.223 vs 5.56 vs .223 Wylde: What SAAMI's 5.56 COMM Changes

SAAMI accepted 5.56 Commercial, abbreviated 5.56 COMM, as a new rifle cartridge and chamber standard on October 12, 2026, with Hornady Manufacturing named as the company that introduced it. The published specification sets a Maximum Average Pressure of 62,000 psi and an instrumental velocity of 55 grains at 3,400 fps. SAAMI calls it a publicly available consensus standard for commercial practice, measured with the procedures and equipment in its ANSI/SAAMI Z299.4 centerfire rifle standard.

The introduction package carries three pages: a compatibility notice, a cartridge and chamber drawing, and a velocity and pressure test barrel drawing. The package itself is dated June 22, 2026 (Rev. 0) and both drawings show a June 9, 2026 issue date; the public announcement followed in October. Crusher (CUP) pressure limits were not established, so 62,000 psi is a transducer figure.

.223 Remington ammunition is safe in a 5.56 military-specification chamber, and 5.56 ammunition is not safe in a barrel marked .223 Remington. That is SAAMI's standing guidance, and the reason it gives is the throat: a .223 Remington chamber has a shorter throat into the rifling than a 5.56 chamber, which can raise pressure when 5.56 ammunition is fired in it. SAAMI also notes that many non-military 5.56 chamber geometries exist, so it tells owners to confirm with the manual or the firearm maker before assuming a 5.56-marked rifle runs .223 Remington.

.223 Remington is a SAAMI cartridge with a Maximum Average Pressure of 55,000 psi in Z299.4. 5.56 NATO is a military designation, and SAAMI states plainly that no publicly available standard exists for 5.56x45 or 5.56 NATO, so there is no SAAMI pressure figure for 5.56 NATO to set beside .223 Remington's. SAAMI declines to make blanket compatibility statements across that gap, and it tells owners to rely on the barrel marking and the manufacturer instead.

5.56 COMM changes one thing in that picture. For the first time, a cartridge carrying the 5.56 name has a public SAAMI pressure limit, 62,000 psi, measured with the same Z299.4 procedures as .223 Remington's 55,000 psi. For load selection by barrel length and twist, our 5.56 ammo selection guide covers the rest.

The 5.56 COMM chamber drawing specifies a wider throat with a gentler leade than the .223 Remington chamber in Z299.4. The cylindrical throat ahead of the case mouth is .2262 inch in diameter on the 5.56 COMM drawing versus .224 inch on .223 Remington, and the leade angle into the rifling is 1° 13' 20" versus 3° 10' 36". The cartridge drawings themselves are nearly identical: both list a 1.760 inch maximum case length, the same 2.125 to 2.260 inch overall length window, and the same .219 inch bore and .224 inch groove.

The test barrels differ too. SAAMI's .223 Remington velocity and pressure barrel is 24 inches with a 1:12 twist; the 5.56 COMM test barrel is 20 inches with a 1:7 twist. Velocities from the two standards are therefore not a like-for-like comparison, and neither predicts what a 16-inch carbine chronographs.

SAAMI's throat explanation for the .223 Remington warning lines up with these drawings: the chamber drawn for 62,000 psi has a larger-diameter throat with a shallower leade. That is a description of two published drawings, not a measurement of any particular rifle. Commercial 5.56 NATO and .223 Wylde barrels are cut to their makers' reamer specs, which SAAMI does not publish.

.223 Wylde is a hybrid chamber, not a cartridge, and barrel makers cut it to fire both .223 Remington and 5.56 NATO. Faxon Firearms credits its design to competition shooter and gunsmith Bill Wylde and describes it as using 5.56 NATO body dimensions so it accepts both loads, with accuracy potential closer to a .223 Remington chamber. There is no SAAMI .223 Wylde cartridge or chamber; it does not appear in Z299.4, so the barrel maker's documentation is the authority on what a specific Wylde barrel accepts.

For 5.56 COMM ammunition, a .223 Wylde barrel falls under the same instruction as any rifle not marked 5.56 COMM: SAAMI says to contact the firearm or ammunition manufacturer. Our AR-15 barrel guide compares 5.56 NATO and .223 Wylde barrels by contour, gas length, and construction.

It means the rule you already follow is now written for 5.56 COMM too: if the barrel is marked only .223 Remington, feed it only .223 Remington. SAAMI's notice says that guidance "remains unchanged" and lists any 5.56 ammunition, all military variants, and ammunition built to the new standard as unsafe in a .223 Remington chamber.

Read the chamber marking on the barrel itself. If the marking is missing or unclear, ask the barrel or rifle maker before buying ammunition. The table below summarizes what SAAMI's published guidance covers and where it hands the question to the manufacturer.

Buy ammunition labeled for the chamber your barrel is marked for. A .223 Remington load such as PMC Bronze 55 gr is cleared by SAAMI's guidance for both a .223 Remington-only barrel and a 5.56 military-specification chamber. 5.56 NATO loads such as IMI M193 and Hornady BLACK 62 gr belong in 5.56 NATO barrels and in .223 Wylde barrels whose makers approve 5.56 NATO, never in a .223 Remington-only barrel. For how M193 compares with green tip, see M193 vs M855 vs M855A1.

As of October 13, 2026, there is no 5.56 COMM ammunition or rifle announced for sale. SAAMI's announcement and introduction package name no commercial load, rifle, price, or ship date. Hornady's 2027 New Products sell sheet, posted to its media center on October 12, 2026, lists no 5.56 COMM item; its only new 5.56 product is SBR Suppressed 5.56 NATO 73 gr ELD Match (item 81244). What the SAAMI package does list is Hornady as the supplier of 5.56 COMM reference rounds (83678R), dummy rounds (83678D), and proof ammunition (83678P), the support products manufacturers and test labs use to calibrate equipment and proof firearms.

Nothing forces the name onto barrels or boxes either. SAAMI states the standard does not require firearm makers to roll mark guns 5.56 Commercial or 5.56 COMM, and does not require ammunition makers to adopt a 5.56 COMM headstamp, though using the designation is acceptable practice. SAAMI standards are voluntary; the Z299.4 front matter says the use of American National Standards is completely voluntary. Planning a new upper around the chamber question starts in the rifle builder, and the AR-15 caliber guide covers the cartridges beyond .223 and 5.56.