.223 vs 5.56: What Your AR-15 Chamber Can Fire

.223 Remington and 5.56 NATO look alike, but they are not the same. Here is what each chamber can safely fire, and how One Horse uppers are chambered.

Shop complete uppers See the chamber chart

Quick answer

A 5.56 NATO chamber fires both 5.56 NATO and .223 Remington. A .223 Remington chamber is for .223 Remington only: don’t fire 5.56 NATO in it, because 5.56 runs at higher pressure. A .223 Wylde chamber fires both. Check what’s marked on your barrel and buy ammo that matches. One Horse 5.56/.223 uppers are chambered for 5.56 NATO and .223 Rem.

Chamber chart

Which ammo each chamber fires

Chamber marked on barrel	.223 Remington ammo	5.56 NATO ammo	Notes
5.56 NATO	Yes	Yes	The safe, flexible choice. One Horse uppers use it.
.223 Wylde	Yes	Yes	Hybrid with dimensions aimed at accuracy.
.223 Remington	Yes	No	5.56 NATO runs at higher pressure.

One Horse 5.56/.223

Our 5.56/.223 uppers at a glance

Barrel	Twist	Gas	Muzzle thread
7.5″	1:7	Pistol	1/2×28
10.5″	1:7	Pistol	1/2×28
16″	1:8	Mid-length	1/2×28

Every complete upper includes an M16 Black Nitride BCG and a standard charging handle and fits a mil-spec AR-15 lower. Pair it with the Ashe 5.56/.223 suppressor or the Ashe vs Ryn choose guide.

Safety first

Never load .300 BLK in a 5.56/.223 chamber. It can chamber and destroy the rifle.
Mark your magazines and uppers, and keep the ammo separate.

Questions

.223 vs 5.56: FAQ

Is .223 the same as 5.56?

No. The cartridges look alike, but 5.56 NATO runs at higher pressure than .223 Remington. Which ammo you can fire depends on the chamber marked on your barrel.

Can I shoot .223 in a 5.56 AR-15?

Yes. A 5.56 NATO chamber fires both 5.56 NATO and .223 Remington ammo.

Can I shoot 5.56 in a .223 rifle?

Not in a .223 Remington chamber. It is made for .223 Remington ammo only, and 5.56 NATO runs at higher pressure.

What is .223 Wylde?

A hybrid chamber that fires both 5.56 NATO and .223 Remington, with dimensions aimed at accuracy.

What chamber do One Horse uppers use?

One Horse 5.56 rifles, pistols and complete uppers are sold as 5.56/.223, with 5.56 NATO listed on the spec sheet. Our complete uppers are chambered for 5.56 NATO and .223 Rem.

Which One Horse suppressor fits 5.56/.223?

The Ashe 5.56/.223 suppressor: 5.4 oz, 6 in. long, 1/2×28 thread, with a Plan B mount included.

Can I put .300 BLK in a 5.56/.223 rifle?

No. A .300 BLK round can chamber in a 5.56/.223 rifle and destroy it. Mark your magazines and uppers and keep the ammo separate.