are these to the same as for as firing pressures? if you have a .308 will it safely fire either round and vise versa? im new to the .308 and need help.

7.62x51=.308

.308 is also known as 7.62x51

One in the same.

looky here

No not correct. 308 is hotter than 7.62x51

still not correct



for all intents and purposes new manf weapons will shoot both w/o problems



IB the cup vs psi discussion





 

thats is chocked full of stupid, parts of a discussion that dont have a point



 

ty for the help

Used to be 7.62 was hotter than .308 I wonder what has changed since the late 80's

CUP vs PSI ? yah the two are not the same and can not be interchanged.

FWIW there is also a difference between piezo and strain gauge methods of measuring chamber pressure.

Nope. While you can shoot 308 out of a 7.62 auto loader the same is not true for the reverse . A bolt action chambered for 308 will not properly cycle 7.62x51 in most cases.

Taken from an article on another Forum
Before we go much further, we want to address the oft-posed question “Are the .308 Winchester and 7.62×51 NATO one and the same?” The simple answer is no. There are differences in chamber specs and maximum pressures. The SAMMI/CIP maximum pressure for the .308 Win cartridge is 62,000 psi, while the 7.62×51 max is 50,000 psi. Also, the headspace is slightly different. The .308 Win “Go Gauge” is 1.630″ vs. 1.635″ for the 7.62×51. The .308′s “No-Go” dimension is 1.634″ vs. 1.6405″ for a 7.62×51 “No Go” gauge.

That said, it is normally fine to shoot quality 7.62×51 NATO ammo in a gun chambered for the .308 Winchester (though not all NATO ammo is identical). Clint McKee of Fulton Armory notes: “[N]obody makes 7.62mm (NATO) ammo that isn’t to the .308 ‘headspace’ dimension spec. So 7.62mm ammo fits nicely into .308 chambers, as a rule.” You CAN encounter problems going the other way, however.

.308 hunting ammo will fuck up a Garand or M1A in short order.

I've shot 7.62 out of my 700 with no problems.  I have always read that 308 is hotter than 7.62 like another posted said.

I would think so considering a Garand is .30-06 and neither .308 or 7.62

Untold numbers have been built in both .308 and 7.62. Navy had a bunch of them.

 

that is BS. I know everyone post clint like he is a god but he has never done any testing, just repeats the old TM garbage..
Here is a clip from the FAQ I put together as I dont want to write it out again. As a note there is published worked on other sites where ammo manf have done the CUP test but actually used the piezo strai guage, guess what=same PSI
**As a side note the reason the pressure issue
is confusing is becuase the military measured 7.62 NATO chamber
pressure (PSI) via CUP (in the 40s) vice the normal commercial rating of
PSI  measured (now) with electronic means. You will see many cling to
the 50-55K PSI figure for 7.62 Nato becuase that is what the old Army
TMs have in them. Since there is no conversion for the CUP measurement
to the newer electronic measured PSI, they are two different numbers i.e
no direct comparison. Many people will assume the CUP PSI is the same
as SAAMI/Commercial PSI. It is not.
Commercial PSI is derived from the direct pressure in the chamber
through electronic means (piezo transducer or strain gauges). CUP is a
crush measurement of a copper slug that has been fired, again not the
same test.
The pressure is written as PSI form a cup measurement, while the newer pressures are direct measurments, hence the confusion.





ETA there are two ammo manfs that have done the measurements. If you really want to see the results run a quickload on both, you will be suprised on what you see.



There is other test that have the 7.62 nato at slightly higher pressure than the 308, you can search for them yourself.



This wives tale of pressure differences will not die becuase of stupid people
 

....  This is why I hope you wear eye pro when you shoot.

Also... just look on your barrel.... if it says .308... only shoot specifically bullets that are sold in a .308 box. If it says 7.62x51... then shoot those bullets. Then you have no issues.
I like to call this course of action, " Common Sense"

the bullets are the same diameter





You should really do some reading



 

? I should do some reading because I shoot specifically what my rifle says it is made for? I should do some reading to find out that there are infact differences in a .308 Win and a 7.62x51? namely headspace... also... why do i want to tempt fate by using something other than what is on my barrel... bullet diameters can be the same all day... casings and pressures however... but thank you for looking out for me... i obviously didn't know my head from my asshole.

