October 15th, 2018

.223 Remington vs. 5.56x45mm — Facts vs. Fiction

.223 Rem Remington 5.56 SAAMI CIP 5.56x45 5.56x45mm NATO cartridge ammo pressure test luckygunner ultimatereloader Gavin Gear

Probably the most popular centerfire rifle round in the Western Hemisphere is the .223 Remington and its metric match, the 5.56x45mm. Though many folks use “.223 Rem” and “5.56×45″ interchangeably, there are some meaningful differences in specifications for the original .223 Rem and the 5.56x45mm cartridge, as adopted by the U.S. military and NATO armies. The default chamber throats are slightly different and the .223 Rem is rated at 55,000 PSI vs. 62,366 PSI for the 5.56x45mm.*

.223 Rem vs 5.56x45mm — Key Differences
There is a truly outstanding, very thorough article on the subject, published by LuckyGunner.com.** This involved extensive testing, with pressure monitors, of 5.56x45mm ammo in .223 Rem chambers. Those tests revealed the peak pressures. Here is one of the ammo test charts:

.223 Rem Remington 5.56 SAAMI CIP 5.56x45 5.56x45mm NATO cartridge ammo pressure test luckygunner ultimatereloader Gavin Gear

NOTE: “The observed chamber pressure for Federal XM855 5.56mm ammunition in a .223 Rem chamber exceeded .223 maximum pressures, but not by a massive amount. The ninth shot (the red line) was an underpowered cartridge which exhibited significantly lower velocity and pressure than the other rounds, so it was excluded from the average velocity and pressure numbers for this chamber.”

And if you’re curious, LuckyGunner also fired .223 Rem ammo in a 5.56x45mm NATO-chambered AR15 rifle. As you would expect, the peak pressures were significantly lower, but the .223 Rem ammo still cycled the semi-auto AR-platform rifle perfectly well:

.223 Rem Remington 5.56 SAAMI CIP 5.56x45 5.56x45mm NATO cartridge ammo pressure test luckygunner ultimatereloader Gavin Gear

READ FULL LuckyGunner .223 Rem vs. 5.56x45mm ARTICLE »

UltimateReloader.com Explains .223 Rem vs. 5.56x45mm
To explain the key differences between the .223 Rem and 5.56x45mm cartridges our friend Gavin Gear of UltimateReloader.com has created a very thorough 12-minute video. This covers the cartridge specifications and explains key considerations for hand-loaders. Gavin also addresses the oft-asked question “Can I shoot 5.56x45mm ammo in my .223 Rem chamber?” Gavin’s video is definitely worth watching. In fact, this is one of the most popular videos Gavin has ever created — it has been watched over 300,000 times on YouTube.

What Exactly Is the 5.56x45mm NATO Cartridge?
The 5.56×45mm NATO is a rimless bottle-necked intermediate cartridge family standardized by NATO with development work by FN Herstal. It consists of the SS109, SS110, and SS111 cartridges. Under STANAG 4172, it is a standard cartridge for NATO forces as well as many non-NATO countries.

Bullet diameter: 5.70 mm (0.224 in)
Maximum pressure (EPVAT): 430.00 MPa (62,366 psi)
Maximum pressure (SCATP 5.56): 380.00 MPa (55,114 psi)
Case length: 44.70 mm (1.760 in)
Rifling twist: 178 mm or 229 mm (1 in 7 in)
Parent case: .223 Remington (M193)

Ammo-Maker Federal Premium Compares .223 Rem and 5.56x45mm
Here is a video from ammo-maker Federal Premium explaining the difference between .223 Remington and 5.56x45mm NATO. Federal states that you may experience excessive pressures when firing a 5.56x45mm in a standard .223 Remington chamber:

One leading gunwriter has addressed the question of shooting 5.56x45mm ammo in .223 Rem chambers. He advocates caution (for more info, SEE pressure tests by LuckyGunner.com):

“I have received a slew of questions — many from first time AR-type rifle buyers — about the .223 Rem and the 5.56×45 mm NATO cartridges. Can I shoot 5.56×45 mm NATO in my .223 and vice-versa? Are these the same cartridge?

