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:
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:
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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Displayed are results with Federal Gold Medal Match — quite impressive accuracy!
Criterion Barrels has published an interesting Ammo Comparison Test, shooting seven (7) different varieties of .223 Rem ammunition out of an AR15 fitted with Criterion Barrel. Each ammo type was chronographed (10-shot string), then five-shot groups were shot at 100 yards. Along with handloads (69gr Sierra MK + Varget), six (6) types of commercial ammo were tested:
PREMIUM Type Ammo:
Federal Gold Medal Match (69gr SMK)
Creedmoor 75gr HPBT
Prime 77gr OTM (Open Tip Match)
BULK Type Ammo:
Federal American Eagle XM193 (55gr FMJ)
Wolf Gold (55gr FMJ)
Wolf Polyformance Steel Case (55gr FMJ)
Here are the results for the four best commercial ammo types tested: Federal Gold Medal Match (GMM) with 69gr SMK, Prime 77gr OTM, Creedmoor 75gr HPBT, and American Eagle XM193 (55gr FMJ). The Gold Medal Match shot the best of all factory ammo tested. In fact, the GMM even shot slightly better than the handloads, which averaged 0.79″ for the three accurized groups.
The results are quite interesting. The Federal GMM actually shot the best, beating “untailored” handloads. Basic accurizing efforts and a much better rest set-up showed significant benefits with most ammo types (but not the bulk Wolf Ammo). As you would expect, the more expensive ammo shot best: “Chart 1.2 [below] showcases the average [after accurizing] five-round group sizes with each type of ammunition at 100 yards, while Chart 1.3 lists the price per round of each ammunition type. It becomes immediately evident by reviewing these two graphs that there is an inverse relationship between group size and factory ammunition price.”
Accurizing Improvements — Better Scope, Better Rests, Accu-Wedge
As you would expect, some basic accurizing efforts improved accuracy with the better ammo. The accurizing process included: 1) Swapping to a Vortex Viper PST Gen 1 6-24x50mm optic; 2) Adding an Accu-Wedge; 3) Improving fitment during reassembly, and 4) Switching from Harris bipod to a Sinclair Front Rest and Edgewood rear bag for added stability. The same 1:8″-twist Criterion barrel was used throughout the testing process.
If you shoot an AR15, or even shoot a .223 Rem bolt gun with factory ammo, you should probably read this test in full. Criterion put a lot of time into the testing, and experimented with a variety of AR options showcased in a series of YouTube videos. SEE: Accurizing the AR-15 Video Playlist.
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We often receive questions from varmint hunters and AR shooters regarding barrel length. They want to know how much velocity they will loose if they run a shorter barrel in their .223-Rem rifle. Our friends at Rifleshooter.com did a test that provides some surprising answers to that question.
With barrels, one always wonders “Can a little more length provide a meaningful velocity gain?” To help answer that question, Rifleshooter.com performed an interesting test, cutting the barrel of a .223 Rem rifle from 26″ all the way down to 16.5″. The cuts were made in one-inch intervals with a rotary saw. At each cut length, velocity was measured with a Magnetospeed chronograph. To make the test even more interesting, four different types of .223 Rem/5.56 ammo were chron’d at each barrel length.
Test Barrel Lost 25.34 FPS Per Inch (.223 Rem Chambering)
How much velocity do you think was lost, on average, for each 1″ reduction in barrel length? The answer may surprise you. The average speed loss of the four types of .223/5.56 ammo, with a 9.5″ shortening of barrel length, was 240.75 fps total (from start to finish). That works out to an average loss of 25.34 fps per inch. (See inch-by-inch data HERE.)
5.56/.223 Barrel Cut-Down Speed Test 26″ to 16.5″
Start FPS at 26″
End FPS at 16.5″
Total Loss
Average Loss Per Inch
UMC .223 55gr
3182*
2968
214
22.5 FPS
Federal M193 55gr
3431
3187
244
25.7 FPS
Win m855 62gr
3280
2992
288
30.3 FPS
Blk Hills .223 68gr
2849
2632
217
22.8 FPS
*There may have been an error. The 25″ velocity was higher at 3221 fps.
Rifleshooter.com observed: “Cutting the barrel from 26″ to 16.5″ resulted in a velocity reduction of 214 ft/sec with the UMC 223 55-grain cartridge, 244 ft/sec with the Federal M-193 cartridge, 288 ft/sec with the Winchester M855 cartridge and 217 ft/sec with the Back Hills 223 68-grain match cartridge.”
