Shooting .223 in a 5.56 rifle

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I only rarely use 5.56 in my Colt AR15A2. I use mostly cheapo .223 Russian steel-cased stuff. For me, its largely a question of economics.
 
CornCod said:
I only rarely use 5.56 in my Colt AR15A2. I use mostly cheapo .223 Russian steel-cased stuff. For me, its largely a question of economics.
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Without looking I am not sure if your rifle is chambered for
the 5.56 or the .223.

If your rifle is chambered for the 5.56 you are ok to fire the
.223. If not, you are exceeding the chamber pressure of your
rifle to fire the 5.56 ammo as the longer case length of the
5.56 causes the bullet to be pushed further into the case,
which increases the pressure in the chamber when fired. This
will cause undue metal stress that can cause serious harm
to the rifle at some point. I would suggest you check on the
specifications of the chamber of your barrel.

The attached image shows the difference between the .223,
and the 5.56 rounds. If your chamber is for the .223 the
longer case length of the 5.56 round causes the bullet to
be pushed into the case. Just as automatic pistols chamber
the rounds on the basis of the case length, the chamber of
the rifle is made only long enough for the ammo it is
designed for so that the bullet is properly at the bore with
the rifling. You can see in the image that this rifle is with
the chamber for the 5.56, and that the bullet of a .223
would not quite be fully into the bore of the rifle.


Dave.
 

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i shoot .223 outta my M&P15 OR 5.56. :)

With iron sights I can hit steel at 450yds. :what:

Seems pretty accurate to me.;)

btw, I rarely see 5.56 ammo around.

be safe
 
While the original post was 5 years ago I'll add one quick comment.

Cast your chamber if you have doubts. That will tell you what is safe and isn't. I don't believe a single mass produced .223 rifle today is being shipped with a true .223 chamber. Some specialty target rifles/barrels maybe, but I have yet to hear a case where a .223 marked chamber was throated to original .223 spec. With big long heavy bullets and fast twists being popular today, everyone is throating long. It gets you around pressure issues when using 5.56 brass/loads and it gets you around guys jamming the ultra long loads way into the rifling. If you can't load to the rifling while fitting in a magazine, I don't see how a 5.56 or a .223 marked chamber matters nor where shooting either in that chamber would be an issue.

The issue with pressure is a bit overstated. What I find funny is that people claim a 5.56 is loaded hotter than .223 and a .223 barrel can't handle the extra press. Maybe, but both are coming from blanks of the same quality steel of the same size and weight. It isn't like we have .223 barrels that are safe at 55,000psi but can't handle being run at the 60,000psi that a 5.56 makes (assuming those earlier numbers are accurate). The problem is if a 60,000psi load is jammed to the lands raising pressure from there. So the simple answer is long throat the gun, which everyone I have seen is doing just that.

Pressure is a complicated game and it's very difficult to address all variables in a quick post. Many of the considerations are over my head. That said, a quick casting of the chamber or using an OAL gauge will tell you if your potential loads will be in the rifling (and potentially dangerous) or not. I know the chambers on all of my .223 or 5.56 marked barrels are throated far enough out that any commercially available 5.56 ammo I've found isn't a problem and doesn't show signs of dangerous pressure. I can't comment for your rifles nor advise you to use the wrong round/pressure range for the capability of your individual rifle. Figure out what you have and run ammo that is safe.
 
5.56 pressure is measured with a transducer at the case mouth...very late in the firing event...actual peak pressure is very likely near the limits of the strength of the brass (70,000 psi)...5.56 is essentially, a 223 loaded to magnum pressure...combine that with a jammed bullet in a short (SAAMI) chamber, and it's not unreasonable to expect pressures that may well "spontaneously disassemble" even a modern bolt action.

Think about it...5.56 is rated at 60,000 psi, but that pressure is measured after the bullet has moved...sort of the same principle as the Weatherby chambers....anybody wanna try firing a Weatherby round loaded to the hilt in a short chamber?
 
