The SG 551 carbine has a shorter 363 mm (14.3 in) barrel, gas tube and piston compared to the SG 550. The handguards were also changed and the bipod removed. The SG 551 cannot be used with a bayonet or to fire rifle grenades. The SG 551 comes in several specialized variants designed for use with security and special forces. Among those variants are: the SG 551-1P police carbine (designed to engage point targets out to 300 m, equipped with a Hensoldt 6x42 BL telescopic sight and detachable cheek riser), the SG 551 SWAT carbine (coated with a corrosion-resistant finish and equipped with an optical sight, for example Trijicon's ACOG 3.5x35; this variant can also accept mission-critical accessories such as a bipod, laser pointer or tactical light) and the SG 551 LB carbine with an extended barrel 454 mm (17.9 in) that enables the use of rifle grenades.