How the Test Was Done
The testers described their procedure as follows: “Ballistic data was gathered using a Magnetospeed barrel-mounted ballistic chronograph. At each barrel length, the rifle was fired from a front rest with rear bags, with five rounds of each type of ammunition. Average velocity and standard deviation were logged for each round. Once data was gathered for each cartridge at a given barrel length, the rifle was cleared and the bolt was removed. The barrel was cut off using a cold saw. The test protocol was repeated for the next length. Temperature was 45.7° F.”
Much Different Results with 6mmBR and a Longer Barrel
The results from Rifleshooter.com’s .223/5.56 test are quite different than the results we recorded some years ago with a barrel chambered for the 6mmBR cartridge. When we cut our 6mmBR barrel down from 33″ to 28″ we only lost about 8 FPS per inch. Obviously this is a different cartridge type, but also our 6mmBR barrel end length was longer than Rifleshooter.com’s .223 Rem start length. Velocity loss may be more extreme with shorter barrel lengths.
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Need .223 Rem ammo for your early summer varmint safari? Grafs.com has you covered. Over the past few months, Graf & Sons has acquired a large supply of .223 Rem ammo from a variety of manufacturers. Now Grafs.com has a great selection of .223 Rem ammo, with many items marked down on sale. You’ll find name-brand ammo for as little as $9.99 per 20-ct box (American Eagle 50gr JHP). If you prefer heavier bullets for longer-range shooting, check out the PRVI Partizan ammo loaded with 75gr HPBT match bullets — this is just $10.99 per per 20-ct box.
Olin’s Winchester Division has issued a Recall Notice for one (1) lot of its 5.56x45mm M855 62 grain PENE centerfire rifle ammunition. This notice applies only to Symbol Number ZGQ3308 with Lot Number WCC10M106-004. Other Symbol Numbers or Lot Numbers are not subject to this recall.
Symbol Number: ZGQ3308
Lot Number: WCC10M106-004
Winchester states: “Through extensive evaluation Winchester has determined the above lot of 5.56mm M855 ammunition may contain incorrect propellant. Incorrect propellant in this ammunition may cause firearm damage, rendering the firearm inoperable, and subject the shooter or bystanders to a risk of serious personal injury when fired.”
The ammunition Symbol Number and Lot Number are ink stamped on the outside of the 900-round shipping container, and on the outside of the 30-round carton as shown at right:
If you have Winchester Ammo with Symbol Number ZGQ3308 and Lot Number WCC10M106-004 immediately discontinue use and contact Winchester toll-free at 866-423-5224 for free UPS pick-up of the recalled ammunition. Upon receipt of your recalled ammunition, Winchester will ship replacement ammunition directly to you.
If you have any questions concerning this 5.56mm M855 ammunition recall please call toll-free 866-423-5224, write to Winchester (600 Powder Mill Road, East Alton, IL 62024 Attn: 5.56mm M855 Recall), or visit www.winchester.com.
Notice tip by EdLongrange. We welcome reader submissions.
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LuckyGunner.com, a leading online ammo vendor, has conducted a remarkable “torture-test” comparison of brass-cased and steel-cased .223 Rem ammunition. Four different kinds of ammo (one brass-cased, three steel-cased) were fired through four different Bushmaster AR15s — ten thousand (10,000) rounds PER GUN. The idea was to see if brass-cased ammo was better than the cheaper, steel-cased ammunition. During the course of the project, Luckygunner’s testers logged malfunctions and checked for accuracy, chamber pressure, gas port pressure, chamber wear, and overall barrel wear. At the end of the test, the well-worn barrels were sectioned to see the effect of thousands of rounds… and the results weren’t pretty.
Test Findings: For a multitude of reasons, the test crew determined that Federal brass-cased ammo was “healthier” than steel-cased ammo. The brass-cased ammo shot more accurately, had far fewer malufunctions, and produced less barrel wear. The USA-made brass-cased ammo also showed more consistent velocities. CLICK HERE to READ FULL TEST.
Watch the video below for a summary of results:
Torture Test Procedure
Four types of .223 Rem ammo were tested: Federal brass-cased 55gr FMJBT; Wolf steel-cased (polymer coating) 55gr FMJ; Tula steel-cased (polymer coating) 55gr Bi-Metal Jacket; Brown Bear steel-cased (lacquer coating) 55gr Bi-Metal Jacket. Each ammo type was paired with a specific Bushmaster AR-15. Tests were performed at various round-count stages:
At the start: record accuracy, velocity, chamber and gas port pressures, make chamber cast
After 2,000 rounds: record accuracy, velocity
After 4,000 rounds: record accuracy, velocity
After 5,000 rounds: record throat erosion, make chamber cast
After 6,000 rounds: record accuracy, velocity
After 8,000 rounds: record accuracy, velocity
After 10,000 rounds: record accuracy, velocity, chamber and gas port pressures, throat erosion, extractor wear, chamber cast, barrel wear, make chamber cast.
