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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February 24th, 2015

NSSF Urges Public to Oppose ATF Ban on 5.56 M855 Ammo

BATFE ATF logoThe Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) is seeking to ban commonly-used 5.56 M855 “green tip” ball ammunition as “armor piercing ammunition” and is seeking public comment on the proposal. The National Shooting Sports Foundation (NSSF) urges target shooters and gun owners to contact ATF to oppose this proposed ban.

For decades, under the “sporting purposes” doctrine, commonly-available “green tip” M855 and SS109 rifle ammunition has been exempt from federal law banning armor-piercing ammunition. There is no question that this 5.56 ball ammo has been widely used by law-abiding American citizens for sporting purposes.

Winchester-brand 5.56X45 62gr NATO M855 FMJ Ammunition
m855 Olin winchester ball SS109 Brownells accurateshooter.com

NSSF SS109 M855 .223 Rem 5.56x45mm ammo ammunition penetratorThe NSSF has an online form that makes it easy to voice your opinion on the proposed ban on 5.56 ball ammo. This form will direct your comments to Congress and/or the ATF. Click the button at right to navigate to the NSSF online form.

Commentary by Jim Shepherd, The Shooting Wire
Should the ATF reclassify surplus (and widely used) M855 and SS109 ammunition as armor-piercing, it would then be illegal for consumer consumption. This weekend, we received word that apparently many gun owners didn’t find this to be a compelling reason to record their objections with the federal government. With only a few days remaining in the ATF’s solicitation of comments, fewer than 6,000 shooters have registered their displeasure with the proposal.That, as one of my least-favorite instructors used to say, is simply unacceptable.”

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