Caliber question.308/ 7.62 NATO

[igotta40]

A question for the forum- is there a difference between the two subject calibers, as there is with .223 Remington/ 5.56 x 45 NATO?

 

[MTMilitiaman]

 

[Bart B.]

Yes, there's a difference. Not much, but enough that military ammo may cause a problem in commercial ones; SAAMI says not to shoot MIL SPEC 5.56 ammo in SAAMI spec .223 Rem chambers.

Again, the error in military arsenals using PSI numbers for pressure instead of CUP that their systems used in the early 1950's shows up (the graphics above listing pressures) and confuses lots of folks.

SAAMI specs for the 308 Win peak average pressure is 52,000 cup; 62,000 psi. Winchester's cup systems were a bit different than Frankfort Arsenal's that were used in the NATO round development using 300 Savage cases to start with.

MIL SPEC pressures for the 7.62 NATO were 50,000 cup originally, about 60,000 psi using modern transducer piezo systems today.

Another error is where headspace reference at the case and chamber shoulder is indicated. That's about .345" on the case neck; actual point is about half way up the shoulder to a reference diameter of .400".

Here's the facts:

http://forums.thecmp.org/showthread.php?t=146769

http://ammunitionstore.com/content/223 Remington.pdf

http://ammunitionstore.com/content/5.56×45mm NATO.pdf

 

[igotta40]

OK thanks guys, good info. I have six rifles chambered for the .308 Winchester, none for the NATO specific. Two M1A, two scout rifles, Savage Axis, M1 Garland (CMP)

 

[FL-NC]

Military rifles I've shot don't seem to think so. Neither doesmy 1 civilian 308- a Ruger American.

 

[igotta40]

Garand- auto correct.....

 

[igotta40]

FL-NC, I have a Ruger American Navy digital camo in .270 WIN.
I don't see why they don't offer it in .308

 

[Varminterror]

I'm not sure where the graphic from @MTMilitiaman's post might have originated, but the pressures represented are not correct. It's confusing the old 50,000 CUP standard with a new 60,190psi 62,000psi standards. Here's a quote from another site, WITH LINKS TO READ STRAIGHT FROM THE HORSE'S MOUTH for SAAMI, CIP, and NATO EPVAT.

The highlights:

1) There is no difference by NAME between 308win and 7.62x51mm except for in NATO designations, as both SAAMI and CIP use 308 Winchester as the primary filing name, and 7.62x51mm as additional names - registered in both.

2) The pressure is almost identical for both SAAMI and CIP/NATO - 62,000psi vs. 60,190psi. Recall, both test maximum average pressure, so a difference of 1,810psi really isn't significant in terms of real world rifles. Any difference is merely a technicality.

3) Factory loads which are compliant to the LOWEST level of the 3 standards (SAAMI, CIP, and NATO EPVAT) will be compliant for all 3. Those compliant with the HIGHEST, of course, are only compliant with the highest - which is SAAMI. Manufacturers can choose to make their lives easier by down loading their "saami compliant loads" to be "CIP compliant" as well, and put the same load in two different boxes.

There DO EXIST three pressure and chamber standards for 308win/7.62x51mm.

CIP, SAAMI, and NATO EPVAT (which also shares reciprocity with CIP compliance)

CIP = Commission internationale permanente pour l'épreuve des armes à feu portatives In English, that's basically: "Permanent International Commission for the Proof of Small Arms" - This is the regulatory body worldwide, and most importantly, this is who NATO looks at for ammunition standards.

CIP Standard for 308 Winchester = 4150 bar, which is 60,190psi


CIP standard list - includes 308win in Tab 1-Rimless cartridges (might have to search for it at the top)

SAAMI = Sporting Arms and Ammunition Manufacturers Institute - This is the voluntary compliance proof registration body in the USA

SAAMI standard for 308 Winchester = 62,000psi


SAAMI standard list - includes 308win on page 43

NATO EPVAT = North Atlantic Treaty Organization Electronic Velocity and Action Time - this is the certifying standard for NATO approved ammunition. In lieu of direct EPVAT barrel testing, ammunition manufacturers CAN get NATO acceptance by complying to CIP standards

7.62 mm. STANAG 2310 and NATO Manual of Proof and Inspection AC/225 (LG/3-SG/1) D/9

NATO EPVAT standard for 7.62 NATO = 415.0 Mpa which is 60,190psi But the measurement position is ahead of the case mouth, which differs from the testing methods used by CIP & SAAMI. However, NATO EPVAT does accept approved CIP compliance as qualification.

