Accuracy of .223 in a 5.56 barrel?

Will I see a loss of accuracy if I'm shooting .223 in a 5.56 barrel? Im thinking of going with a 20" 5.56 heavy barrel from Stag because A) It wont break my bank B) It's threaded, and I cant find any other barrels that are threaded that WONT break my bank. I've done some research and I can't find much on it, maybe I'm not looking hard enough, but I figured you guys would know best.

To add to this, it's a 1:9 twist, so the heaviest bullet I'll be shooting is about 70gr. I do plan to begin loading for it at some point in the near future.

Thanks!

 

Yes.

You will see much better accuracy with .223 Match or Varmint ammo then you will see with any FMJ military 5.56 Ammo you can get anywhere.

It's the nature of the bullets.
They are just Way Better bullets as far as accuracy potential then anything loaded in military grade FMJ 5.56 NATO.

rc

 

@Reloadron, yes, that's the barrel I'm looking at.

 

I am far from an expert as to the loads and brass casings but .223 bullets multiplied by 25.4 to convert to metric equals 5.6642. That is about as close to .223 as you can get without exceeding three decimal places. I think you are overthinking the possiblilities.

 

All things equal, same bore, different chambers. 5.56 chamber will shoot both. If anything the .223 Wylde chamber might squeeze a bit more accuracy. After the gets into the rifling, it doesn't matter what the chamber is. I prefer a .223 wylde or 5.56 NATO chamber over .223 regardless of other barrel specs.

I would worry more about buying a barrel from a quality manufacturer.

But, but, but.....we reload .224 bullets. lol.

 

5.56 NATO chambered Colt carbine firing .223 handloads.

Military FMJ bullet group on left side of target.
Varmint bullet group in center of target.



rc

 

Wow! That's pretty much night and day.

 

You never know how a barrel will shoot any brand of ammo until you actually shoot it

 

You'll find that ammo selection will make more of a difference than anything else when printing small groups. A nice, tight .223 match chamber is great, but it's not worth it in an AR platform. IMO a decent AR with handloads is plenty accurate.

 

223 VS 5.56 refers to the chamber dimensions not the bore diameter. 5.56 has a longer lead (and other minor dimension differences) which allows higher pressure ammo to be fired.

1/9 barrels are "iffy" for good accuracy with bullets heavier than about 60gr. Heavier bullets can work well but it will generally depend on the particular barrel and the length of the bullet (not the weight).

I consider 68gr match bullets by a few manufactures which are designed to work in 1/9 about the upper limit. A "match" chamber will be more demanding of ammo quality than a NATO chamber.

If you personally can hold better than .5 MOA (your ability, not the accuracy of the gun/ammo) consistently at 100yds then you might be able to tell the difference between chambers. Otherwise, I would choose the greater reliability and ammo choices of a NATO chamber.

 

Thought the chamber difference was so tracers could be shot with 5.56

 

SAAMI specs for the 223 Remington calls for a shorter leade than do the NATO specs for the 5.56. If your 223 rifle has a longer leade, then it's not cut to SAAMI specs. Not that it's a bad thing, it lets the reloader get a bit more velocity without going over the pressure limit.

5.56 is not loaded to higher pressures than the 223. It's loaded to make safe pressure in the 5.56 chamber. 223 ammo is loaded to make full pressure in a SAAMI spec chamber but it's pressure is reduced when fired in the 5.56 chamber due to the longer leade

 

"it's pressure is reduced when fired in the 5.56 chamber due to the longer leade"


<sigh>... So slightly as to be lost in the signal to noise ratio within the round-to-round variability of any production lot of ammunition. The bottom line is that you can barely even measure it with a crush gun.

Worry about the bullet stabilizing in your twist, and not what the headstamp on the cartridge is.



Willie

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It is a measurable difference. The "noise" is the result of not identifying the variables and controlling them. One variable is the differences in how SAAMI and NATO measure pressure. Another is that the pressure specified is maximum in chamber of minimum dimensions. The fact that it's a maximum measured in a minimum dimension chamber alone tells us the differences are significant.

