The SG 551 series 1 was introduced for police, military and sniper use just before the end of the millenium. The Series 2 was released last year to take advantage of the changing technologies and to offer a new weapon instead of an ever-increasing line of upgrades on the Series 1. Now chambered in the favoured 6.5CL cartridge, the Series 2 sports an even lighter frame assembly, a 1.5x to 10x (or to 20x for the sniper edition) electronic scope with Low Lite and Thermo Imaging, folding stock, and underbarrel lug (for bayonets, flashlights, laser sights or bipods).