Angleiron said:
I bought my 5.56 because of the versatility of being able to shoot both types of rounds in a pinch, and was wondering if anyone else is shooting .223 in their 5.56 rifle? I know that it is not as accurate as a shooting these rounds out of a designated .223 rifle, but how much of a difference is there? I have the opportunnity to get 1000 rounds of .223 for a real good price, but if it is a big difference then maybe it is not worth it.
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You don't mention what your rifle is or more specific what the twist rate is?
You also don't mention the bullet weights of these 1,000 rounds of 223 or the bullet design?

So while once again we can beat the 5.56/223 debate to death I really see no way to answer your question beyond saying yeah, you can shoot 223 all day long and all night long in a rifle having a chamber cut for 5.56 NATO.

Ron
 
Where does the extra pressure come from?

Federal's 62gr .223 Remington load pushes that bullet 3020fps. It's marked .223 Remington. Lake City's 62gr 5.56 NATO 62gr XM855 load is published as 3020fps. It is marked 5.56 NATO. Would we consider Lake City 5.56 marked ammo to be a true 5.56 load or is it loaded light? There is minimal velocity difference between factory .223 ammo and factory 5.56 ammo, certainly hard to believe a 15,000psi difference is present from nearly identical cases shooting to nearly identical velocities. There is more to pressure than velocity, but in two similar cases firing the same bullet, it makes it hard to see why the NATO spec would call for a significant rise in pressure without also benefiting from a significant rise in muzzle velocity.
 
Books on the ballistics of ammo do not cover the
problem with pressure when shooting a 5.56 in a
barrel chambered specifically for the .223.

What happens when shooting a 5.56 in a .223
barrel, the throat is not long enough to properly
accommodate the extra length of the 5.56 from
that of the .223. The bullet of that 5.56 round is
jammed farther into the case. Since this reduces
the amount of space for the powder in the case
the pressure is also increased when fired.

The 5.56 Nato round was developed with a higher
pressure at detonation. This pressure, being more
than that of the current .223 round gets much less
space in the case, which increases the pressure
above that of the .223. with ignition of the powder.
Depending upon how far the bullet was pushed
into the case, the resulting pressure can exceed
the technical design of the .223 barrel.

There is no way of knowing how often this can
be done before the barrel literally explodes. Just
insure that you have a 5:56 barrel when shooting
the 5.56 ammo.

Dave.
 
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I've yet to see a barrel of a 223 "literally explode".
Considering most 223 chambers are of a more robust bolt style it's difficult to imagine they can't withstand the pressures of an auto.
Been pages wasted on this discussion.
 
benzy2 said:
Where does the extra pressure come from?

Federal's 62gr .223 Remington load pushes that bullet 3020fps. It's marked .223 Remington. Lake City's 62gr 5.56 NATO 62gr XM855 load is published as 3020fps. It is marked 5.56 NATO. Would we consider Lake City 5.56 marked ammo to be a true 5.56 load or is it loaded light? There is minimal velocity difference between factory .223 ammo and factory 5.56 ammo, certainly hard to believe a 15,000psi difference is present from nearly identical cases shooting to nearly identical velocities. There is more to pressure than velocity, but in two similar cases firing the same bullet, it makes it hard to see why the NATO spec would call for a significant rise in pressure without also benefiting from a significant rise in muzzle velocity.
Click to expand...
M855 will hit nearly 3,000 fps from a 16 barrel...

The Federal load you mention was most likely chrono'd from a 24" barrel...

Also, Uncle Sam places his chrono at 75 feet (IIRC)....Federal probably placed theirs at the traditional 10-12 feet.
 
And this is the sole result of Nato ammo in a 223 chamber?
There are many photos a destroyed firearms on the net, I guess, given the amount of violation I have committed regarding this issue I would be skeptical if it were to have happened to me personally.
Your example and the catastrophic results would indicate a much greater cause than that of the difference it the factory loads being discussed IMHO.
 
