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Obtain maximum subsonic and supersonic accuracy with a 300 Blackout AR rifle kit.

Most shooters build 300 Blackout AR pistols, since the .300 AAC Blackout cartridge's subsonic loads can obtain good accuracy with a barrel as short as 10.5". But if you want to enjoy subsonic suppression and maximum supersonic accuracy, it makes perfect sense to invest in a 16"-barreled setup like the kits you see above. 

Why a 16" Barrel for 300 Blackout

Ballistics testing has shown that when a 125-grain 300 Blackout cartridge is fired from a 16" barrel, it obtains the same amount of energy at 700 meters as a 5.56 NATO cartridge at 500 meters. Most agree with this barrel length, the effective range of the round is increased dramatically. Based on hit probability, the effective range is improved to 460 meters, from less than 300 meters using a pistol-length barrel. With a 16" barrel, your 300 BLK AR is also legally configured a rifle and can utilize a standard buttstock for improved comfort and accuracy.

Can subsonic ammo still run in a 16" Barrel?

Yes. Even with a 16" barrel, subsonic 300 BLK loads will retain a muzzle velocity less than 1,125 FPS - that's the transonic sound barrier. Anything below this velocity will provide excellent suppressed sound reduction by avoiding that telltale supersonic "crack" downrange. And with a 16" barrel, you'll obtain maximum gyroscopic stability of those heavy sub loads, affording greater accuracy compared to a shorter barrel.

Why our 300 BLK Rifle Kits

  • All carbon barrels forged from MIL-B-11595 E steel (4150 or Chromoly Vanadium).
  • All carbon barrels and chambers treated with Nitride (Melonite) or Phosphate coating.
  • All stainless / match barrels forged from Crucible 416R steel for sub-MOA accuracy.
  • All bolt carrier groups (BCGs) are full-auto/M16 in profile, staked, and chrome-lined.
  • All upper receivers are forged from mil-spec 7075-T6 aluminum with M4 feed ramps.
  • All buffer assemblies and lower parts kits are mil-spec in fit and finish.

Assembling your AR-15 in 300 BLK

The upper receiver assembly in your kit ships fully assembled and ready to fire once paired with a functional lower assembly. We include all parts required to build your lower assembly, minus the lower receiver itself. You can utilize a stripped lower purchased from an FFL, or you can fabricate your own receiver from an AR-15 80% lower (restricted in some states)! The 300 Blackout platform uses standard AR-15 parts. Be sure to grab an AR-15 jig to fabricate your lower.

Want to know more? Read our in-depth 300 Blackout Guide.

State Laws Vary

These 300 Blackout rifle kits do not include a stripped lower receiver and no components contained in the kits are considered firearms under federal law. Some states have still banned certain firearm parts and kits like these, and we cannot ship such kits to those states. Check our Shipping & Returns page before ordering to make sure your kit can be shipped. 


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, 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.