The important things:

• Both CIP and SAAMI call the cartridge "308 Winchester" with 7.62x51mm as an interchangeable name. This is different than the 223/5.56 cartridges where US Customary vs. Metric nomenclature delineates two different cartridges within these commissions. So the name on the box actually doesn't really matter for their standards. For NATO EPVAT, 7.62x51mm, or more officially 7.62 NATO is the the official nomenclature used, no 308win anywhere. BUT - commercial ammunition labeled as 7.62x51 or 7.62 NATO are not necessarily certified as NATO EPVAT compliant unless branded as such with the NATO Circled Cross on the headstamp.

• SAAMI compliance is voluntary, nobody is required to submit their ammunition for testing. NATO EPVAT testing is only required (if CIP is not met) if you want to contract to NATO country military service, nobody is required to meet that standard for commercial/civilian ammunition. No maker in the US is required to submit to CIP. So technically, ammo on the shelf does NOT have to be 62,000psi proven, or 60,190psi proven. It could be anything the ammunition manufacturer wants it to be, higher or lower.

• Foreign made stuff, if it's compliant with anything at all, regardless of 308win or 7.62x51 on the box, will almost always be CIP compliant, not SAAMI, meaning it's loaded to lower pressure than USA manufactured ammunition COULD be loaded.

• Even though the same maximum pressure is listed for CIP & NATO EPVAT, they do not use the same position in the barrel for their respective tests, so the same maximum pressure does not necessarily represent exactly the same operating pressure curve, or even interchangeable maximum pressure.

• SAAMI, or CIP, compliant loads are not necessarily loaded to the Maximum Allowable Pressure standard, but are only assured to be beneath it. So it's very common for ammunition manufacturers to produce a CIP or NATO compliant load (which ever ends up the lowest of the 2), then have it tested and labeled as compliant for all 3. Being under the lowest qualifies for all 3. This also saves production cost for the manufacturer.

• Unless it has a NATO Circled Cross, it's a safe bet it's not been EPVAT tested, nor approved, so if it's foreign, it's likely CIP standard, if it's US, it's likely SAAMI

 

[HankB]

. . .
2) The pressure is almost identical for both SAAMI and CIP/NATO - 62,000psi vs. 60,190psi. Recall, both test maximum average pressure, so a difference of 1,810psi really isn't significant in terms of real world rifles. Any difference is merely a technicality. . . .

Are the SAAMI and CIP methods for measuring pressure identical? I vaguely recall reading that, years ago, SAAMI moved from copper crushers to conformal piezo transducers, but CIP was still using a modified case with a hole drilled in the side so the gas would impinge on a channel sensor. The numbers, though close, would not be expected to be precisely identical.

 

[jmr40]

Basically 5.56 and 7.62 are military designations for commercial 223 and 308. Military 5.56 CAN be loaded hotter than commercial 223 and MIGHT cause problems if fired in 223 chambers. Might not. It is generally advised that rifles stamped 5.56 can handle both but many discourage firing hotter 5.56 in 223 marked chambers. But other than unreliable extraction and ejection in semi-autos I've yet to hear about any real problems from those who do so, and many do. Never known or heard of a problem in a bolt gun and 223 chambered semi-autos aren't exactly common.

It is the other way with 7.62 and 308. Commercial 308 can, and often is loaded hotter than military 7.62 ammo. I've never known or heard of military 7.62 ammo causing a problem in 308 rifles. But the hotter 308 can cause extraction and ejection problems in semi-autos designed to work at 7.62 pressure.

