Why have both .223 and 5.56?

[JellyJar]

Given that the .223 Remington and the 5.56 NATO rounds are very similar why have both?

Is there an advantage of the .223 over the 5.56?

Thanks

JJ

 

[badkarmamib]

The chambers are different. .223 is tighter, giving better precision. 5.56 is looser, allowing for higher pressures. The debate continues to rage on whether the two rounds themselves are different, or simply measured differently...

 

[Robert101]

If you are a reloader it doesn't matter. We tend to size the ammo to the chamber. Keep in mind that there are no 5.56 dies. So guess what, It is only resizing the round to a longer case length that will govern. We do this all the time by fitting the case to a specific chamber regardless of the minor differences b/n 223 and 5.56.

One reason the 5.56 chambers are longer has been to account for more debris in the chamber area. Non military users don't have this concern.

 

[gotmine]

Now you're making me google and go measure.

 

[Malamute]

The chambers are different. .223 is tighter, giving better precision. 5.56 is looser, allowing for higher pressures.

I believe theres more to it than the "loose" chamber dimension. Looking at the specs of various reamermakers, theres some variation even within the same type, though the differences are small, with 5.56 having slightly more allowable headspace room. The primary difference regarding pressures is the throat or leade ahead of the chamber (the transition from the chamber mouth to the rifling). The 5.56 has more freebore than a commercial 223 chamber, which is one of the things Weatherby did to get the velocities they have from their chamberings. Many commercial guns have throats open enough to safely shoot 5.56, so just because example X of whatever model shoots tons of them and its marked 223 doesn't by any means mean any gun marked 223 is also safe to do so, its individual with the way the maker chose to ream the throat. Ruger has always stated that their 223 guns were safe to fire 5.56 ammo in.

Something rarely mentioned, a chamber, or a cartridge, isn't a PERFECT exact fit in a chamber. Theres allowable slop built into the data, its a range of size, not an exact number, for both chambers and ammo. The tolerances can stack up and create a loose fitting round in a particular chamber, and still be in spec. Ammo is often on the loose side of the specs so it fits in any gun, even ones on the small side of the specs. One rarely if ever sees factory ammo that's a true snug fit in a chamber. Something to keep in mind when discussing tiny differences in chambers. I believe the biggest practical difference between 223 and 5.56 is the throats. And as mentioned, those can vary from whatever the supposed exact spec is.

A good read on the subject, with chamber drawings and reamer specs of different makers and chamber types.

http://www.m4carbine.net/showthread.php?55149-5-56mm-NATO-versus-223-Remington-Chamber-Differences

 

[Bart B.]

Same reason the commercial .30-06 came out 110 years ago. Its origin was the US caliber 30 Model 1906 cartridge with a 150-gr bullet, in 1926 changed to Caliber 30 M1 with a 174-grain bullet, then in 1938 to Caliber 30 M2 with a 150-gr. bullet.

The .308 Winchester and 7.62x52 NATO round are in the same boat.

badkarmamib, how is the commercial .223 Remington chamber more "precise" than the military 5.56 NATO chamber; what's different in how the bullet's aligned with the bore when the round's fired if that's what "precise" implies? I've heard the same thing said about the .308 Win versus the 7.62 NATO, but top quality arsenal 7.62 barrels with their slightly different chambers didn't shoot good ammo any more accurate than custom barrels chambered for the .308 Win. in both M14 and M1 rifles with them.

 

[badkarmamib]

"When shooting .223 Rem. cartridges in a firearm chambered for 5.56x45 mm, it’s likely that there will be a degradation in accuracy and muzzle velocity due to the more generous chamber dimensions. That’s not to say that a firearm chambered in 5.56x45 mm won’t be accurate with .223 Rem. loads, only that, on average, the .223 Rem. chambered firearms will be more accurate with .223 Rem. ammunition than rifles chambered for 5.56x45 mm firing .223 Rem."

https://www.americanrifleman.org/articles/2013/3/4/223-remington-vs-556-whats-in-a-name/

This is a theory that benchrest shooters have been utilizing for years. I am not a benchrest shooter, I am just going by what I read; I tend to read a lot on the subjects pertaining to firearms, as it is something that interests me, even if I don't do as well at applying the data, or remembering the sources...

