223 vs 5.56 accuracy


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Old 05-29-2014, 03:10 PM   #1
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Default 223 vs 5.56 accuracy

I realize the 223 case is slightly smaller than the 5.56 case.
With the 5.56 chamber being larger, how does that affect accuracy when the 223 is fired in a 5.56 chamber.
It would seem that the looser 223 round would result in poorer accuracy.
Also, if a 223 round is fired in the 5.56, does that case now not fit a 223?



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Old 05-29-2014, 03:28 PM   #2
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Chamber is just very very very very very slightly longer in 556 than 223 but its so close that for all intents the same gages can be used on either. Even then it depends on who is setting the headspace in the first place. Leade is a little longer in 556 allowing use of longer ogived bullets.

You can get great accuracy with either chambering since the factors that determine accuracy aren't in the chamber itself. It has more to do with the type of rifling the condition of the throat how far the bullet is from the rifling the powder used the consistancy of the ammo the type of metal the barrel is made from and any coatings how smooth the rifling is cut.

Want a great sccurate barrel look more at who is making the barrel and how and what its made from along with the specs.

As for once fired cases. It doesn't matter. When its resized the dies are the exact same for 556 and 223. Its where you set the shoulder that matters. All semi auto brass should be full length sized. Fire forming brass on a semi easily causes feed issues. The brass is still under some pressure and hasn't fullly shrunk before it starts being extracted. This means the case can be slightly larger than if it sat there until manually extracted.

Typically 556 chambers aren't used on accuracy builds so your not going to find that on a barrel built for accuracy unless you special order such from a barrel maker.



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Old 05-29-2014, 03:29 PM   #3
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There is NO difference in the two rounds, just in the chamber of the firearm !..........

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Old 05-29-2014, 03:37 PM   #4
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the only rifle i have currently in 5.56/223 is my Bushmaster AR Carbine. i generally use the PMC 55 gr. FMJ rounds or the PMC X-Tac 62 gr. Green Tips. i really am not seeing a big difference in accuracy between the two rounds in my rifle.

the barrel on mine is marked 5.56 Nato, 1-9. the lower reciever is marked 223-5.56mm Nato.

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Old 05-29-2014, 04:33 PM   #5
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JonM nailed it.

Gun at left has a factory Colt 5.56 chrome lined barrel w/ 1:7 twist.
Gun at center has a Krieger .223Rem stainless steel barrel w/ 1:7.7 twist.

I shoot Lake City 5.56 military brass is both guns. However.... I do keep the brass segregated between the two guns, because I resize them to fit the individual chambers of the rifles.

Accuracy between the two is like night and day, just because of the quality and construction of the Krieger barrel - not because of it's caliber designation. Of course hand loading ammunition to properly fit any particular chamber goes a long way too, in getting the most accuracy possible from any gun ..... in my experience.

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Old 05-29-2014, 06:11 PM   #6
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so if you shoot the 5.56 ammo in the 223 why is it such a no-no by some sources. Does the 5.56 have higher pressures?
Why can't one just ream out a 223 barrel to fit the 5.56?

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Old 05-29-2014, 06:18 PM   #7
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Quote:
Originally Posted by montveil View Post
so if you shoot the 5.56 ammo in the 223 why is it such a no-no by some sources. Does the 5.56 have higher pressures?
Why can't one just ream out a 223 barrel to fit the 5.56?
apparently from some sources the 5.56 operates at a higher pressure than 223 ammo does. some sources say the cases are externally the same but that the interior dimensions are smaller on the 5.56 vs. the dimensions internally of the 223 cases.

please don't quote me on that. this debate has been ongoing for years now and i don't have a clearcut answer yet on this. but my thoughts are this, i use what is marked on the rifle as to what i would fire in a particular rifle.
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Old 05-29-2014, 06:20 PM   #8
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Quote:
Originally Posted by montveil View Post
so if you shoot the 5.56 ammo in the 223 why is it such a no-no by some sources. Does the 5.56 have higher pressures?
Why can't one just ream out a 223 barrel to fit the 5.56?
there is no need for that.. the bullets would still be the same diamieter(.224)
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Old 05-29-2014, 06:23 PM   #9
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Quote:
Originally Posted by montveil View Post
so if you shoot the 5.56 ammo in the 223 why is it such a no-no by some sources. Does the 5.56 have higher pressures?
Why can't one just ream out a 223 barrel to fit the 5.56?
Because of the leade in the throat. 556 has a bit longer space between the case mouth and the start of the rifling. This is to accomodate things like tracers ap and other special 556 ammo. The design of bullets for the 556 allows for a longer ogive. If you stick a pulled bullet from a military cartridge in a handloaded case and use 223 spec cases you still run a risk of kaboom.

You can use 556 in a 223 if you use a bullet comparater like the hornady one to find the max coal of a 223 rifle then measure the 556 cartridges at the ogive to be sure the round doesnt hit the rifling on chambering. To do this you need to send a once fired case out of that rifle to hornady to make a modified case for measuring. Cost is about 5$ not counting shipping. May be a bit more nowadays.

You can ream out to 556 spec but you have increase leade in the throat and thats not an easy thing to do without proper tools. For example the wylde chamber uses a 223 chamber with a 556 throat. The issue isnt really the chamber itself.
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Old 05-29-2014, 06:34 PM   #10
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Quote:
Originally Posted by Axxe55 View Post
, i use what is marked on the rifle as to what i would fire in a particular rifle.
This if your buying off the shelf.

If your a handloader just order the right case gages to start with and go from there. Have a bullet comparator and appropriate modified cases made from new once fired brass in that specific gun. Set your dies using the correct case gage test your coals on cartridge and rifle from the ogive stay within published book load data and you wont have issues


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