Complete AR-15 rifle build kits chambered in 300 Blackout (300 AAC) — the round designed to run in a standard AR-15 using the same lower and magazines as 5.56, so you only change the upper/barrel. Each kit includes a barreled 16″ upper assembly, handguard, bolt carrier group, charging handle, gas system, buffer tube, stock, grip, and lower parts kit. Kits ship with an 80% lower or without a lower; some are unassembled. No magazine or sights included. Filter by handguard, finish, and configuration.

AR-15 300 Blackout Rifle Build Kits

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Choosing a 300 Blackout Build Kit

300 Blackout was built to give the AR-15 more punch from a short barrel and to run quiet with a suppressor, all on the standard AR-15 platform. Here's what to weigh.

With or without an 80% lower

"With 80% lower" kits include an unfinished lower so you have the whole build; "no lower" kits include everything except the lower. The product title says which, and whether the upper ships assembled or unassembled.

What's in the kit

A barreled upper (4150 chrome-moly barrel, M4 feed ramps, free-float Keymod or M-LOK handguard, muzzle device, BCG, charging handle, gas block and tube), plus a buffer tube, stock, grip, and lower parts kit. No magazine, no sights. Exact contents vary by kit — check the listing.

Why 300 Blackout

300 BLK uses the same bolt face, lower, and magazines as 5.56 — only the barrel/upper differ — so it's an easy second upper for an existing AR-15. It delivers more energy than 5.56 from short barrels and runs well subsonic and suppressed, making it a favorite for SBR, pistol, and hunting builds.

Frequently Asked Questions

Does 300 Blackout use the same lower and magazines as 5.56?

Yes. 300 Blackout runs on a standard AR-15 lower, bolt carrier group, and standard 5.56 magazines — only the barrel/upper is caliber-specific. (Keep 300 BLK and 5.56 ammo clearly separated, since 300 BLK can chamber in a 5.56 barrel with dangerous results.)

Do these kits include a magazine or sights?

No. The kit is the major rifle components only — add your own magazine and sighting system.

With lower vs no lower — what's the difference?

"With 80% lower" includes an unfinished lower; "no lower" includes everything else. Choose based on whether you already have a lower.

Do you need an FFL to buy a rifle build kit?

It depends on how a kit is configured and where you live, and the rules continue to evolve. Confirm current federal and state requirements and how a specific kit ships before ordering. This is general information, not legal advice.