During testing, rifles were cleaned according to a preset schedule and temperatures were monitored. After testing, LuckyGunner sectioned the barrels and made careful inspections.
Click the links below for specific data, test results, and conclusions:
During the testing process, all malfunctions of each rifle-ammo combination were logged. The brass-cased Federal ammo was the clear winner:
Federal: 10,000 rounds, 0 malfunctions. Brown Bear: 10,000 rounds, 9 malfunctions
(5 stuck cases, 1 mag-related failure to feed, 3 failures to cycle.) Wolf: 10,000 rounds, 15 malfunctions (stuck cases) Tula: DNF (6,000 rounds in alternate carbine, 3 malfunctions)
Barrel Wear and Throat Erosion
Some of the barrels didn’t make it to 10,000 rounds: “The steel cased/bimetal jacketed ammunition caused accelerated wear to the inside of their respective bores. While the barrel of the Federal carbine had plenty of life left, even after 10,000 rounds … the Wolf and Brown Bear barrels … were completely shot out by 6,000 rounds. At the end of the test, the chrome lining of the Wolf and Brown Bear barrels was almost gone from the throat forward, and the barrels had effectively become smoothbores[.] A throat erosion gauge could be dropped into the bore from the muzzle end with absolutely no resistance.”
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Wilson Combat has come up with a new cartridge, dubbed the 7.62×40 WT (Wilson Tactical). Basically it is a .223 Remington necked up to .308 caliber, i.e. a .30-.223 Rem Wildcat. The cartridge is designed to give .30-cal capability to a standard AR15, using the normal bolt assembly and standard AR15 magazines. An AR15 can be converted to shoot the 7.62×40 WT with just a barrel swap. Note: Don’t confuse this new cartridge with the 7.62×39, the Eastern Bloc military cartridge that has been around for decades. The 7.62×40 WT is not derived from the 7.62×39 in any way. The 7.62×39 has a larger rim size, more body taper, and requires a different magazine and bolt. There have been 7.62×39 adaptations for ARs, but most didn’t function well (usually because of magazine issues). Wilson Combat claims the 7.62×40 WT offers the hitting power of the 7.62×39, but with a cartridge design that feeds and functions 100% in an AR15.
The 7.62×40 WT was designed around an optimal overall cartridge length of 2.250” which is a perfect fit for standard AR mags without shoving the bullet too far down in the case. Wilson says that its 7.62×40 WT barrels are optimally throated for the 2.250″ COAL. Therefore, Wilson claims, the “7.62×40 WT does not suffer from the same inconsistent accuracy issues in the AR platform often seen with the 300 Whisper and 300 BLACKOUT.”
Here are comparative Velocity and Energy numbers for the 7.62×40 WT vs. other cartridges with which it will compete.
7.62×40 WT (16″ Barrel)
110 gr: 2450 FPS Muzzle Velocity and 1466 Foot Pounds of Energy
125 gr: 2400 FPS Muzzle Velocity and 1599 Foot Pounds of Energy
150 gr: 2200 FPS Muzzle Velocity and 1612 Foot Pounds of Energy
5.56 NATO (.223 Rem) (16″ Barrel)
55 gr: 3150 FPS Muzzle Velocity and 1212 Foot Pounds of Energy
62 gr: 3000 FPS Muzzle Velocity and 1239 Foot Pounds of Energy
77 gr: 2750 FPS Muzzle Velocity and 1293 Foot Pounds of Energy
7.62×39 (16″ Barrel)
123 gr: 2320 FPS Muzzle Velocity and 1470 Foot Pounds of Energy
6.8 SPC (16″ Barrel)
110 gr: 2550 FPS Muzzle Velocity and 1594 Foot Pounds of Energy
At first it looks like the 7.62×40 WT has more energy than a 7.62×39 and outruns a 6.8 SPC handily. But Wilson omitted some key data for the 7.62×39. Taking load info straight from the Hodgdon Reloading Center, a 7.62×39 can be loaded to 2408 fps with a 125gr bullet, or to 2192 fps with a 150gr bullet at relatively moderate pressures (under 41,000 CUP, or roughly 44,250 psi). A 7.62×39 launching 150-grainers at 2192 fps generates 1601 foot-pounds, virtually the same as Wilson’s 150gr load. So, the 7.62×40 WT has no real advantage (over the 7.62×39).
