ACI 5.56 NATO 10.3″ M-LOK Upper Receiver Assembly | U556103ML

Build or upgrade your AR-15 pistol or SBR with the ACI U556103ML 5.56 NATO 10.3″ M-LOK Upper Receiver Assembly. This complete upper receiver assembly is chambered in 5.56mm NATO and features a 10.3-inch barrel paired with an M-LOK compatible handguard, giving you a versatile platform ready for lights, grips, rail sections, and your preferred accessories right out of the box.

Whether you’re putting together a compact home defense build, a range-ready AR pistol, or a registered short-barreled rifle, the ACI U556103ML delivers quality construction and a reliable foundation to build from. The M-LOK handguard keeps your setup lightweight and customizable, while the 5.56 NATO chambering ensures broad ammunition compatibility.

At Deep Roots Rifle Co, we carry hard-to-find upper assemblies like this one so your build doesn’t have to wait. Our knowledgeable staff can help you pair this upper with the right lower receiver, bolt carrier group, or charging handle to complete your setup. Order online at deeprootsrifleco.com for fast shipping nationwide, or visit our gun store in Eustis, Florida for hands-on expert guidance. Competitive pricing, real inventory, and a team that knows AR builds inside and out — that’s the Deep Roots difference.