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Old November 27, 2012, 06:30 PM   #1
BigTex308
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5.56 vs .223

I hoping yall can settle a debate between me and a friend...


I'm sayin that you're not supposed to fire 5.56 in a rifle chambered in .223 but you can fire .223 in one chambered in 5.56. The reason being that the 5.56 has more powder and runs at higher pressures.

He is saying that the 5.56 has a thicker case and therefore should hold less powder.

Any clarification?


Also.....


Isn't it true that you can fire a 7.62x51 in a .308, but you shouldn't fire a .308 in a 7.62x51?



Thanks in advance



Ike




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Old November 27, 2012, 06:37 PM   #2
JimDandy
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I dunno about the .308 but you are correct that 5.56 does not go in .223 though .223 can go in 5.56. The reason why is up for debate, though the two I stick with is A)Because SAAMI says so, and B) the best logic I heard was the walls were thicker and created higher pressure, which doesn't necessarily require more powder. But truth be told, I don't know why, other than the experts say it's bad.
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Old November 27, 2012, 06:55 PM   #3
plouffedaddy
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Quote:
I hoping yall can settle a debate between me and a friend...


I'm sayin that you're not supposed to fire 5.56 in a rifle chambered in .223 but you can fire .223 in one chambered in 5.56. The reason being that the 5.56 has more powder and runs at higher pressures.

Correct. 556 also has different taper/throat dimensions.

He is saying that the 5.56 has a thicker case and therefore should hold less powder.

He's wrong about the thicker case=less powder debate because the dimensions are not the same.

Any clarification?






Thanks in advance



Ike
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Old November 27, 2012, 07:03 PM   #4
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Quote:
>> ...the 5.56 has more powder and runs at higher pressures.
FOR UNCLE NICK:

Would, in fact, a NATO round loaded to 62kpsi by Europe's C.I.P. setup, measure that same pressure by SAAMI test standards?
Or would SAAMI tests show it to produce far less than 62kpsi>
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Old November 27, 2012, 10:57 PM   #5
Metal god
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It's my understanding that it's all about the lead/throat . A 5.56 chamber/barrel has a longer lead/throat then the 223 . This allows room for the longer heavier NATO rounds like tracers , green tip and others .Remember we are talking about NATO ammo made in many countries . There are some 5.56 NATO rounds that if put in to a 223 chamber the bullet would be pushed in to the lans of the rifling . When a gun is fired with the bullet slightly pushed into the rifling , this can create a pressure spike well above recommended levels . It's my understanding just a little lead ( fractions of an inch ) can make a big difference of pressure inside the chamber .

Again thats my understanding and it may not be fact . Any corrections are welcome
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Last edited by Metal god; November 28, 2012 at 06:43 AM.
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Old November 28, 2012, 09:07 AM   #6
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Quote:
I'm sayin that you're not supposed to fire 5.56 in a rifle chambered in .223 but you can fire .223 in one chambered in 5.56. The reason being that the 5.56 has more powder and runs at higher pressures.

He is saying that the 5.56 has a thicker case and therefore should hold less powder.

Any clarification?
Pressure difference is insignificant.

NATO brass may be thicker but you have to measure the volume of water each case holds to know if it holds more or less powder.

It's about the leade, or the amount of free bore from the tip of the bullet to the beginning of the rifling. "Theoretically" a longer/heavier 5.56 round could possible be too long for a .223 chamber. If the bullet is jammed into the rifling when chambered it may result in a over pressure when fired.

People have been shooting 5.56 in .223's for years and I have not found any documented cases of a failure from this.





Quote:
Isn't it true that you can fire a 7.62x51 in a .308, but you shouldn't fire a .308 in a 7.62x51?
NO. There is a very small difference in max head space between the two chambers, .002-.004". Either chamber well fire either round. Pressure differences are insignificant.

Read FALphil's excellent paper on the difference, it's a sticky here someplace.
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Old November 28, 2012, 09:27 AM   #7
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223 in 5.56 or 5.56 in 223????


It depends, it its a "pre-internet" gun it doesn't matter.

Only guns made after internet gun forums became popular are effected.

Same with the 7.62 in 308 or 308 in 7.62.
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Old November 28, 2012, 09:30 AM   #8
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Before the internet they were the same.
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Old November 28, 2012, 12:17 PM   #9
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So if I were to get a good supply of 5.56 Lake City brass, since I full size and trim the cases back to just below factory spec of the .223 Rem then they should be fine.

My R-15 says .223 Rem NOT .223/5.56.
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Old November 28, 2012, 12:33 PM   #10
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Here we go again. Let's see if someone wins this time around.

Powder/case capacity—forgedaboudit.
Pressure—forgedaboudit.
Shorter lead to throat—maybe. Just don't shoot the heavy/longer rounds. 55gr fmj/bt/ will be fine.

It turns out that NATO 5.56 is more pricey now anyways, so why shoot it in .223 when there are more accurate, cheaper .223 offerings.

