5.56 NATO vs .223 Remington: What's the Difference and Does It Matter?
5.56 NATO and .223 Remington look identical but have important differences in pressure, chamber dimensions, and safety. This guide explains what you need to know to shoot safely and accurately.
5.56 NATO vs .223 Remington: Understanding the Critical Differences
At first glance, 5.56 NATO and .223 Remington appear identical. They use the same bullets, have virtually identical external dimensions, and will chamber in the same guns. But there are important differences in chamber specifications and pressure that affect safety and performance.
Key Differences Comparison
| Specification | 5.56 NATO | .223 Rem |
|---|---|---|
| Max Pressure | Higher (NATO test method; often cited ~62,000 psi) | 55,000 psi (SAAMI) |
| Chamber Specs | Longer throat, larger chamber | Tighter chamber, shorter throat |
| Case Wall | Varies by manufacturer; military brass is often thicker / less internal volume | Varies; commercial brass often has slightly more internal volume |
| Typical Use | Military, defensive, duty | Target, hunting, competition |
| Cost | $0.40-0.60/round | $0.35-0.55/round |
The Pressure Difference
.223 Remington has a SAAMI max average pressure of 55,000 psi, and 5.56 NATO is typically loaded hotter (often cited around ~62,000 psi under NATO test methods). Because the standards differ, treat this as a practical '5.56 is usually higher pressure' guideline—not a perfect one-to-one comparison. This difference becomes dangerous when you fire 5.56 in a .223 chamber.
The .223 chamber has a shorter leade (throat) and tighter dimensions. When you fire a 5.56 round in this tighter chamber, pressure can rise enough to increase the risk of overpressure signs and component damage. This can cause case head separation, blown primers, or in extreme cases, catastrophic failure.
Chamber Types Explained
.223 Remington Chamber: Designed for commercial .223 ammunition. Tighter tolerances for better accuracy. For best safety, stick to .223 Rem ammunition unless your rifle is explicitly marked for 5.56 or .223 Wylde.
5.56 NATO Chamber: Designed for military ammo with safety margins for field conditions. Longer throat, slightly larger chamber. Can safely shoot both 5.56 and .223.
.223 Wylde Chamber: Hybrid design offering the best of both. Safe for 5.56 NATO pressures with accuracy approaching .223 chambers. Increasingly popular in modern AR-15s.
How to Check Your Chamber
Look at your barrel markings. Most barrels are clearly stamped:
- "5.56 NATO" or "5.56 NATO/.223 Rem": Safe for both
- ".223 Wylde": Safe for both, optimized for accuracy
- ".223 Rem" or ".223 ONLY": .223 Remington only
If you're unsure, contact the manufacturer. Don't guess—it's not worth the risk.
Practical Shooting Considerations
For AR-15 Owners: Most modern AR-15s are chambered in 5.56 NATO or .223 Wylde, meaning you can shoot both safely. Check your barrel markings to confirm.
For Bolt-Action Owners: Many bolt-action rifles are chambered in .223 Remington for maximum accuracy. Stick to .223 ammunition unless your rifle is specifically marked for 5.56.
For Accuracy: If you're shooting precision .223 rifles for competition or varmint hunting, .223 Rem ammunition in a .223 chamber typically offers the best accuracy. For AR-15s with 5.56 or Wylde chambers, both work well.
Ammunition Selection
Defensive/Duty Use: 5.56 NATO ammunition is designed for this. Choose quality defensive loads like Federal Tactical, Hornady TAP, or IMI Razor Core.
Target/Practice: Either works fine. .223 Rem is often slightly cheaper and plenty accurate for practice.
Precision/Competition: Match-grade .223 Rem like Federal Gold Medal, Hornady Match, or Black Hills offers excellent accuracy.
Frequently Asked Questions
Can I shoot 5.56 in a .223 chamber?
NOT RECOMMENDED. While it will chamber, 5.56 ammunition can generate higher pressure in a .223 Rem chamber, especially due to the shorter leade/freebore, which increases risk. Always check your barrel markings. If it says '.223 Rem only', stick to .223. If it says '5.56 NATO' or '.223 Wylde', you can shoot both safely.
Can I shoot .223 in a 5.56 chamber?
Yes, completely safe. .223 Rem has lower pressure and will work fine in 5.56 NATO chambers. You may notice slightly less accuracy due to the longer throat, but it's perfectly safe.
What is .223 Wylde?
.223 Wylde is a hybrid chamber designed to safely shoot both 5.56 NATO and .223 Rem with optimal accuracy. It combines 5.56's safety margin with .223's accuracy potential. Many modern AR-15s use Wylde chambers.
Which is more accurate?
.223 Rem typically offers slightly better accuracy in match-grade .223 chambers due to tighter tolerances. However, quality 5.56 chambers with good ammo are plenty accurate for most uses. For precision shooting under 600 yards, the difference is minimal with quality barrels.
Safety First
Always check your barrel markings before purchasing ammunition. When in doubt, use .223 Remington—it's safe in all chambers. Never fire 5.56 NATO in a rifle marked ".223 Rem only" or ".223 Remington". The few dollars saved on ammunition isn't worth risking your safety or your rifle.
Bottom Line
For most AR-15 owners, this distinction is simple: your rifle is likely chambered in 5.56 NATO or .223 Wylde, so you can safely shoot both. Always verify your chamber markings, and when building or buying an AR-15, consider .223 Wylde for the best combination of safety and accuracy.