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Old 01-28-2011, 16:18   #1
JKD99
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.223 rounds

I'm just now ordering my first AR and have a question about ammo. I know that .223 can be fired in a 5.56 but some say that it affects accuracy due to the longer leade space. Do any of you actually notice a difference in accuracy between the two different rounds?
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Old 01-28-2011, 16:30   #2
boomhower
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Unless you are using very high quality match ammunition your not going to notice much difference one way or the other. You typical ammo is going to be 2-3 MOA at best.
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Old 02-08-2011, 20:00   #3
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Anyone who reloads knows that the exterior case dimensions of cases marked 5.56 and cases marked .223 are absolutely identical to a thousandth of an inch. It's the same cartridge, 5.56 is just loaded to higher pressure. It's like comparing 9mm and 9mm +P. Brass thickness is all over the place with both headstamps, but 5.56 tends to be slightly thicker on average.
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Old 02-09-2011, 03:51   #4
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Originally Posted by JKD99 View Post
I'm just now ordering my first AR and have a question about ammo. I know that .223 can be fired in a 5.56 but some say that it affects accuracy due to the longer leade space. Do any of you actually notice a difference in accuracy between the two different rounds?
Not much and I don't know if the difference is due to .223 vs. NATO or due to .223 I shoot being crappy ammo in general. I see about 4 inches of difference between the POI of say Fiocchi .223 and Federal 5.56.

I do see a bigger difference in accuracy between 55gr and 62gr shot form 1/7 barrels.
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Old 02-09-2011, 04:09   #5
Dasglockenspiel
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I reload blem 55 FMJs & 55 Hornady BTs w/mixed brass (223 / 5.56) with medium power loads of Accurate 2150.

Stock Bushmaster 16" (base model, w/ polished trigger) produces close to 1 1/2" (3 shot) groups at 100 yds.

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Old 02-09-2011, 11:31   #6
Gunnut 45/454
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mboylan
Not true! Actually there 's a .010" difference between .223 Rem and 5.56mm! Every .223 Rem case I've shot then sized run 1.745"-1.755"! All 5.56mm rounds I've shot and resized run 1.760"- 1.770" The book trim to size for .223 Rem is 1.750" I trim too and size my cases to the 5.56mm lenght of 1.760" ! Shooting 5.56mm in a .223Rem chamber and your shoving .010 of the brass into the lead! Not good- you may get away with it but do you really want to chance an overpressure?
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Old 02-09-2011, 13:19   #7
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mboylan
Not true! Actually there 's a .010" difference between .223 Rem and 5.56mm! Every .223 Rem case I've shot then sized run 1.745"-1.755"! All 5.56mm rounds I've shot and resized run 1.760"- 1.770" The book trim to size for .223 Rem is 1.750" I trim too and size my cases to the 5.56mm lenght of 1.760" ! Shooting 5.56mm in a .223Rem chamber and your shoving .010 of the brass into the lead! Not good- you may get away with it but do you really want to chance an overpressure?
Wrong, the specs for unfired cases are exactly the same. Trim to length for cases marked 5.56 and. 223 is 1.750. If cases are at 1.760, they need to be trimmed. Higher pressures will cause higher brass flow and increase neck lengthening after firing. Cases loaded to 5.56 pressures will need more trimming and survive fewer reloads.

PS. Most of the once fired 5.56 marked brass I find is stretched out of spec as well. It behaves itself when loaded to .223 pressures.

Last edited by mboylan; 02-09-2011 at 18:10..
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Old 02-09-2011, 20:24   #8
Gunnut 45/454
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Wrong case length for 5.56mm!

http://www.ask.com/wiki/5.56x45mm_NATO

Case Length for .223 Rem Set by SAAMI is 1.750" Every load manual I've seen has this length! If they are the same then why all the warnings in the manuals saying not to shoot 5.56mm in .223 Rem chambers -Why no list of 5.56mm load data? Why do we see on occasional the blow up of .223 Rem chambered gun by 5.56mm ammo? The reason why is that if you stuff the case into the lead you dematically raise pressures this is because 5.56mm cases are .010" longer then factory .223 Rem! There are no cases that grow at .025-.030" when fired! Sorry that one don't fly! Most cases grow no more then .005"-.010" maybe ! I don't know how long you've been reloading but I've been doing it for darn near 30 years and I've never seen any case grow that much!! In fact I shot some 5.56mm rounds today that I reloaded with the trim length of 1.760" after resizing they grew a hole .001" or not at all with a max load!
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Old 02-09-2011, 20:39   #9
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Originally Posted by JKD99 View Post
I'm just now ordering my first AR and have a question about ammo. I know that .223 can be fired in a 5.56 but some say that it affects accuracy due to the longer leade space. Do any of you actually notice a difference in accuracy between the two different rounds?
Without getting technical on the pressure issue as you are asking about accuracy, yes, I find that .223 fired out of a 5.56 chamber is less accurate than if you fire that same .223 out of a .223 chamber.