.308/7.62—This is different and significant I believe (of course I might be wrong). It depends on origins of the barrel. Some European 7.62 projectiles are "correctly" dimensioned at .312 OD—correct because the rifle grooves are actually 7.92—and may hurt a .30 rifle made for .308 projectiles.

If you're just using the brass this is a moot point... because you have worked up your loads accordingly. Full-Length/Small-Base/Neck sizing... it doesn't matter, it's up to you and what works well in a given rifle. Do it right per the books and watch for pressure signs.

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Old November 28, 2012, 07:31 PM   #11
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I do not want to be a "fly in the ointment", but I have used .223 rem as big as 72 grains. And I mean bought over the counter, commercial ammunition.Where does that put the lead/throat issue?

Mind you, I have heard and believed the same thing, it's just hindsight/experience rearing it's ugly head.
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Old November 28, 2012, 07:36 PM   #12
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Quote:
I have used .223 rem as big as 72 grains
Try 90 gr bergers. They work great in a fast twist AR and Bolt gun.
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Old November 28, 2012, 09:56 PM   #13
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I think and I must emphasize THINK that it's 5.56 NATO that's the issue .

Meaning
( Im not sure on the numbers but im going to put some out there just for example )

You have 20 different countries with who know's how many manufacturers in each of those countries making the same product .I would expect that not all the ammo would be manufactured to the exact same tolerances . My guess is the 5.56 chamber has a longer lead/throat to make sure no mater what country your getting your ammo from it will shoot safely and reliablely .
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Old November 29, 2012, 06:59 AM   #14
Bart B.
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Sweetshooter, where in the dickens did you get a basis for this:
Quote:
.308/7.62—This is different and significant I believe (of course I might be wrong). It depends on origins of the barrel. Some European 7.62 projectiles are "correctly" dimensioned at .312 OD—correct because the rifle grooves are actually 7.92—and may hurt a .30 rifle made for .308 projectiles.
I ask 'cause the 7.62 NATO round's (as well as the .308 Win.) barrel was originally spec'd at .3000" (7.620mm) for bore and .3080" (7.823mm) for groove diameter. The USA's SAAMI bullet diameter spec is .3090" -.0030" (7.849mm -.076mm) and the MIL-SPEC's the same as far as I can determine. Actual bullet diameter's been in the .3070" (7.798mm) to .3092" (7.854mm) range for both commercial and military versions.

Many thousands of Lapua's .3092" diameter 170, 185 and 195 grain FMJRB bullets have been fired in .308 Win. barrels with .299" bore and .3075" groove diameters without incident using max loads. 42 grains of IMR4064 under their 185-gr. version has been used winning many a match setting a few records and it may well be the most accurate load ever tested I know about for the .308 Win. Military rifle teams shooting 7.62 NATO handloaded match ammo at proof load pressures in the 65,000 CUP (80,000 PSI) range in their M1's and M14's never had a safety issue, but I wouldn't recommend such loads in bolt guns.

I've never heard of any 30 caliber bullet nor a 7.62/.308 barrel groove diameter at .312" (7.925mm) diameter. . . .that is until I read your post.

For SAAMI specs:
http://www.saami.org/specifications_...wnload/206.pdf
Pressure and velocity specs start on page 13; find the .223 Rem. & .308 Win. data. .223 Rem. chamber and barrel specs are on page 47. Page 66 has the info on the .308 Win. barrel and chamber dimensions.

For MIL-SPECS for the 7.62 NATO M80 round:
http://www.everyspec.com/MIL-SPECS/M...-46931F_42098/

MIL-SPECS for the 5.56 NATO M193 round:
http://www.everyspec.com/MIL-SPECS/M...C-9963F_25766/

Open the file then go to section 3.7.1 for pressure.

Regarding any pressure number for these cartridges. The SAAMI document explains in detail how their CUP and PSI pressure systems are configured. I don't know if the MIL-SPEC systems are the same. Identical ammo and barrels will get different pressure numbers depending on where the sensor is positioned relative to the cartrige.

Last edited by Bart B.; November 29, 2012 at 08:34 AM.
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Old December 1, 2012, 02:11 AM   #15
Sweet Shooter
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I got that from Ceska Zbrojovka. I shoot a CZ 7.62x39 bolt gun that had a bore (across the grooves "ID") of .312 not .308. It's true. America doesn't always get to call the shots. Apparently.

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Old December 1, 2012, 08:35 AM   #16
mehavey
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Quote:
Originally Posted by BART B
MIL-SPECS for the 5.56 NATO M193 round:
http://www.everyspec.com/MIL-SPECS/M...C-9963F_25766/
PUBLICATIONS
SCATP-5.56 - Ammunition Ballistic Acceptance Test Methods,
Test Procedures for 5.56mm Cartridges....

3.7 Chamber pressure.

3.7.1 Measurement by copper-crush cylinder.
-The average chamber pressure of the sample cartridges, conditioned
at 70° ± 2°F, shall not exceed 52,000 pounds per square inch (PSI).
The average chamber pressure plus three standard deviations of chamber
pressure shall not exceed 58,000 PSI.