 

[Bart B.]

I understand the muzzle velocity differences.

Why is accuracy different? Both cartridges align the bullet with the bore the same way with the same precision when they're fired.

 

[badkarmamib]

I always assumed that it had to do with the increased throat area allowing greater possible variances in neck expansion, causing more "bullet wobble" before the bullet contacts the rifling. But, you know what happens when you assume...

Seriously, though, the .223 chambers are "supposed" to be designed closer to the dimensions of the ammo, compared to the looser chambers for 5.56 (to allow for crud build-up, among other things, as Robert101 mentioned). Precision is increased when clearances are minimized.

 

[Sunray]

Gives you an excuse...I mean, reason to have two rifles chambered in the same thing. Say a heavy barreled, bolt action, varmint rifle and one of the semi's.
"...there are no 5.56 dies..." No .223 Wylde dies either. The Wylde chamber is between the .223 and 5.56. Still loaded with .223 dies.
Neither is there such a thing as a SAAMI spec for 5.56NATO or the .223 Wylde. 5.56 is the NATO designation, period.

 

[Nature Boy]

Gives you an excuse...I mean, reason to have two rifles chambered in the same thing

I believe Sunray has the "A" answer. A bolt gun in .223 and an AR in 5.56

 

[Bart B.]

badkarmamib,

I don't think chambers that have less clearance to the cartridge align the cartridge neck any better to dead center in the chamber neck than those with more clearance.

Most benchresters recently changed over to full length sizing dies that made fired cases a bit smaller than neck only sized ones; such cases have more clearance to the chamber. Their smallest groups changed very little in size but their biggest ones shrunk quite a bit.

A 22 caliber bullet needing 23 pounds of force on it to push it out of the chamber neck (MIL SPEC for 5.56 NATO) and into the rifling needs only about 2400 psi to do that. The bullet will be into the rifling before it clears the case neck. And with that pressure, the neck won't expand hardly any amount at all. So the case neck will guide the bullet into the rifling before peak pressure expands the case totally against the chamber.

Don't forget, the case shoulder's driven hard into the chamber shoulder before the round fires; the firing pin drives it there before the primer fires. That's what centers the front of the cartridge in the chamber. It gets centered perfectly regardless of how much clearance there is around the cartridge case or case neck. The back end of the case may be pressed against the chamber wall by the extractor pushing it there, or anywhere else depending on how the case head moves from firing pin impact or how it locked up into battery when the firing pin hits the primer.

Nature Boy,

If two rifles are chambered for the same thing, they'll both be .223 Rem or 5.56 NATO. Some people chamber their AR's for the .223 cartridge.

 

[lysanderxiii]

New game: List the differences:

(NOTE: All dimensions are at theoretical intersection of lines.)





There is a similar game for .308 Winchester and 7.62mm NATO.

 

[Carl N. Brown]

The Jun 1994 Department of Justice Office of Professional Responsibility report on Ruby Ridge refers to the Weavers owning .223 Mini-14s and a .223 H&K, the marshals having ".223 caliber M16 rifles" and a ".223 caliber M16A2 Colt Carbine". Several matches in the PDF of the Jun 1994 report on .223 but none on 5.56.

I think drawing a line between .223 Remington and 5.56x45mm came when bullets heavier than 55 grains came into common use with the military loadings, requiring different bullet throats and rates of twist for barrels using 62gr bullets and heavier.

Similar German cartridges were used for hunting smaller deer, with bullets in the 70 grain range. With more Americans using .223/5.56 with heavy bullets for deer hunting, I suspect this distinction will disappear in new guns.

The older bolt action .223 rifles chambered, throated and rifled for varmint bullets in the 36 to 55 grain range do need precautions. Those older rifles are probably stressed by shooting 62 grain or heavier bullets and the rate of twist of their rifling may not stablize the longer heavier bullets.