Accuracy is mostly comprised of how consistently a bullet chambers exactly the same each and every time. With the longer leade in the 5.56 chamber and more freebore space, this can cause a very small inconsistency in how the bullet chambers each and every time. For precision shooting with say an optic, you can often get noticeable results between the 2 rounds. Now if you are going for combat accuracy of say 10" groups in a rapid fire and up close scenario, you aren't going to notice a thing.
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Old 02-09-2011, 22:51   #10
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5.56 load data is definitely out there.

.223 Pressure

TAC 62 MIL M855 22.5 2,800 25.0 3,078 54,947 2.260
TAC 62 MIL FMJ 22.3 2,825 24.8 3,084 54,787 2.223
TAC 62 BAR TSX 22.5 2,804 25.0 3,066 54,333 2.255

5.56 Pressure

TAC 62 MIL M855 23.6 2,940 26.2 3,219 62,350 2.260
TAC 62 MIL FMJ 23.3 2,935 25.9 3,217 61,977 2.223
TAC 62 BAR TSX 24.1 2,965 26.7 3,244 61,196 2.255
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Old 02-09-2011, 23:02   #11
W.E.G.
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double-tap

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Old 02-09-2011, 23:08   #12
W.E.G.
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.223 Remington vs. 5.56: What’s In a Name


By BRYCE M. TOWSLEY field editor
American Rifleman – September 2007


Most gun guys know the history of the .223 Remington and that it - like so many of our popular cartridges - started life in the military. Because the military switched to metric designations sometime in the 1950s, this little .22-cal. cartridge was later called the 5.56x45 mm NATO (commonly referred to as "5.56x45 mm").

The 5.56x45 mm surfaced in 1957 as an experimental cartridge in the AR-15 rifle. The concept was to develop a smaller, lighter military cartridge that would still be traveling faster than the speed of sound at 500 yds., and this was accomplished by using a 55-gr. boattail bullet. The AR-15 evolved into the select-fire M16 rifle that was adopted by the military in 1964.

Even though it would ultimately kill off its own .222 Rem. and .222 Rem. Mag. cartridges, Remington was quick to act, and very shortly after the military adopted the 5.56x45 mm cartridge the firm brought out the civilian version, called the .223 Remington. Confusion followed.

The common misconception is that the two are the same; that 5.56x45 nun and .223 Rem. are the same dance partner, but with a different dress. This can lead to a dangerous situation. The outside case dimensions are the same, but there are enough other differences that the two are not completely interchangeable.


One big difference is pressure. It becomes a bit confusing, as the pressure for the two is not measured in the same way. The .223 Rem. is measured with either Copper Units of Pressure (c.u.p.) or-more recently-with a midcase transducer in pounds per square-inch (p.s.i.). The military 5.56x45 mm cartridge is measured with a case mouth transducer. The different measuring methods prevent a direct comparison, as a case mouth transducer gives lower numbers on identical ammunition when compared to those from a midcase transducer. That's because the pressure is measured later in the event, after the pressure has already peaked. According to Jeff Hoffman, the owner of Black Hills Ammunition, military ammunition can be expected to hit 60,000 p.s.i., if measured on a Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) mid-case system. Black Hills loads maximum average pressure is 55,000 p.s.i., while a 5.56x45 mm measured with a case mouth transducer has a maximum average pressure of 58,700 p.s.i.

While the 5.56x45 mm chamber is slightly larger than the .223 Rem. chamber in just about every dimension, the primary difference is throat length, which can have a dramatic effect on pressure. The 5.56x45 mm has a longer throat in the chamber than the .223 Rem. The throat is also commonly called the leade, which is defined as a portion of the barrel directly in front of the chamber where the rifling has been conically removed to allow room for the seated bullet. Leade in a .223 Rem. chamber is usually 0.085", while in a 5.56x45 mm chamber the leade is typically 0.162", or almost twice as much as in the .223 Rem. chamber. Also, the throat angle is different between the two chambers, and that can affect pressure rise and peak pressure.

SAAMI regulates cartridge overall length, but not bullet ogive design. The shape of the ogive can significantly affect how far the bullet jumps before contacting the rifling. Some 5.56 mm bullets have an ogive suitable for 5.56 chambers with the longer throat, but if they were chambered in a .223 Rem., it could result in very little, if any, "jump" to the rifling. This can increase pressures. Remember, the 5.56x45 mm already starts out at a higher pressure. If the higher-pressure 5.56x45 mm cartridge is then loaded into a .223 Rem. firearm with a short throat, the combination of the two factors can raise chamber pressures.

If you are a handloader, you must also consider that the 5.56x45 mm cartridge case may have a thicker sidewall and a thicker head, which were designed to withstand the stresses generated by the higher chamber pressures. This reduces the powder capacity of the case. If the 5.56x45 nun case is reloaded with powder charges that have proven safe in .223 Rem. cases, this reduced internal capacity can result in much higher chamber pressures.