I'll ask this again, has anyone seen a non-custom chambered .223 marked barrel made in the last 2 decades that actually was tighter than a 5.56 spec at the throat? Has anyone cast a mold of their chambers to know how their rifles were actually cut? I haven't cast them all, but what I have seen is they all come back longer than minimum SAAMI spec. Only you can find out how your chamber was cut. If yours is cut to the minimum spec and you run 5.56 ammo in it, you may have a problem. If it's cut like the rifles I've seen, it won't make a bit of difference. Check for yourself or shoot what you like. I have confidence that nothing I own would have a problem either way.
 
All of the above considered, what happens when you then reload that .223 or NATO round and stick it in the chamber? This is a reloading section so how do you guys address reloading each type of that brass?

I address this the same way with 308 Winchester and 7.62X51 NATO. Once reloaded (and there are no 7.62X51 dies) it is simply a matter of SAMMI specifications or match for your barrel.
 
Makes me glad my rifle is clearly marked 5.56!
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The marking isn't what you should be interested in. My R51 is "marked" 9mm Luger, and yet a Luger finishing reamer only dropped halfway in when I went to clean up Big Rem's hack-job. Not saying whatever your gun is is a hack job, but it's what's inside that counts. Trust, but verify.

Personally, I think the whole "NATO Chamber" stuff is the exact same phenomena we've seen since forever in military guns; they have generous chambers so brass/gun fit is less of an issue. Makes things easier, cheaper, and more reliable all around (by which I mean, shooter, armorer, ammo sourcer, ammo manufacturer, and countless inspectors)

Unless you're see rifling grooves engraving or unfired cartridges having trouble chambering under their own weight, it's pretty much impossible for the variances described between the chambers to have much impact on anything. Yes, if innumerable factors line up to conspire against you, the civilian chamber spec could be the straw that breaks the camel. But so could be the fact your NATO Milspec Tacktical chamber was the last one cut before the reamer was thrown in the trash, and made it through with a narrow, rough, chattered, or uneven chamber.

Many guns, like the K31, were designed to have essentially zero freebore, with the rifling grooves contacting the ogive when chambered. No sign of those situations being particularly crazy, as far as pressure (though it obviously is a bit higher). The force required to start a bullet down a bore is like 100lbs; the bolt thrust on your rifles is like 60 times that. And in any case, bolt thrust is what actually matters, and less so what the bullet is doing.

It's worth remembering your AR barrel extension is an incredibly strong mechanical and geometric marvel that has a very healthy design safety margin. Stuff that bumps the design load 10% one way or the other (like a slightly higher pressure load or a hot day) will not have any bearing on practical safety. At worse, it may accelerate wear somewhat (oh noes, 18000 instead of 20000 cycles between mean failures :rolleyes:). Any gun so sensitive was never safe to fire in the first place (which some could argue certain low end parts may be. I'd be more worried they set my headspace wrong or forgot to heat-treat, than if they cut the wrong type of chamber in such a case, though)

TCB
 
HOOfan_1 said:
the dimensions of the brass are exactly the same.
Click to expand...

The 5.56 mm NATO and .223 Remington cartridges and chamberings are similar but not identical. While the cartridges are identical other than powder load, the chamber leade, i.e. the area where the rifling begins, is cut to a sharper angle on some .223 commercial chambers. Because of this, a cartridge loaded to generate 5.56mm pressures in a 5.56mm chamber may develop pressures that exceed SAAMI limits when fired from a short-leade .223 Remington chamber.
The result of this is that there is no such thing as "5.56 brass" or ".223 brass", the differences in the cartridges lie in pressure ratings and in chamber leade length, not in the shape or thickness of the brass.

Pressures are generated and measured using a chamber cut to 5.56 NATO specifications, including the longer leade. Firing 5.56mm NATO from a chamber with a shorter .223 Remington leade can generate pressures in excess of SAAMI maximums.