3.7.2 Measurement by piezoelectric transducer.
-The average chamber pressure of the sample cartridges, conditioned
at 70° ± 2°F, shall not exceed 55,000 PSI. The average chamber
pressure plus three standard deviations of chamber pressure shall
not exceed 61,000 PSI.


Well.... finally we have apples and apples..... and it turns out SAAMI's 55,000 (true) psi is good2go
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Old December 1, 2012, 09:39 AM   #17
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A popular SAAMI myth concerns brass thickness of military 5.56mm cartridge cases. SAAMI says military cases are thicker than commercial .223 cases. i've weighed thousands of cases since 1968: US 5.56mm military cases are not thicker.

Some Brit military cases are thicker than US military cases. The thickest cases of all are Lapua; one must be careful when reloading those.

Click on brass weights comparison:

http://ar15barrels.com/tech.shtml
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Old December 1, 2012, 10:42 AM   #18
mehavey
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Quote:
SAAMI says military cases are thicker than commercial .223 cases.
I was unaware that SAAMI had taken that as an official position in 223/5.56 comparison.
Is there a primary source from SAAMI on that?

FWIW:
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Old December 1, 2012, 11:16 AM   #19
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When I studied this topic I concluded that much of the confusion lies in the subject, which oscillates between being the cartridge and the chamber.

I also contacted two manufacturers of .223 REM bolt action rifles, Browning and CZ. I asked if you could shoot 5.56 NATO in their rifle. Browning said NO. CZ said YES.
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Old December 1, 2012, 02:27 PM   #20
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I asked if you could shoot 5.56 NATO in their rifle. Browning said NO. CZ said YES.
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Simply a CYA thing for Browning in the very rare event smething bad. There are very minor differences between some 5.56 rounds and some 223 rounds. Same with some 223 rifles and 5.56 rifles.

What most people don't realise is that you will see just as much variances between different brass, ammo and rifle chambers in any other chambering. Often a Remington 270 chamber will vary slightly from a Winchester chamber. You will find that at times Federal 270 ammo is loaded to very differnt pressures than Hornady 270 ammo and with slightly different brass specs.

But since we have 2 names for the same cartridges in 223/5.56 as well as 308/7.62X51 it causes confusion. You may well run into a rare 223 rfle that will give issues with some 5.56 ammo. But you are just as likely to run into a 270 rifle that has the same problems with some 270 ammo and not other 270 ammo.
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Old December 1, 2012, 03:10 PM   #21
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What most people don't realise is that you will see just as much variances between different brass, ammo and rifle chambers in any other chambering. Often a Remington 270 chamber will vary slightly from a Winchester chamber. You will find that at times Federal 270 ammo is loaded to very differnt pressures than Hornady 270 ammo and with slightly different brass specs.
This is my point exactly . You have one country making a slightly longer 5.56 round and a gun maker making a slightly smaller 223 chamber/lead/throat . This is when you get the pressure spike
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Old December 1, 2012, 07:21 PM   #22
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Funny how people make it out to be such an issue you would think there was thousands of .223's in the scrap metal pile cause 5.56 ammo blew them to smitherines.....


Well where they at?????? Yeah I thought so.
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Old December 1, 2012, 08:45 PM   #23
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I was unaware that SAAMI had taken that as an official position in 223/5.56 comparison.
Is there a primary source from SAAMI on that?
Several years ago SAAMI had that thick case warning on their site.
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Old December 1, 2012, 09:28 PM   #24
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Funny how people make it out to be such an issue you would think there was thousands of .223's in the scrap metal pile cause 5.56 ammo blew them to smitherines.....


Well where they at?????? Yeah I thought so.
Bingo!!!

I've fired at least 250,000 rounds of 5.56mm ammo in my .223 rifles since 1968. All my guns are still working.

Strange that SAAMI came out with their dire warning about the time millions of 5.56mm cartridges hit the market. In this lawyer run society few gunmakers, gun writers, panjandrums or experts are going to say SAAMI is wrong.

There are a number of different .223/5.56mm chambers, at least one dozen of them. A gunsmith tells me no US maker he is aware of chambers guns using a SAAMI spec reamer. .223/5.56mm rifles have become wildly popular.

For most shooters there is no way of knowing for sure what kind of chamber the gun has. It could be a very tight chamber or a huge sloppy one. Some companies regrind their reamers. Most of the those rifle barrels are not chambered by machinists or skilled technicians. Theres a race to the bottom in salaries: Unskilled labor does much of that work. i've seen out of round chambers, off center chambers and bulged chambers(in NEF guns).

i'm not telling anyone what to shoot in the chamber of his/her gun. i've saved oodles of money by using surplus 5.56 ammo in my guns. I'm an EOD guy; much of it was free.

Until recently very few had pressure tested 5.56mm ammo fired in .223 chambers. What you have been told may not be true.

http://www.luckygunner.com/labs/5-56-vs-223/
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