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300 Blackout Upper

300 Blackout Upper

Originally developed as a do-it-all whisper cartridge for U.S. Special Operations, .300 AAC Blackout has quickly become a popular choice in caliber among AR-15 builders and owners. Serving you with our commitment to quality and accuracy, we’re excited to offer top-of-the-line 300 BLK uppers for the AR platform.

Upper Configurations and Features

Each of our rifle and pistol uppers ship ready to fire out of the box. All .300 BLK uppers we sell come with top-tier and mil-spec specifications and features:

  • Barrels made exclusively from 4150 CMV or 416R stainless
  • Quality parkerized or Melonite (nitride) protective coatings
  • All upper receivers made from forged (7075-T6) aluminum
  • Standard Picatinny/M1913 rail system for optics and sights
  • Includes HPT/MPI-tested M16 bolt carrier group w/ handle
  • Configured with pistol gas systems to ensure subsonic reliability

300 Blackout & 5.56 Platform Compatibility

Already own an AR-15 chambered in 5.56 or .223? You can swap your complete upper assembly for one chambered in 300 BLK and hit the range! Your existing lower receiver and buffer assembly, bolt carrier group, and even your standard magazines are compatible with 300 BLK cartridges, no modification required. If you elect to build your new rifle or pistol using an 80% lower receiver, rest assured the fabrication process and assembly processes are the same: Both platforms utilize the same specifications and lower parts, and thus require the same jig and tooling to cut and drill the receiver blank.

Building Your Custom .300 BLK AR-15

Want to build your suppressed shooter from scratch? Check out our complete 300 Blackout Build Kits. Each kit includes a ready-to-fire upper, 80% lower of your choice (forged or billet), mil-spec lower parts kit, buffer assembly with six-position M4 buttstock, and all the same specs as our standalone uppers.

Build the perfect configuration without the guesswork: Read our 300 Blackout AR-15 Build Guide here. Our guide covers gas systems, twist rate, barrel length, reliably cycling supersonic and subsonic loads, and we cover ballistics and performance.

Your build awaits you.

DISCLAIMER: If you are new to the world of DIY gun building, you likely have a lot of questions and rightfully so. It’s an area that has a lot of questions that, without the correct answers, could have some serious implications. At 80-lower.com, we are by no means providing this content on our website to serve as legal advice or legal counsel. We encourage each and every builder to perform their own research around their respective State laws as well as educating themselves on the Federal laws. When performing your own research, please be sure that you are getting your information from a reliable source.

We are a national retailer of individual components and not all products depicted on this website are legal in every state. Shipping of various products found on this website are prohibited to some states (such as California, Connecticut, District of Columbia, Hawaii, New Jersey, New York, Rhode Island, and Washington). The information, pictures, text or products presented on this website are not a representation by us, and should not be understood by you, that any product or completed firearm is legal to assemble or own in your state of residence. We encourage each and every builder to perform their own research about the state and federal laws that apply to them. It is your responsibility to understand the law and we encourage you to consult with an attorney or your local ATF representative.