To always be sure your rifle is able to handle these extra pressures you must check your chamber. If your rifle barrel is marked as for 5.56mm NATO, you most likely have no problem on this issue. If it is stamped as for .223 ammunition, make a mold of your chamber and measure it to be sure.
 
the dimensions of the brass are exactly the same.
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The external dimension are, but the internal dimensions are not. True 5.56 brass is thicker, and every reloading manual will tell you to reduce .223 Rem loads when using military 5.56 brass to avoid exceeding max pressure.

External dimensions aside, the chamber dimensions differ significantly enough that firing full pressure 5.56 NATO loads in .223 REM chamber can be problematic.
 
This debate is theoretical and meaningless. Who is cutting a tight .223 Rem chamber and installing it today on a commercially available rifle? Not just mark the gun but who actually is running minimum throat spec and stamping it .223? You could call it 22lr for all I care. It's how the thing is cut that matters and nobody with lawyers on staff are letting 223 marked rifles go out the door with chambers that aren't safe with 5.56. They may suggest against it, but their lawyers aren't dumb and theydo get their way.
 
[QUOTE
Pressures are generated and measured using a chamber cut to 5.56 NATO specifications, including the longer leade. Firing 5.56mm NATO from a chamber with a shorter .223 Remington leade can generate pressures in excess of SAAMI maximums.
][/QUOTE]

Are these pressures really high enough to cause chamber failure? What pecentages are we talking about.

This issue is rehashed often and the same tribal knowledge is always repeated.
There is some CYA on the part of gun makers but not to the extent that they roll a warning on their barrels. I've never seen a warning on Nato spec ammunition like you find on ammo that fire in both black powder and smokeless guns.
To each their own, if you have Nato spec ammo and 223 rifle send me all you have, my guns don't seem to know the difference.



The external dimension are, but the internal dimensions are not. True 5.56 brass is thicker, and every reloading manual will tell you to reduce .223 Rem loads when using military 5.56 brass to avoid exceeding max pressure.

External dimensions aside, the chamber dimensions differ significantly enough that firing full pressure 5.56 NATO loads in .223 REM chamber can be problematic.
Click to expand...
 
First hand experience....

My 20 inch 556 BCM uppers periodically short stroke on some 223 ammo. Same ammo works fine 100% of the time in my Wylde chambered Rock River 20 inch uppers. I am not saying this is due to chamber dimensions, could be gas port size, but none-the-less the ammo makes a difference. All of the uppers work fine with 556 ammo.

My Mini 14 suffers frequent failures to fire / light firing pin hits with 556 ammo, presumably due to beefier primer cups.

Likewise my 308 M&P 10 works fine on 308 ammo and short strokes with some 7.62 ammo.
 
I have an AR that consistently failed to go into battery with all ammo I tried, a trip to the smith and his reamer fixed it to 100% reliability since. It is marked 556.
I suppose that there are many chambers that barely fall within spec due to their position in manufacturing and new or worn tooling. Some no doubt slip by as being out of spec.
 
When excessive pressures have happened they were not being measured
for the most part. Tests done after the fact have shown some pressures
to have attained over 71,000 pounds. Since the proper pressure for the
.223 is around the 49,000 pound range, and the 5.56 is around the
52,000 pound range, those pressures up around 71,000 pounds for a
5.56 fired in a .223 chamber can cause serious damage, and possible
injury.

This is not a game, nor an issue to bandy about. Heed the warnings
and just be sure of what you are using. If you wish to become a
ballistics expert, study it and do your own builds from scratch, and
test the weapons. You would need to become an engineer for the
math needed for your testings as well as knowing how to determine
the ballistics for and from any specs. Otherwise, just consider the
warnings as possible and use due caution.

Just remember that there is always a 50/50 chance that anything
can happen. That is not a degree of probability, just possibility.
 
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