Checking the Wikipedia pages referencing C.I.P. data:
"The 5.56×45mm NATO has 1.85 ml (28.5 grains H2O) cartridge case capacity."
"The .223 Remington has 28.8 grains (1.87 ml H2O) cartridge case capacity.

External dimensions are the same. This implies to me the average NATO 5.56x45mm case has slightly thicker case walls than the average commercial .223 Remington case.

 

[sirgilligan]

I have the CZ 527 Varmint with 1:9 twist barrel. The chamber is 5.56 NATO chamber.

This is the results of shooting .223 REM loads in a 5.56 chambered rifle.

 

[lysanderxiii]

As the neck diameter being more "precise"...

The neck diameter for an M16 (aka 5.56mm) chamber is 0.2540" in diameter.

The neck diameter for a SAAMI .223 Remington chamber is . . . . 0.2540" in diameter.


The shoulder diameter for an M16 (aka 5.56mm) chamber is 0.3553" in diameter.

The shoulder diameter for a SAAMI .223 Remington chamber is . . . . 0.3553" in diameter.


The body taper for an M16 (aka 5.56mm) chamber is 0.01746" per inch.

The body taper for a SAAMI .223 Remington chamber is . . . . 0.0175" per inch.


The free bore diameter for an M16 (aka 5.56mm) chamber is 0.2265" in diameter.

The free bore diameter for a SAAMI .223 Remington chamber is . . . . 0.2240" in diameter.


The free bore length for an M16 (aka 5.56mm) chamber is 0.0569" in diameter.

The free bore length for a SAAMI .223 Remington chamber is . . . . 0.0250" in diameter.


The leade taper for an M16 (aka 5.56mm) chamber is 0.0427" per inch included angle.

The leade taper for a SAAMI .223 Remington chamber is . . . . 0.0555" per inch included angle.

The forth and fifth ones are where accuracy improves.

 

[lysanderxiii]

External dimensions are the same. This implies to me the average NATO 5.56x45mm case has slightly thicker case walls than the average commercial .223 Remington case.

Unless they are using a denser material, that doesn't bear out in the weights of the cases.

On average, they all weigh the same.

 

[denton]

Federal and Lake City brass have slightly greater capacity than most 223 Rem brass.

The upper pressure spec for 5.56 is higher than 223 Rem, and it is loaded hotter. The Accurate reload manual lists 5.56 loads at 62,350 PSI. The military pressure measurement system is different from SAAMI, which makes comparison of pressures a little sporting.

The COL spec for 5.56 is longer than the 223 Rem, but it doesn't matter. The maximum length the M16 magazine will allow only 223 Rem length ammo, so it gets loaded with shorter than maximum COL.

Military machine guns that shoot 5.56 compress the length of the case by an astonishing .014". If you reload Lake City brass that was fired in a machine gun, you may be asking for case head separation.

My bolt action is marked 223 Rem/5.56x45, so at least one manufacturer says their gun will accommodate both. Both my semi-autos are rated for both.

 

[mjsdwash]

ive notices that the crappy wolf type ammo has far better extraction in 223 chambers than 5.56, and always attributed that to the slightly wider dimension of the NATO chamber(since bad extraction has now been proven to be from poor obturation, and carbon gluing) where its easier for low pressure to expand. Does not address the OP, but some thoughts on where the topic has moved to.

 

[Dr T]

For me, it boils down to two factors.

If the rifle you want (need, lust for) is available in 223 but not 5.56, you really NEED a 223.

If you want to shoot a bunch of milsurp ammo, you need a 5.56.

The ballistics are not a factor for me given the similarity of the cartridges.

 

[jmr40]

For most practical purposes they are interchangeable. The military calls it 5.56 and the civilian load is 223.

