The SR9s are modified HK91-series rifles intended to qualify for import as sporting rifles after the US ban on imported assault rifles in 1989. The visible differences include the removal of the flash suppressor, bayonet lugs, and pistol grip (on the base model) in order to improve the design’s acceptance as a sporting rifle. The SR9s have a medium weight barrel that is slightly less than 20 inches. Internal differences include a new buffer system and a change to polygonal rifling.
All SR9s are marked “Made in W-Germany” on the right side of the receiver. SR9s imported after September 1994 were sold with a 5-round magazine because of the US Federal ban on ‘high-capacity magazines’ (magazines capable of holding more than 10 rounds).