AR-15 pistol build kits chambered in 300 Blackout — the caliber purpose-built for short barrels, which makes it a natural fit for a 300 Blackout pistol (often called an ARP, short for AR pistol). Each kit is built around a short barreled 300 Blackout upper (commonly 7.5″ or 10.5″) with handguard, gas block, muzzle device, BCG, charging handle, pistol buffer setup, grip, and lower parts kit, available with an 80% lower or without a lower. Runs on standard AR mags. No brace or sights included. Filter by barrel length and finish.

AR-15 300 Blackout Pistol Build Kits

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Choosing a 300 Blackout Pistol Kit

300 Blackout was designed to perform from short barrels, so it loses far less than 5.56 in a pistol-length build — and it runs on the standard AR platform. Here's what to weigh.

With or without an 80% lower

"With 80% lower" kits include an unfinished lower; "no lower" kits include everything except the lower. The title says which, and whether the upper ships assembled.

What's in the kit

A short barreled upper (chrome-moly barrel, handguard, gas block, muzzle device, BCG, charging handle), pistol buffer parts, grip, and lower parts kit. "With lower" kits add an 80% lower. No brace, no sights. Contents vary by kit — check the listing.

 Why 300 Blackout in a pistol

300 BLK reaches near-full velocity from a 7.5"–10.5" barrel, where 5.56 falls off sharply, so you get more energy from a compact package. It uses the same lower, bolt, and magazines as 5.56 — only the barrel/upper differ — and runs well subsonic and suppressed, a popular pairing for short builds.  Because only the 300 Blackout upper changes, you can build a 300 Blackout pistol on a lower you already own, or swap between a 5.56 upper and a 300 Blackout upper on the same lower.

Frequently Asked Questions

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

Yes — standard AR-15 lower, BCG, and 5.56 magazines; only the barrel/upper is caliber-specific. Keep 300 BLK and 5.56 ammo separated, since 300 BLK can chamber in a 5.56 barrel with dangerous results.

Do these kits include a brace or sights?

No. Add a brace and sighting system separately to fit your build and current regulations.

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

"With 80% lower" includes an unfinished lower; "no lower" includes everything else.

Are 300 blackout AR pistols legal / do you need an FFL?

It depends on configuration and where you live, and the rules around AR pistols, braces, and unfinished receivers have changed and continue to evolve. Confirm current federal and state law and how a specific kit ships before ordering. General information, not legal advice.

What does ARP mean for an AR pistol build?

ARP is shorthand for AR pistol — an AR-15 or AR-10 pattern build without a shoulder stock, built on a pistol brace or bare buffer tube instead. A 300 Blackout ARP pairs that pistol format with the 300 Blackout cartridge specifically because the caliber holds its velocity in the shorter barrel lengths (7.5″–10.5″) that ARP builds typically use.

What makes a good barrel length for 300 Blackout pistol ?

Most 300 Blackout pistol builds run 7.5″ or 10.5″ barrels — short enough to stay in pistol-length territory, long enough to keep the cartridge's ballistics intact. The 7.5″ is the more compact option; the 10.5″ gives up a little size for slightly more velocity and a longer sight radius. Either works well suppressed or unsuppressed.