Yes there CAN be differences in the max pressure and minor differences in chamber and case specs. But the differences are very slight you'll see just as much differences between manufacturing tolerances when comparing rifles or ammo from different manufacturers in any cartridge. You'll see far greater differences between various commercial 30-06 loads and rifles. Yet we only have 1 name for 30-06 while there are at least 3 distinct loading levels. Some rifles have tight chambers, others very loose, but they are all stamped 30-06.

In extremely rare cases you could end up with a 5.56 case that is on the large end of the specs that will have problems in a 223 chamber cut to minimum specs. But owners of 30-06 rifles have had the same problem for over 100 years.

I've yet to hear of a documented case of a 223 rifle having anything break from firing 5.56 ammo. But I've known of several problems with 30-06 stamped ammo causing problems in 30-06 stamped rifles.

 

[Casefull]

Federal and Lake City brass have slightly greater capacity than most 223 Rem brass.

I am not sure that makes sense as the thicker walls of the lake city brass actually decreases the available volume of the case. I have not checked 223/556 but I specifically reload my hunting 308/7.62 rounds using winchester brass because the case holds 2 to 3 g more powder than lake city and other heavy military brass.

 

[lysanderxiii]

Federal and Lake City brass have slightly greater capacity than most 223 Rem brass.

The upper pressure spec for 5.56 is higher than 223 Rem, and it is loaded hotter. The Accurate reload manual lists 5.56 loads at 62,350 PSI. The military pressure measurement system is different from SAAMI, which makes comparison of pressures a little sporting.

The COL spec for 5.56 is longer than the 223 Rem, but it doesn't matter. The maximum length the M16 magazine will allow only 223 Rem length ammo, so it gets loaded with shorter than maximum COL.

Military machine guns that shoot 5.56 compress the length of the case by an astonishing .014". If you reload Lake City brass that was fired in a machine gun, you may be asking for case head separation.

My bolt action is marked 223 Rem/5.56x45, so at least one manufacturer says their gun will accommodate both. Both my semi-autos are rated for both.

The maximum COL for M855 and M193 is 2.26", per the drawing.

The SAAMI maximum COL is 2.260".

The same.

The difference is SAAMI allows shorter COLs to accommodate lighter or different profile bullets. The military, only using a few bullet types and all having similar nose profiles, and lengths, needs to keep the COL held to tighter tolerances to maintain case volume.

As to the pressures...

The maximum allowable average pressure for M193 is 55,000 psi. The maximum allowable average pressure for M855 up until 1999 was 55,000 psi, after 1999 the pressure was bumped up 3700 psi, to 58,700. The STANAG 4172 maximum allowable average pressure for NATO standard ammunition is still listed as 55,000 psi. These are the pressure measured by pressure transducer at the case mouth from a STANAG standard test barrel, conformal or a perforated mid-case pressure transducer measurement is allowed but are calibrated against the case mouth standard.

The SAAMI maximum suggested allowable pressure for .223 Remington is 55,000 psi from a SAAMI minimum chamber, but allows for averages to be as high as 58,500 psi. SAAMI recommended pressure levels are based on perforated mid-case transducer measurement. Although, I'll bet most people use conformal gauges, as it is simpler and quicker, and can give the same results if calibrated against the mid-case transducer standard.

Military ammunition can be hotter if fired in a .223 chamber, due to the throat differences. When fired in their respective chambers, the pressures are comparable.

 

[Steel Horse Rider]

The difference is so that people will have more useless things to argue over, therefore occupying more time and intraweb space....

 

[lysanderxiii]

I am not sure that makes sense as the thicker walls of the lake city brass actually decreases the available volume of the case. I have not checked 223/556 but I specifically reload my hunting 308/7.62 rounds using winchester brass because the case holds 2 to 3 g more powder than lake city and other heavy military brass.

It does if you abandon the notion that "all military brass is thicker..." It isn't necessarily true for 5.56/.223.

OH, and there is one other thing....

There are two different types of 5.56mm NATO cases, at least in the US inventory, and they are different in a number of respects but the major difference internally is the web thickness, the distance from the bottom of the primer pocket to the back of the inside surface is a minimum of .055" for one, and a minimum of .065" for the other.