If you want to go through life ignorant be my guest, you can join the other 99% of the population. If you want to actually understand what something is, rather than just read whats on the box then you will have to sacrifice a little bit of your time.



If you go by what your rifle says, then you would not be able to shoot most of what's on the market.



 

If you want to go through life ignorant be my guest, you can join the other 99% of the population. If you want to actually understand what something is, rather than just read whats on the box then you will have to sacrifice a little bit of your time.



If you go by what your rifle says, then you would not be able to shoot most of what's on the market.



 

controlled pair





 

Jesus H. Christ...

1)  Nobody really has a fucking clue which is "hotter", 7.62x51 NATO or .308.  And I think that in itself says something–– that this debate is a fucking perpetuated internet myth originally caused by ignorance and mixing CUP and PSI and saying "50,000 CUP = 50,000 PSI, so 7.62x51 is lower pressure than .308"  It's bullshit.

What I know is that the 7.62x51 brass is thicker*.  Beyond that there is no practical difference in the ammunition.  Also, military 7.62 chambers are made looser (bigger around) than tight comercial and/or match .308 chambers.  This leads to a theoretically increased possibility of over-stretching a thinner .308 win. case too much in a loose military chamber and rupturing the case or having a case-head separation. I have yet to see a documented case of a properly chambered/headspaced firearm that will reliably safely fire 7.62 Nato, but not .308 winchester.

Likewise I have never seen a case where firing 7.62 Nato ammo out of a .308 has damaged the weapon.  I have shot both out of both thousands of times in multiple weapons and have not experienced a single issue that has made me think "hmm maybe I shouldn't continue doing this".

There is one other issue.  There is a marginally different tolerance for headspace between the two.  There is so much overlap that it's neglegible, and a 7.62 (the "longer" of the two) properly headspaced falls within the "field reject" range of the .308.  They overlap so much it's a moot point.

As with everything firearms related, it is very case-specific.  It may work in one rifle and not the other, it may be safe in one rifle and not another etc.  Try it in your rifle, if you experience pressure issues, stop (There's a concept...).  If not, rock on.  My guess is that 99% of shooters could interchange the two freely without any issues whatsoever.

2) The commercial .308/.30-06 ammunition in M1 Garands and M1a's is an ENTIRELY separate issue.  That has to do with port pressure and is specific to those two rifles.  Slower burning powders that may or may not loaded into commercial ammo have the potential to create port pressures that are too high for the m1/m1a piston system, and can lead to bent operating rods.  Chamber pressure is not related to this in the slightest.



* With the thicker 7.62 Nato brass comes some minor issues with reloading.  Obviously you can't put the same powder charge you would use in a thinner (more internal case capacity) .308 case into a thicker (less internal capacity) 7.62x51 Nato military case and maintain the same pressure.  Pressure will increase.  SOOO, when loading with military brass, drop down to starting loads and work your way up.  This should go without saying when switching any reloading component, but apparently it must be stressed again and again.

It would be "one AND the same" except that they aren't anyway.

Well, there are people that should be hanged that have converted Garands to 7.62x51 and .308.

Either way, it's blasphemy.

You know I usually agree with you, but why are there .308 headspace gauges and specs and 7.62x51 headspace gauges and specs?

My M14S and Ishapore 2A will fail a SAAMI .308 gauge but pass a 7.62x51 gauge.  Both are NATO chambers.

Agreed.  Garand = .30-06 in any normal persons mind

Consider this.  If a military barrel fails a military head space check, the barrel is replaced.

If a used civilian 308 barrel fails a "nogo", it is then checked with a "field reject".  If it passes, it is still safe, if not, gunsmithing is required.