Is This Cartridge Needed at All?
The “T” in 7.62×40 WT stands for “Tactical”, but we don’t think many police or military units will adopt this round. The 5.56x45mm is too well-established in the AR15/M16 platform and the 7.62×39 is the smart .30-Cal choice for an AK. So what, then, is the real “niche” for the 7.62×40 WT?
We think this round may prove popular with hunters who want to shoot a much heavier bullet out of a standard AR. A 150gr projectile is nearly twice as heavy as the biggest projectile you can shoot from a .223 Rem AR. The bigger bullet should work better on some kinds of game. Wilson Combat says: “Designed for tactical/defense applications as well as hunting for medium-sized game such as deer and feral hogs. For hunting the 7.62×40 WT vastly out performs the 5.56 and is on par with the 6.8 SPC at ranges out to 175-200 yards. The VERY mild recoil of the 7.62×40 WT also makes it ideal for female and younger shooters as well as anyone that’s recoil sensitive.”
Wilson says the 7.62×40 has proven itself as a good hunting cartridge: “A LOT of Texas feral hogs, whitetail deer and predators lost their lives testing the terminal performance of this cartridge! The 7.62×40 WT has proven to be a VERY efficient killer on medium sized game with the 110gr Barnes TTSX, 125gr Nosler Ballistic Hunter and the 125gr Sierra Pro Hunter. Any of these three bullets perform admirably on deer and hogs under 150 lbs. or so, but we recommend the 110gr Barnes TTSX for large hogs. The 110gr Sierra HP is a great bullet in the 7.62×40 WT for varmints and predators, and has proven to be one of the most accurate bullets.”
For home defense, it could be argued that the 7.62×40 WT is better than the .223 Rem because the larger, slower .30-Cal projectile has less penetration (through walls), but that would have to be demonstrated with real-world testing. Moreover, there are frangible .224-cal bullets that minimize the risk of over-penetration indoors.
Some benchresters might even tinker with the 7.62×40 WT in a bolt gun for score competition, but we doubt it would prove competitive with the 30 BR which can push a 120gr bullet at around 3000 fps. Wilson’s cartridge does give a paper-puncher the ability to shoot a .30-caliber bullet from a rifle with a .223 bolt face, and that might be attractive to club shooters in informal score matches.
Wilson Combat will be selling 7.62×40 WT loaded ammunition (with 110gr or 125gr bullets), but it is also supporting the reloading market. Wilson offers 7.62×40 WT brass, Hornady 7.62×40 WT dies, and you’ll find extensive load data on the Wilson Combat website. For those who want to put together a 7.62×40 WT AR, Wilson offers pre-chambered 7.62×40 WT barrels, as well as complete 7.62×40 WT uppers. Barrels start at $249.95, while the 7.62×40 WT uppers retail for $1024.95.
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MidwayUSA now offers milspec 5.56x45mm Lake City brass (item 197849) at $114.99 per 500 cases. That works out to just $23.00 per hundred. Shooters report this brass is “very uniform” and shoots great in AR-type rifles. It can also be used in rifles chambered for the .223 Remington. MidwayUSA reports: “This is true 5.56x45mm mil-spec, new, unfired, heavy duty brass with the LC 09 headstamp. It is the same brass supplied to our fighting forces in Iraq and Afghanistan. We made a special buy on a limited supply and it will not last long. Cases should be sized, neck-chamfered, and deburred before loading. With this brass, there is no primer crimp to remove.”
User Report: “Brand new Lake City brass made to 5.56 NATO spec, fresh annealed necks and no primer crimp. It cycles perfectly fine in my AR, loads with no fuss, and I’ve had NO issues with it.” — J.H. from Abilene, TX
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Winchester states: “Through extensive evaluation Winchester has determined the above lot of 5.56mm M855 ammunition may contain incorrect propellant. Incorrect propellant in this ammunition may cause firearm damage, rendering the firearm inoperable, and subject the shooter or bystanders to a risk of serious personal injury when fired.”
Barrel Wear and Throat Erosion
At first it looks like the 7.62×40 WT has more energy than a 7.62×39 and outruns a 6.8 SPC handily. But Wilson omitted some key data for the 7.62×39. Taking load info straight from the 
For home defense, it could be argued that the 7.62×40 WT is better than the .223 Rem because the larger, slower .30-Cal projectile has less penetration (through walls), but that would have to be demonstrated with real-world testing. Moreover, there are frangible .224-cal bullets that minimize the risk of over-penetration indoors.
