rubber buttpad.
It is issued with bayonet mount, lightweight folding bipods and clear plastic magazines with built in clips to connect magazines in packs of three.
The Sig551 is a carbine, a shortened version of the standard 550. The differences are only shorter barrel and lack of the bipod and bayonet mount. For law enforcement, the Sig550 and Sig551 are offered in semi-auto only configurations. For special police and law enforcement operations SIG also offered super-short semi-auto version Sig552 "Commando", with barrel length of 254mm.
As any other general issued Swiss weapon, this SIG is extremely accurate in its class, and as reliable as a Swiss watch. It is also reported to be very user-friendly and comfortable to handle.
Works Cited: SIG Arms website and Guns Digest Magazine.