The saami nogo gauge is for brand new guns.  The military nogo is a saami field reject.

basically for reliability, I have all the verbiage in the AR10 FAQ #9



short story, the mil HS is slightly "longer," both will fire fine. You will just get a little more stretch in the mil chambers, externally the cases are basically the same.



 

That is not a result of any dimensional difference between the two calibers, and rather has to do with bullet weight and powder burn rates. I  could easily load a 7.62 NATO round that would damage the operating rod on a Garand or M14, even though they are specifically chambered for that cartridge.

How so on the M14/M1A?  The White Gas system cuts off excess pressure, as per design.

It was a great deal when 7.62x51 was $120/case.  Not so much now.  I did several, with the proper enbloc clips they worked great.

Blasphemer!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

They were generally more accurate, too, for some reason.

I did not know that about the M14. Cool. The statement still applies for the M1, though.

How about an FAL?

i always steer clear of .308 in my FR8s...

nato candy only

The Research has been done.  NATO 7.62 and .308 are the exact same ammo.  Just because one sometimes uses a thicker case does not make it something different.

Guys who think they are the same have both OUTDATED INFO and WRONG INFO.

Mods:  watch the personal attacks comes towards George, and please don't ban me this time because you have some regulars who are tattle tells, and regulars who like to spread wrong info.

Your FR-8's can handle .308 pressures.  Shoot a box through them and look for pressure signs.  You won't find them.  .308's run at the same pressures .30-06 and 8x57mm mauser runs at and the mauser action handles it just fine.  In the looser tolerance military chamber it will generate even less peak pressure.

Because 7.62x51 and .308 are the same!

Seriously, I'd bank on some random country's 7.62x51 NATO ammo to be hot loaded before a commercial and lawsuit liable ammo company...

DS Arms says either 7.62 or .308 is fine in their FAL

I don't know why guys stick to their antiquated and wrong info.  Just because a case might be thicker, and some throats are longer, and they might headspace differently.. does not turn it into something different.  

The way I see .308 and 7.62x51-NATO is the same way I see 32-Fahrenheit and 0-Celsius, both are the exact same with different names.  Now the humidity and barometer levels might vary, but both 32-F and 0-C are the exact same temps!

BTW Mods, please don't ban me.  I always get banned when my info conflicts with one of your "reputable regulars".  Along the way, he will be the one that throws the personal insults, and I get banned because I play along.

WTF are you whining about?



no one had said anything to you, are you on drugs??



 

I am not allowed to whine?  Happens all the time man.  Just letting the mods know up front.  I am learning that being a crybaby has a lot of benefits, such as not getting banned.

So now you calling guys out??? You had differences in the past, but you drag them here, how about just not post.





good luck with that
 

Alright whats the problem here?  I am just letting the mods know up front because I don't want to get in trouble.  I threw no personal insults, but I know it's going to get personal, it always does.  

Also, This does not concern you.  Or does it?  I see you are one of the cool kids around here, I want you to like me, having you like me is my most important task this month.  So what's the issue?  

BTW: Who did I call out, I am just saying this discussion always gets nasty, should that scare me away? Well it does not.  I don't mind the nastiness when it is directed at me.  I am just saying don't ban me for it!

Here is the short Version of a very good article:

"So, to sum everything up, the pressure difference between the 308 Winchester and the 7.62x51mm NATO is less than 2,000 PSI which is statistically  insignificant. The same pressure variation may be achieved by firing any rifle on a hot day and on a cold day or by changing brands of primers. It is safe to  shoot 308 Winchester in your 7.62x51 rifles (even the Ishapores) and vice versa. Handloaders should be aware that they should reduce the amount of powder  when using military 7.62 NATO cases by about 10- 12% and work up to safe pressures with corresponding velocities."