 

[Varminterror]

Different equipment is used for CIP and SAAMI testing. SAAMI uses piezo sensors which fit the case wall, whereas CIP uses a channel sensor which must be exposed via a drilled port in the case wall. The difference is largely trivial, but remains a difference nonetheless. I've oft heard it said the difference in the two standards is only due to this equipment difference, however, I have never heard/read of any actual testing done to confirm truth if you were to test a lot of the same ammo on both, you'd get this constant offset.

The fact remains, if your rifle is sensitive to a difference so small, then one round out of a standard batch of ammo would destroy it just as soon as would a CIP vs. SAAMI mix up.

The NATO EPVAT standard, alternatively, places the piezo sensor in front of the case mouth, which I believe is another channel sensor if my memory serves correctly. I expect any difference here compared to the other two methods remains also to be purely academic, a distinction without a difference, since peak pressure is not obtained while the bullet remains in the case, therefore the chamber area and case mouth area during the moment of peak pressure should be exposed to significantly equal pressure.

 

[Bart B.]

Page 158 in the following SAAMI document starts the section that explains their velocity and pressure testing. Diagrams show how their two different systems are used on each of many cartridges.

http://www.saami.org/specifications_and_information/publications/download/Z299-4_ANSI-SAAMI_CFR.pdf

 

[RecoilRob]

For gas operated rifles the maximum pressure differences might very well be insignificant, but the port pressures can vary a lot and the 308's often have higher enough to cause harsh cycling in NATO designed systems. Bolt guns don't matter so much as long as the chamber throat can allow full release of the projectile during firing.

This is the biggest thing I've noticed on 5.56 vs .223....resize and check a bunch of once-fired 5.56's and you'll very likely need to trim every single one of them due to very long necks. I don't think this came from stretching...but more that they added a bit of material to allow for a firm crimp on the military ammo as the trimming normally just removes what had been the crimp. In a tight .223 chamber this material might have no where to go when trying to release the projectile and can lead to excessive pressure.

 

[Bart B.]

For gas operated rifles the maximum pressure differences might very well be insignificant, but the port pressures can vary a lot and the 308's often have higher enough to cause harsh cycling in NATO designed systems.

The opposite of that was the case when M1's were first rebarreled to 7.62 NATO.

Springfield Armory arsenal made the first 7.62 NATO barrels for Garands using the same port size as 30-06 barrels. The USN Match Conditioning Unit in San Diego quickly learned the lower port pressure the NATO rounds produced was insufficient to reliably cycle the action. The ports were drilled out from about .080" to about .110" and that solved the problem. M14 gas ports are several inches closer to the chamber than M1 ports.

 

[jonnyc]

Winchester worked with the Ordnance Dept. to produce the 7.62x51 cartridge. They were then allowed to market it as the .308W. They are the same, just as your mother's sister is your aunt. Some commercial chambers are made tighter for accuracy, and there are a lot of producers who make military 7.62x51 ammo, so you are bound to find some manufacturer variances that cause difficulties for military ammo in commercial chambers. Some military 7.62 has thicker internal webs to withstand machine-gun extraction. You need to exercise care when reloading those cases to maximum commercial recipes.
In short; they are the same thing and perfectly interchangeable in factory loadings.
Any comments above to the contrary (or following) simply show that the poster knows nothing of the history of the round. This is an old "controversy" and was settled long ago.

 

[RecoilRob]

In short; they are the same thing and perfectly interchangeable in factory loadings.
Any comments above to the contrary (or following) simply show that the poster knows nothing of the history of the round. This is an old "controversy" and was settled long ago.

Except when it comes to gas guns and the required port pressures needed to run them positively but without excessive velocity which can lead to battering and breakage. 7.62 Nato ammo will deliver the particular port pressure that the M-14 is designed for...while some commercial 308 W is loaded with much slower burning powders that will have the port pressures far in excess of that designed value. An adjustable gas plug is a good idea on an M1A/M14 if commercial ammo is to be used IMHO so you can tailor the action energy to the load rather than the load to the action.

 

[jonnyc]

Fine, but that's simply a difference in loadings of the round, not different cartridges.

 

[Bart B.]

