The SR9s are modified HK91-series rifles intended to qualify for import as sporting rilfes 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".
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 Sept. 1994 were sold with a 5-round magazine because of the US Federal ban on high capacity mags.
The SR9-series rifles have unreinforced receivers fitted with iron sights and semiautomatic-only trigger group. The safety is thumb operated on the left side of the receiver. The cocking handle is forward on the left, as in the rest of the G3 family, and folds flat. The magazine release is a push button only from the right side of the receiver.
The forearm is a sure-grip style new to this model which precludes the attachment of a bipod. It is, howver, replaceable with standard HK91 furniture. The barrel has the same bore profile as the PSG1, including polygonal rifling, and lacks a muzzle device. The basic SR9 is fitted with a reinforced fiberglass thumbhole stock containing an MSG90 buffer.
- SR9 T (Target): differs from the basic SR9 by replacing the thumbhole buttstock with the adjustable buttstock from the MSG90. The MSG90 buttstock makes use of the iron sights awkwark because of the raised cheek piece. Additionally, the PSG1 precision trigger group and a contoured adjustable handgrip are fitted.
- SR9 TC (Target Competition): differs from the SR9T in that it has a PSG1 "club-foot" adjustable buttstock. The rear iron sight is useless since the adjustable cheek piece of the PSG1 stock places the shooter's head too high to use the sights. The PSG1 sniper trigger group and stippled walnut handgrip is the same as on the SR9T.