SIG Sauer SIG551A1 5.56mm NATO Semi-Auto Rifle, Swiss Gray, 16.3 in CHF 1/7 Threaded Barrel, Diopter Sights, Side-Folding Stock (2011–2012)
This U.S.-made SIG551-A1 is a short-run 2011–2012 production rifle marked SIG SAUER INC., Exeter, NH, finished in Swiss gray, and built around the classic 55X pattern. It features a cold hammer forged 16.3 in barrel threaded 1/2x28 with a SIG 55X-style closed-tip 3‑prong flash hider, a two-position adjustable gas valve, and factory rotary diopter sights. A receiver-top full-length Picatinny rail, side-folding polymer skeleton stock, and compatibility with SIG 55X translucent magazines round out a feature set sought after by 55X enthusiasts.
Condition
Overall Condition: Very good condition, showing only light, superficial signs of prior handling or use.
Bore Condition: Excellent - Clean, mirror finish, no signs of wear.
Bore Rifling: Excellent Rifling - Sharp lands and grooves.
Specific Condition Notes: This rifle is in great shape with minor, superficial scratches and small handling blemishes. The bore is clean and shiny.
What’s Included
- SIG Sauer hard rifle case
- Original manual
- 1x 20-round SIG 55X-pattern translucent polymer magazine with integral coupling lugs and witness marks
U.S. production for the SIG551-A1 ran from 2011 to 2012, and this example carries the SIG SAUER INC., Exeter, NH marking and the distinctive Swiss gray finish. It follows the 55X layout with a 551-pattern two-piece polymer handguard and a side-folding, skeletonized polymer stock for compact storage.
The 16.3 in cold hammer forged barrel is marked 5.56 NATO 1/7 P, is threaded 1/2x28, and comes with a SIG 55X-style closed-tip 3‑prong flash hider installed. The 1:7 twist supports a broad range of 5.56mm NATO projectiles, and the barrel is complemented by a bayonet lug under the gas block.
Its operating system is a semi-automatic, long-stroke gas piston with a rotating bolt, paired with a two-position adjustable gas valve (normal/adverse) for tuning across conditions. A factory bolt-catch lever and paddle-style magazine release are included, along with a manual safety.
Target-focused sights include a protected front post and a rotary diopter rear mounted on the receiver rail. The top of the receiver features a full-length Picatinny rail, and the rifle accepts SIG 55X translucent magazines with coupling lugs. Capacity is 20+1 with the included 20-round magazine, and the length of pull measures 13.0.