5.56 NATO vs .223 Remington: what SAAMI and Hornady say
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Guide reviewed 2026-10-09. Safety statements below are the publishers' own words, quoted and linked. Follow your firearm manufacturer's manual.
What SAAMI says
SAAMI, the industry standards body, answers whether the two are interchangeable:
"It is safe to shoot 223 Remington ammunition in a 5.56 military specification chamber."
"However, it is not safe to shoot '5.56,' '5.56 NATO,' or '5.56x45mm' ammunition in a barrel marked as being chambered in 223 Remington for a number of reasons. The main reason being that a barrel marked as chambered in 223 Remington will have a shorter throat into the rifling than a '5.56' barrel which may cause increased pressure if the '5.56' ammunition is fired in it."
SAAMI also notes that, because many "wildcat" or non-military 5.56 chamber shapes exist, you should consult the firearm owner's manual or the manufacturer about whether a given firearm can safely shoot .223 Remington.
Pressure and chamber, per Hornady
- Hornady states that 5.56 NATO "runs at approximately 58,000 psi" and a .223 Remington "is loaded to approximately 55,000 psi."
- It states a 5.56 NATO chamber has a ".125 inch longer throat."
- It states that firing 5.56 NATO in a .223 chamber "will cause a 223 chambered weapon to run at approximately 65,000 psi or more."
- In the other direction, it states a .223 Remington cartridge "may not work optimally" in a 5.56 NATO chamber, and that problems start with a 14.5 inch or shorter barrel.
SAAMI publishes the cartridge and chamber dimensions and pressure limits for U.S. commercial ammunition in its Z299.4 standard for centerfire rifle cartridges, listed on its standards page. This guide does not restate figures from a NATO specification, because that document was not available to read for this review.
How this site lists them
RangeRegistry files .223 Remington and 5.56 NATO ammunition together on one page, .223 / 5.56. Each row keeps the merchant's own title, so read the cartridge name on the row before buying and match it to the marking on your barrel.
Of the 1565 rows on that page right now, 462 name 5.56 only, 1085 name .223 only, 18 name both, and 0 name neither in the title. This count reads the listing title and nothing else.
Median price per round by title: 5.56 only $0.70/rd (462 listings), .223 only $1.00/rd (1085 listings).
Cheapest right now
- .223 / 5.56: $0.44/rd at Freedom Munitions. Buy at Freedom Munitions
Sources
Where this comes from.
Sources were opened and read on or before . Quotes are the publisher's own words; the page may have changed since.
- SAAMI: Frequently asked questions (.223 Remington and 5.56 interchangeability)
- Hornady Law Enforcement: difference between 5.56 NATO and 223 Rem
- SAAMI: ANSI/SAAMI standards (lists Z299.1 rimfire, Z299.3 pistol and revolver, Z299.4 centerfire rifle)
Buyer's guides