When measured using the same methodology, 223 spec ammo does make less pressure in a 5.56 chamber than it does in a chamber held to 223 SAAMI specifications. See Lucky Gunner's article on the subject- http://www.luckygunner.com/labs/5-56-vs-223/#bookmark0

One source of noise is that commercial 223 chambers are not always held to SAAMI specs. The 700 with it's extra long leade mentioned by Reloadron is a perfect example. Another source of noise is when we forget is that we can increase velocity without increasing pressure by increasing case volume. One way to effectively increase case volume is to lengthen the leade. This allows the bullet to travel further (increasing internal volume) before engaging the rifling (which is where the bullet is when pressure peaks).

While what affect chamber and leade dimensions can get lost in the noise of variables, it's affect certainly can be measured and it can be significant. Otherwise, a load making high velocities with safe pressures in one rifle would be safe in them all. We know that's not true

 

^ Read the article critically, and there's no significant result shown other than that's there's no significant difference seen.


"When measured using the same methodology, 223 spec ammo does make less pressure in a 5.56 chamber than it does in a chamber held to 223 SAAMI specifications".

The difference is so insignificant as to not be of practical consequence, and for any one particular rifle the difference in ammunition selection may or may not result in increased or decreased accuracy.

The bottom line is that the differences are so slight as to not generally be measurable by a chronograph, and only marginally observable using strain guage equipment or a crush gun.


Let me leave the technical segue and answer the OP's actual question:


"Will I see a loss of accuracy if I'm shooting .223 in a 5.56 barrel?"

No, because the CASE dimensions, which is the variable you are asking about, are the same between the two cartridges.

With that said:

The bullet weight and the load itself will affect the result, but not the headstamp on the brass fed into the rifle.


Your rifle will tell you what it likes, all you need to do is to see what results you get with a variety of loads and stick to what works.


Willie

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The claim was made that NATO ammo is loaded to higher pressures than SAAMI ammo. This is not correct. It was claimed that the extra leade of the 5.56 does not reduce the pressure of 223 ammo fired in it. This is also not correct.

While the cases have the same dimensions, the chambers do not. Again, chamber dimensions affect pressure. Longer leades reduce pressure by increasing effective case volume. It's a trick Roy Weatherby used to stuff more powder in a case for better velocity while keeping pressures within acceptable limits.

While these factors may or may not have an affect on accuracy, passing off myths as fact clouds the issue

 

The TWIST rate was changed to 1:7 for military use for tracers, not the chamber.

 

Thank you guys so much for helping me out so far. It is greatly appreciated!

I have no intention of shooting military ammunition. So, Willie and MistWolf, if I am understanding this correctly, it means that the 5.56 chamber could tolerate hotter loads than a .223 chamber?

 

No, it only means it can tolerate longer bullets, and dirt, and out of spec cases in combat.

The pressure limits of the cartridge cases, and rifles both are chambered in are exactly the same.

A 5.56 NATO does not make brass or rifles actions stronger or able to handle higher pressure in the slightest.

rc

 

Tanks for clearing that up for me rc.

 

Just because one load of cheap 5.56 ammo shot less accurately than one target load of 223 proves nothing. Buy cheap ammo in 223 or 5.56 and you'll get equally poor results. Buy or handload quality ammo in either and you'll get equally good results.

 

"It was claimed that the extra leade of the 5.56 does not reduce the pressure of 223 ammo fired in it"

From a *practical perspective* the pressure difference is insignificant.

This statement is based on being a regular guest at Picatinny Arsenal for many moons, and watching many instrumented test barrel firings. The 5.56 v/s .223 question was a home-project question for a few of the guys there.

The difference in pressure between an identical .223 cartridge fired in the smallest tolerance SAAMI spec chamber and fired in the longest tolerance NATO spec chamber is on the order of 500 CUP. That's noise in the signal.


Willie

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