5.56 NATO vs .223 Remington
5.56x45mm NATO and .223 Remington look nearly the same and share a bullet diameter, but they aren't identical. Knowing the difference keeps you safe and helps you buy the right ammo for your rifle.
What they are
.223 Remington is a commercial cartridge introduced in the 1960s. 5.56x45mm NATO is the military version adopted for the AR-15/M16 family of rifles. The outside dimensions are nearly the same, but 5.56 NATO is typically loaded to higher pressure, and 5.56 chambers have a longer throat (leade) ahead of the case mouth.
Chamber compatibility
| Rifle chamber marked | .223 Rem ammo | 5.56 NATO ammo |
|---|---|---|
| 5.56 NATO | Generally safe | Yes |
| .223 Wylde | Yes | Yes (designed for both) |
| .223 Remington only | Yes | Not recommended: pressure can run higher than the chamber is designed for |
Always check what's stamped on your barrel and follow the manufacturer's guidance.
Common bullet weights
| Weight | Typical use |
|---|---|
| 35–50 gr | Light, fast varmint bullets. |
| 55 gr | The most common practice weight. M193-style FMJ is a popular, usually affordable loading. |
| 62 gr | M855 / SS109-style "green tip" with a steel penetrator. Some indoor ranges don't allow it. |
| 69–77 gr | Heavier match and open-tip loads (OTM), favored for accuracy at longer ranges. |
Twist rate matters. Heavier, longer bullets need a faster rifling twist to stabilize. A 1:7 or 1:8 barrel handles heavy bullets well. A slower 1:12 barrel may struggle with anything much heavier than 55 grains. A 1:9 barrel is a middle ground. Your barrel's twist rate is usually stamped on it or listed in the specs.
Range ammo vs. defensive and hunting ammo
Practice: FMJ in 55 or 62 grains, brass or steel case. Steel-cased ammo is usually cheaper but can't be reloaded, and some ranges ban it. Defense and hunting: soft points, bonded bullets, and polymer- or hollow-tipped bullets are designed to expand. Hunting laws vary. Some states set minimum calibers or energy levels for big game, so check your state's rules before using .223/5.56 on deer-sized game.
What drives price per round
- Quantity: 500- and 1,000-round cases (or loose bulk packs) usually beat 20-round boxes per round, especially once free-shipping thresholds kick in.
- Loading: Basic 55 gr FMJ is usually the cheapest. Steel-core, match, and expanding bullets cost more.
- Case material: Steel and remanufactured brass usually cost less than new brass.
- Military-surplus and military-spec production: Supply and pricing can swing with military contracts and wider demand.
- Shipping and fees: Rifle ammo is heavy. A low sticker price with expensive shipping can end up costing more than a slightly higher price with free shipping.
Tip: Compare like with like: same bullet weight, same case material, and new vs. remanufactured. A 55 gr steel-cased load and a 77 gr match load aren't the same product, even when they share a caliber.
This guide is general information, not legal or safety advice. Always use ammunition that matches the markings on your firearm's barrel or slide and the manufacturer's recommendations, and follow the laws where you live.