Caliber guide
One Horse · 6-minute read
Same AR-15 platform, two different jobs. Here’s how 300 Blackout vs 5.56/.223 compares on barrel length, suppressors and price, using the One Horse lineup.
Both run on the same AR-15 lower and the same M16 bolt carrier group. Only the barrel, muzzle thread and suppressor change. Pick .300 BLK for a 7.5″ or 10.5″ pistol or a suppressed build with the Ryn. Pick 5.56/.223 for a 16″ rifle, easy-to-find ammo and the lighter Ashe. Never load .300 BLK in a 5.56/.223 chamber. Is your rifle 5.56 NATO or .223? See .223 vs 5.56. For cans: 300 Blackout suppressor (Ryn), Ashe vs Ryn, or how to buy a suppressor.
Published October 15, 2026 · Updated October 16, 2026 · By One Horse, Brownstown, Indiana
The basics
Both cartridges run in an AR-15. On a One Horse build, the lower receiver and the M16 bolt carrier group are the same for either caliber. Shop the 300 Blackout BCG. What changes is the barrel: .300 BLK uses a .30 caliber bore and a 5/8×24 muzzle thread, and 5.56/.223 uses a .224 bore and a 1/2×28 thread.
.300 BLK is loaded with heavier .30 caliber bullets and is popular for short barrels and suppressor use. 5.56/.223 fires a lighter bullet, and the ammo is widely sold.
Never load .300 BLK in a 5.56/.223 chamber. Mark your magazines and keep the ammo separate.
Side by side
Specs from the One Horse uppers. Prices are live from the store.
| Spec | .300 BLK | 5.56/.223 |
|---|---|---|
| Bullet diameter | .30 caliber (.308 in.) | .224 in. |
| Lower receiver | Standard AR-15 lower | Standard AR-15 lower |
| Bolt carrier group | M16 BCG (listed for 5.56 / .300 BLK) | M16 BCG (listed for 5.56 / .300 BLK) |
| One Horse barrel lengths | 7.5″, 10.5″ and 16″ | 7.5″, 10.5″ and 16″ |
| Twist and gas (our uppers) | 1:7, pistol-length gas on 7.5″, 10.5″ and 16″ | 7.5″ and 10.5″: 1:7, pistol gas. 16″: 1:8, mid-length gas |
| Muzzle thread | 5/8×24 | 1/2×28 |
| One Horse suppressor | Ryn .30 cal titanium $549.99 MSRP | Ashe 5.56/.223 $449.99 MSRP |
| Suppressed pistol package | 10.5″ .300 BLK SD with the Ryn $1,299.99 MSRP | 10.5″ 5.56/.223 SD with the Ashe $1,199.99 MSRP |
| Complete pistol, 7.5″ | $699.99 | $699.99 |
| Complete pistol, 10.5″ | $699.99 | $699.99 |
| 16″ rifle | OH-OG04 $549.99 MSRP | OH-OG01, from $549.99 MSRP |
| Complete upper, 7.5″ | $319.99 MSRP | $319.99 MSRP |
| Complete upper, 10.5″ | $349.99 MSRP | $349.99 MSRP |
| Complete upper, 16″ | $369.99 MSRP | $369.99 MSRP |
Barrel length
One Horse builds both calibers in 7.5″, 10.5″ and 16″. Our .300 BLK uppers all use a 1:7 twist with pistol-length gas, including the 16″. On 5.56/.223, the 7.5″ and 10.5″ uppers use a 1:7 twist with pistol gas, and the 16″ uses a 1:8 twist with mid-length gas.
Planning a short build? Read our guide to short AR-15 uppers, check the 10.5″ upper options and match your buffer with the H1, H2 and H3 buffer chart.
Shopping for a 300 blackout rifle? The 16″ .300 BLK rifle (OH-OG04) has a 1:7 twist, pistol-length gas and a 15″ M-LOK handguard, listed at $549.99 MSRP $699.99.
Suppressors
Both come with a Plan B mount included. Neither is rated for full auto fire. You fill out a 4473 at your dealer before you take one home.
Our take
Can’t decide? Start with one caliber and add a complete upper in the other. Your lower and BCG carry over.
Shop by caliber
SKU: OH-OP04
SKU: OH-OG04
SKU: OH-CU05
SKU: OH-RYN30
SKU: OH-OP03
SKU: OH-OG01
SKU: OH-CU01
SKU: OH-ASHE556
Free shipping on orders of $399 or more. Sold out? Click Notify Me When Available on the product page.
Questions
Both run on the AR-15 platform. The difference is the barrel and the cartridge: .300 BLK fires a .30 caliber bullet, and 5.56/.223 fires a smaller .224 caliber bullet. On One Horse builds, the lower receiver and the M16 bolt carrier group are shared, and the barrel, muzzle thread and suppressor are caliber specific.
Yes. An AR-15 lower works with either caliber. Many owners keep one lower and add a second complete upper. One Horse sells complete uppers in both .300 BLK and 5.56/.223.
Yes. One Horse M16 bolt carrier groups are listed for both 5.56 and .300 BLK.
It’s a common choice for short barrels and suppressed setups. One Horse offers .300 BLK uppers and pistols in 7.5 and 10.5 inch lengths, all with a 1:7 twist and pistol-length gas.
5.56/.223 is the more common choice for a 16 inch rifle. The One Horse 16 inch 5.56 upper has a 1:8 twist and mid-length gas.
The Ryn .30 cal titanium suppressor. On .300 BLK, One Horse pairs only the Ryn. The Ryn is grade 5 titanium, 6.4 oz and 6.7 in. long.
The Ashe 5.56/.223 suppressor: 5.4 oz, 6 in. long, with a 1/2×28 thread. One Horse suppressors come with a Plan B mount included, and they aren’t rated for full auto fire.
No. Never load .300 BLK in a 5.56/.223 chamber or 5.56 in a .300 BLK chamber. Mark your magazines and keep the ammo separate.
Order online and pick your FFL dealer. At the dealer you fill out a 4473 before you take it home. Questions? Email customerservice@theonehorse.com.
Yes, on orders of $399 or more.
American Made · Family Owned · Veteran Owned
Pistols, rifles and complete uppers in .300 BLK and 5.56/.223, made in America.
Federal, state and local laws vary and change, and it is the buyer’s responsibility to follow them. Questions? Call 812-200-0305 or email customerservice@theonehorse.com.
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