Best writeup on the origin of the 308 Win cartridge. Verified by a friend who worked at Aberdeen Proving Ground in kahoots with Frankfort and Lake City ammo plants.

https://thefiringline.com/forums/attachment.php?attachmentid=39835&d=1229900860

From what I've gleaned from good sources, Winchester's only help in 7.62 developenent was the same as Remington's. Both sold thousands of 300 Savage cases to Frankfort Arsenal to be resized different ways for tests. Winchester got the first civilian contract to produce 7.62 ammo.

 

[RecoilRob]

Fine, but that's simply a difference in loadings of the round, not different cartridges.

Yes...the CASES are the same external dimensions, but when you tell someone that "they are the same thing and perfectly interchangeable in factory loadings" that is not the case. The factory loadings ARE different enough to cause issues in military gas guns that are best avoided. Particularly the 308 Hornady Light Magnum which launches the 150 grain bullet at about 3000 fps...which is a good 250 faster than a NATO round yet does it without exceeding the same maximum chamber pressure. Using such a thing in a stock M1A could lead one to damaging their rifle in time. This is the distinction I was trying to illuminate.

 

[Varminterror]

Yes...the CASES are the same external dimensions, but when you tell someone that "they are the same thing and perfectly interchangeable in factory loadings" that is not the case. The factory loadings ARE different enough to cause issues in military gas guns that are best avoided. Particularly the 308 Hornady Light Magnum which launches the 150 grain bullet at about 3000 fps...which is a good 250 faster than a NATO round yet does it without exceeding the same maximum chamber pressure. Using such a thing in a stock M1A could lead one to damaging their rifle in time. This is the distinction I was trying to illuminate.

Read the links in the quote I posted above. There is NOTHING about NATO EPVAT testing methodology which confirms port pressure. There are two ways to get that 7.62 Circled Cross, 1) pass through NATO EPVAT testing, or 2) Pass through CIP testing, which is an approved alternative in NATO EPVAT. In either case, the port pressure is NOT measured. NATO EPVAT tests just in front of the case mouth, CIP tests pressure at a position within the case wall itself.

So while there is certainly an opportunity for certain slower burning loads to run a later peak and higher port pressure, none of the 3 testing methodologies tests for port pressure, and all 3 are just as likely to have a COMPLIANT LOAD damage an operating rod.

A shooter should be cognizant of the design implications of their platform, and a reloader should be especially mindful of such, however, when it comes to the methods used for approved ammunition for SAAMI, NATO EPVAT, or CIP, port pressure is NOT a consideration. Within a given ammunition "model," as long as the right bullet leaves at the right velocity, and satisfies the pressure standards, it will pass NATO EPVAT, and will satisfy contract terms for the respective ammunition order. In my view, it's really only the ammunition requirements which come anywhere close to a port pressure restriction, as the expectations for bullet and MV narrow the options for powder selection and charge weight a great deal.

What I generally consider - SAAMI, CIP, and NATO EPVAT all establish MAXIMUMS for pressure, but there is nothing to require a manufacturer to load to any respective maximum. We often see this in 454Casull cartridges, as an example - factory loads often run somewhere in the 50kpsi ballpark, instead of the 65,000psi SAAMI max. Why? Well, because at 65kpsi, crimp jump can become a problem, and at 50kpsi, the bullet is still going to do the job on the business end just fine. Most consumers will never notice the difference, nor care if they ever did discover this offset. Equally, there are plenty of factory loads which supersede .mil loads for 308/7.62, but functionally, the difference at range just isn't that great, so there's no reason to push the envelope. In the consumer market, on the other hand, if a certain load runs 100-250fps faster with the same bullet weight, and you slap some marketing term like "high velocity, Light Magnum, Super performance," etc etc on the box, you can charge a premium AND PEOPLE WILL PAY IT. So there is much more motivation to push velocities and tweak pressure curves for commercial market ammunition. Soldiers get told what they will shoot, civilians have the option of choice - so one will always remain to push the ragged edge of pressure standards, the other will always remain to be where it has been for decades.

