Geissele Automatics Super Duty SD-556 5.56 NATO AR-15 Rifle, 16.5" Barrel, MK16 13.5" DDC Rail, REBCG, Pinned 3-Prong Flash Hider
This Geissele Automatics SD-556 Super Duty stands out with a 16.5" barrel capped by an open three-prong flash hider that is pinned and welded, a Geissele REBCG with NanoWeapon-type coating, and the MK16 13.5" DDC handguard marked with NSN 1005-01-672-4797. It features a forged aluminum receiver set, a continuous T-marked Picatinny top rail, and purpose-built controls and furniture with tan accents. Model marking on the receiver confirms SD-556 lineage.
Condition
Overall Condition: Very good condition, showing only light, superficial signs of prior handling or use.
Bore Condition: Good - Clean, well-maintained, minor wear marks.
Bore Rifling: Good Rifling - Intact, well-defined lands and grooves.
Specific Condition Notes: A few scuffs and scratches are present, especially on the charging handle. There is some wear on the polymer furniture. Carbon buildup is visible on the pinned and welded muzzle device. Overall, the rifle is in great shape.
What’s Included
- 1x 30-round Magpul PMAG polymer magazine for 5.56x45 (STANAG pattern)
- Angled foregrip (tan), installed on the M-LOK handguard
- Polymer M-LOK rail panel covers installed on the handguard
- BCM M-LOK QD sling mount, installed
Built on Geissele’s Super Duty platform, this SD-556 is chambered in 5.56mm NATO and uses a semi-automatic, direct impingement system. The barrel measures 16.5" and is topped with an open three-prong flash hider that is pinned and welded. The receiver is marked SD-556, and the rifle is made in the USA.
The handguard is the Geissele Super Modular Rail MK16, 13.5" in DDC, machined from 7000-series aluminum and marked with NSN 1005-01-672-4797. It offers M-LOK attachment slots with a continuous T-marked Picatinny top rail. This example comes equipped with a tan angled foregrip, polymer M-LOK rail covers, and a BCM M-LOK QD sling mount.
Internals include the Geissele REBCG (Reliability Enhanced Bolt Carrier Group) with a NanoWeapon-type coating, and the bolt carrier is marked "GEISSELE." Controls are thoughtfully executed with an enlarged textured bolt catch featuring a right-side bolt release, an ambidextrous manual safety, and a tan-anodized ambidextrous charging handle with extended knurled levers. Tan accents are present on select controls, including the dust cover, and a flat-bow trigger is installed.
Furniture consists of a tan collapsible 6-position polymer stock with a rubber buttpad and a tan textured polymer pistol grip. The rifle retains a threaded barrel, with the barrel device pinned and welded, and offers a 14.25" length of pull. Capacity is 30+1 rounds.