Externally, the two cartridge cases are identical. The main differences are that 5.56×45 mm NATO operates at a higher chamber pressure (about 60,000 PSI versus 55,000 PSI on the .223 Rem.) and the 5.56’s chamber is slightly larger than that of the .223 Rem. Also, the throat or leade is longer in the 5.56×45 mm chamber. What does this mean? You should not shoot 5.56×45 mm NATO out of a rifle that is chambered in .223 Rem. And be aware that some .223 Rem. ammunition will not reliably cycle through some AR-style .223 Rem. rifles, but it usually does. As a matter of fact, I have not encountered any difficulty with current .223 Rem. loads cycling through a 5.56 mm AR-style rifle.”
– Mark Keefe, Editor, American Rifleman


* According to the official NATO proofing guidelines, the 5.56×45mm NATO case can handle up to 430.0 MPa (62,366 psi) piezo service pressure. The U.S. SAAMI lists Maximum Average Pressure (MAP) for the .223 Remington cartridge as 55,000 psi (379.2 MPa) piezo pressure with deviation of up to 58,000 psi (399.9 MPa). The chamber for military 5.56×45mm NATO has a longer throat prior to the bullet contacting the rifling which results in lower pressures when firing 5.56×45mm NATO ammunition. If 5.56×45mm NATO is used in rifles chambered for .223 Remington the bullet will be engraving the rifling when chambered. which can increase pressures past SAAMI Max levels. NOTE: The C.I.P. standards for the C.I.P. civilian .223 Remington chamber are much closer to the military 5.56×45mm NATO chamber.

** The full-length LuckyGunner article is well worth reading. It even provides specifications for a number of .223 Rem reamer types, and compares the original .223 Rem, the 5.56x45mm NATO, and the modern .223 Wylde chamberings.

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March 19th, 2013

Mike Walker, Remington Gun Designer, Passes at Age 101

Legendary firearms engineer Merle “Mike” Walker passed away on March 6, at the age of 101. Walker was one of the most important gun and cartridge designers of the 20th Century, and he also was a leading proponent of benchrest shooting. Mike worked for Remington Arms Company for 37 years, as a lead designer and engineer. While at Remington, Mike created many of Remington’s most popular bolt action rifles. For many years, Mike served as Director of Research and head of the Custom Shop at Remington’s, Ilion, NY facility.

Mike Walker Remington

Mike led the development of many important Remington rifle designs, including the Rem m700, Rem 40X, Rem m721, and Rem m722. Walker held numerous patents, mostly for trigger designs.

“Without a doubt, the Remington Model 700 is the most popular commerical, high-power, bolt-action rifle in the world. The Model 700 is actually a product-improved Model 721 and Model 722 bolt-action rifle, the brain-child of Merle ‘Mike’ Walker and his Remington design team in the 1940s.” — Roy C. Marcot, The History of Remington Firearms

Mike was a major pioneer in modern cartridge design — he was the originator of the .222 Remington and the 6mm Remington Int’l rounds. According to Guns & Ammo: “Long-time Remington employee and benchrest competitor Mike Walker, who headed up the M722 design team, is largely credited with the development of the .222 Rem”. The .222 Rem (aka “Triple Deuce”) dominated short-range Benchrest competition until the advent of the PPC cartridges.

Mike Walker

Walker also worked with Jim Steckl on the .30-cal wildcat that eventually evolved into the 6mm Bench Rest Remington. This cartridge demonstrated the accuracy and efficiency of the “short, fat” case design. When brass was eventually produced for the 6mmBR Rem, Mike convinced Remington to produce a run with a small primer pocket. Thanks to these pioneering efforts by Walker and Steckl, we now have the ultra-accurate 6mmBR Norma (with a small primer pocket), and the 30BR wildcat.

Mike was one of the “founding fathers” of the International Benchest Shooters (IBS), and he was in the early IBS leadership group. He was a talented (and dedicated) benchrest shooter. Remarkably, Mike shot in the 2010 IBS Nationals at age 99. Mike also played an key role in the creation of Precision Shooting Magazine. Still engaged in his passion for gun-building and firearm design, he worked in his shop even at the age of 101. He passed in a hospital on March 6, 2013 after hip replacement surgery.

Mike Walker

IBS President Jeff Stover tells us: “The term ‘living legend’ is used in many sports and endeavors. Rarely, though, is that term used as accurately as when referring to Mr. Merle ‘Mike’ Walker. He developed the Rem 700, he helped invent the button rifling process and many other firearms innovations. Probably the last time he shot in competition was at the 2010 IBS Group Nationals at Weikert, Pennsylvania. He got around quite well — even at 99 years of age! He shot an older rifle in a beat-up stock, but he was there on the line with the rest of us. During one match Mike was having some problems and it was close to cease fire time. Our range officer could see that everyone else had finished. Mike kept shooting, trying to get five on paper. The range was quiet except for the reports from Mike’s rifle. When it was clear that all five were on paper, ‘cease fire’ was finally called. There were no questions as to what happened — all of us on the line realized it was a tribute to probably the only real Living Legend that any of us would meet, let alone shoot with….”

Mike Walker will be missed. As James Mock has written: “We in the shooting community are truly diminished. Mike was an icon of the innovative spirit of America.” Mike Walker was a true pioneer who has left an enormous legacy to all those engaged in the “pursuit of accuracy”.

Rest in Peace, Mike Walker. Thank you for your contributions to our sport.

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