This Geissele SD-556 features an adjustable support brace, a threaded barrel with muzzle brake, and a Primary Arms ACSS G2 Cyclops micro prism optic. Purchase includes the original box, manual, and one 30-round magazine. Get the best bang for your buck when you get a Certified Used Firearm. When you see the Certified Used stamp on any of our firearms, you can be confident that you're getting exactly what you want - a gun only in very good to excellent condition and held to the highest quality standard. All Certified Used Guns come with a 'no questions asked' return policy.