Bottom line? It is safe to fire .223 Rem. cartridges in any safe gun chambered for 5.56x45mm. But, it is not recommended and it is not safe to fire 5.56x45 nun cartridges in a firearm chambered for .223 Rem.

In fact, the 5.56x45 mm military cartridge fired in a .223 Rem. chamber is considered by SAAMI to be an unsafe ammunition combination and is listed in the "Unsafe
Arms and Ammunition Combinations" section of the SAAMI Technical Correspondent's Handbook. It states: "In firearms chambered for .223 Rem. - do not use 5.56x45 mm Military cartridges."

There is no guarantee, however, that .223 Rem. ammunition will work in 5.56x45 mm rifles. Semiautomatic rifles chambered for 5.56x45 mm may not function with .223 Rem. ammunition because they are designed to cycle reliably with the higher pressure and heavier bullets of the 5.56x45 mm particularly with short barrels. While problems are rare, they do not indicate that the ammunition or rifle are defective. Like some marriages, they are simply incompatible.

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.

Another issue is the twist rate of the rifling. The SAAMI specification for .223 Rem. is a 1:12" twist, and most non-AR-15-type rifles will use that rate. But, this is a cartridge that crosses a wide spectrum of uses, and as a result there is often a wide deviation from the 1:12" twist rate, particularly in the very popular AR-15-style "black guns." There are bullets available for the .223 Rem. that range in weight at least from 35 grs. to 90 grs. With that wide of a spectrum, one twist rate is not going to be enough.

Firearms chambered for 5.56x45 mm often have a rifling twist rate of 1:7" to stabilize the long, sleek, heavy bullets used in long-range shooting. Any rifle with a 1:7" twist rate will work best with bullets heavier than 60 grs.

On the other hand, a 1: 12 twist rate (most bolt-action .223 rifles) will stabilize most bullets up to 60 grs., however some longer 60-gr. bullets will not shoot well with that twist rate. Many firearms use a 1:9" twist, which is a very good compromise that works well with most bullets up to 70 or 75 grs. The great thing is that if you have a good barrel and quality bullets, the 1:9 works well with even the lightest bullets.
What does all this mean? If you have anAR-15 type firearm with a 5.56x45 mm chamber you can shoot either .223 Rem. or 5.56x45 mm safely. If your twist rate is 1:7" you should use bullets weighing 60 grs. or heavier. If you have any rifle with a 1:12 twist you should shoot bullets of 60 grs. or less for best accuracy. If you have a .223 Rem. rifle of any type, it is not recommended that you use 5.56x45 mm ammunition.

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Old 02-10-2011, 11:58   #13
Gunnut 45/454
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And where is this published? What reloading manual?
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Old 02-10-2011, 18:37   #14
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My rifles are all chambered for 5.56MM. I have 2 Colt LE6920 rifles and 1 MK12 MOD1.

All rifles have a 1:7 twist rate. The Colts have a chrome lined barrel and the MK12 has a stainless barrel (No lining). LE6920s have a 16" barrel while the MK12 has an 18" barrel.

I have shot 7 different loads through each of the rifles.

PPU M193 (5.56MM)
PPU M855 (5.56MM)
Hornady TAP 75 Gr. OTM (.223)
Black Hills 75 Gr. OTM (.223)
Black Hills 77 Gr. OTM (.223)
Black Hills 69 Gr. OTM (.223)
MK262 MOD1 (5.56MM)

Comparing all but the M855 and M193…all of the loadings gave me MOA out of the MK12. There was absolutely no difference in accuracy between the .223 and 5.56MM loads.

Out of the LE6920s I also got MOA. No difference was noticed in accuracy.

Muzzle velocity was a different story. The 5.56MM ammunition had about 100-200 FPS faster chrono speeds out of the rifles tested.

Personally I would stick with .223 ammunition. It's easier to get and (USUALLY) more abundant. The MK262 ammunition I use is hard to come buy. I buy by the case when it comes in and that isn't very often. I like the Black Hills 77 Gr. OTM out of all of the listed loads sans the MK262. That is my most favorite.

Last edited by SIGShooter; 02-10-2011 at 18:37..
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Old 02-10-2011, 18:43   #15
mboylan
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mboylan
And where is this published? What reloading manual?
Just go to the Ramshot web site. There is a pdf with all of their load data.

http://www.ramshot.com/powders/loadguide/Ramshot4.5.pdf

There's more out there too.

...they also assume identical dimensions between 5.56 and .223

Check:
http://www.ask.com/wiki/5.56x45mm_NATO

http://www.ask.com/wiki/.223_Remington?qsrc=3044

Both maximum case lengths are set to 1.760. I would heed that if loading to 62,000+ PSI.

Most of the service rifle guys trim to about 1.754.

Last edited by mboylan; 02-10-2011 at 19:14..
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