 

[wally]

In todays lawsuit happy environment if there was any significant difference between .308 and 7.62x51 or .223 vs. 5.56 that was a safety issue the lawsuits would be flying. I'm still waiting for verified examples of .223 guns damaged by shooting 5.56 or vice-versa, same for .308 vs 7.62 -- ignoring gas system issues from using inappropriately hot ammo.

 

[RecoilRob]

So while there is certainly an opportunity for certain slower burning loads to run a later peak and higher port pressure, none of the 3 testing methodologies tests for port pressure, and all 3 are just as likely to have a COMPLIANT LOAD damage an operating rod.

.

Yes....the NATO specs for pressure do NOT dictate any particular port specs...but DO have a velocity requirement of 2750 @ 78ft. So if a loading doesn't exceed the maximum pressure nor exceed the velocity...it meets spec. I can't find how much tolerance is given on the velocity measurement so can we assume that 2750 is the maximum? If so...there are only a limited number of powders that would meet the requirements without exceeding either pressure or velocity.

Remember the problems that the British Radway Green 5.56 NATO had in our US guns...being as it had been loaded specifically to run the pitiful early Enfield L85's. It uses a compressed charge yet runs over 100 fps slower than US M855 which seems to indicate that the port pressure would be lower, and my Bushmaster Varminter won't reliably eject with it. The Colt Carbine eats it up as well as a PLR-16, so it's just the rifle length gas system which is restricted to not throw empties real far and the SS109's don't shoot so accurately in it anyhow...just thought it interesting that the RG didn't make enough pressure to run the otherwise reliable rifle.

So..does this say that NATO specs are a maximum...and something can meet the specs yet fall short of the pressure and velocities? If so, then it would seem to indicate that any NATO stamped ammo 'should' be safe to fire, but has no guarantee that it'll run the gun reliably.

 

[Bart B.]

The first problems in big numbers with 30-06 ammo in Garands happened in the mid 1950's when civilians were able to buy them from the DCM. Many used their favorite bolt gun hand loads with slowest powders giving highest muzzle velocity. Many M1's were damaged by high port pressure and the military team support crews had a hard time convincing people that their hand loads produced port pressures at dangerous levels. In spite of claims their hand loads were less than max listed in all reloading data available, many insisted their loads were safe and considered the military armorers incompetent and ignorant, then dashed their Garands again. If the M1's survived the first incident and only needed a new op rod correctly fitted to start with.

Highest port pressure in Garands used by military units was the USAF's long range match load in the 7.62 NATO versions built for them by the USN Small Arms Match Conditioning Unit. A new M118 match primed case with a Sierra 190 atop 44 grains of IMR4320. At about 12,000 to 13,000 psi in the barrel, 'twas a little above the spec for Garands. Exact fitting of op rods let them maintain correct shape and fit. No damage to receivers at all.

http://www.forgottenweapons.com/wp-content/uploads/Garand/Navy Garand 762 Conversion Report.PDF

Note the gas cylinder pressures in the above link's document. They're about 1/5th that of pressure in the barrel at its port.

http://www.m1-garand-rifle.com/gas-pressure.php

 

[jonnyc]

"In todays lawsuit happy environment if there was any significant difference between .308 and 7.62x51 or .223 vs. 5.56 that was a safety issue the lawsuits would be flying. I'm still waiting for verified examples of .223 guns damaged by shooting 5.56 or vice-versa, same for .308 vs 7.62 -- ignoring gas system issues from using inappropriately hot ammo."

Excellent point. And exactly why you will see a number of manufacturers print both ".308" AND "7.62x51" on their boxes. If there was any difference or danger you can be sure they would have all sorts of warnings instead.

 

[Bart B.]

I'm still waiting for verified examples of .223 guns damaged by shooting 5.56 or vice-versa, same for .308 vs 7.62 -- ignoring gas system issues from using inappropriately hot ammo."

I thought I just mentioned some in post 23. Unless there not verified enough.

Those loads damaging Garands were not "hot" if you mean way over spec'd peak pressure. Their pressure curves had normal safe peak pressures but higher average pressures for each mIcrosecond bullets were going past the gas port. Quite a bit more than 10K psi max. Some were estimated to be well over 15K psi.