––––––––––––––––––––––––––––––––––––––––––––––––––

Longer Version:


Some fairly current information on this.
Copyright © 2008, Cross Connect Corp. All rights reserved Page 1
The Truth About 7.62x51mm NATO and 308 Winchester
By FALPhil


Introduction

The internet firearms and shooting culture is a relatively close knit group and very computer savvy, as hobby groups go. Many of the community are members of  the several dozen discussion groups that revolve around the special interests of gun owners.  Because of the nature of the internet and the inherent tendency  of human beings towards believing anything that sounds reasonable, without applying critical thinking skills (probably a result of trends in government  school systems – but that is another treatise), there is much misinformation available to the casual gun enthusiast about a variety of subjects concerning  firearms.

One of the most pernicious of these “urban legends” is that there is a significant difference in the pressures between the 7.62x51mm NATO cartridge and the  308 Winchester cartridge. The misinformation indicates that using the commercial offering in a military weapon will visit death and destruction of biblical  proportions upon the miscreant who would attempt such a thing.

I first ran into this ugly rumor in 1996, while participating on the rec.guns usenet forum. It made for interesting reading. At one point, a well-known  Highpower Match competitor, who will remain unnamed, asked the question, “Why would you expect significant differences in pressure when commercial and
military cartridges are loaded with the same technology (powders, primers, cases, and projectiles) and the velocities are very close to each other?” This  issue reared its ugly head a couple of years ago when the many boatloads of Ishapore 2A1 rifles hit the US shores. Much disinformation about what was safe in  these fine rifles was bandied about over the internet.

That got me to thinking. My brother had been a lab technician at Aberdeen Proving Grounds in the late ‘70s, so I called him to ask him about it. It turns out  that he worked on artillery dispersal, but he still knew some technicians involved in small arms research. He said he would reach out to them and get back to
me with some information.

About a month later, my brother called and described to me the method (in general terms) by which small arms ammunition is tested by the US Army. After  speaking to him, I came to my own conclusion that 308 Winchester and 7.62 NATO were completely interchangeable. However, I am an unknown to many firearms  enthusiasts. So, in order to support my position, I have performed a little research and documented my findings.


The Cartridges

The .308 Winchester is a rifle round and is the commercial version of the military 7.62x51mm NATO centerfire cartridge. The .308 Winchester was introduced in  1952, two years prior to the NATO adoption of the 7.62x51mm NATO or T65 round as it was known during testing. Winchester (a subsidiary of Olin Corporation)  branded the cartridge and introduced it to the commercial hunting market as the 308 Winchester. Winchester's Model 70 and Model 88 rifles were subsequently  chambered for the new cartridge. Since then, the .308 Winchester has become one of the most popular short-action big-game hunting cartridges in the world. It  is also commonly used for civilian target shooting, military sniping, and police sharpshooting.

The purpose of the T65 was to achieve the same or similar performance of the then-standard 30-06 cartridge in a package that was more conducive to  reliability in fully automatic weapons and infantry weapons under extreme conditions. A weight savings was a by-product of the project, but it was not a
primary consideration.

While Winchester intended the T65 (later named 7.62x51mm NATO) and 308 Winchester ammunition to be identical and fully interchangeable, there are some  differences. The two primary differences are the specification of chambers size between the two, and the construction or the cartridge case.


Chamber Size

Look at the table below. The right column represents a military headspace gauge specification; the left one, the SAAMI specification. With many military  rifles, the chambers can be significantly longer than say, a Remington 700. Note that the military chamber would fail a NO GO check with a SAAMI gauge, but
pass a FIELD check using the proper military gauges.

There is a .013" difference in acceptability, between these two specifications. This is significant in that, for reloading purposes, brass will stretch more in a military chamber upon firing, thereby reducing the life of the brass and possibly promoting case head separation. But that additional length will allow a round to chamber in an incredibly dirty weapon, which is a requirement for military applications.

308 Winchester (SAAMI) Headspace
GO - 1.6300"
NOGO - 1.6340"
FIELD - 1.6380"

7.62 NATO (Military) Headspace
GO - 1.6350"
NOGO - 1.6405"
FIELD - 1.6455"

However, it must be noted that this is the chamber specification and not the ammunition specification.  The external dimensions of the two types of  ammunition are nearly identical Cartridge Case Construction.

In my personal experiments, I have found, on average, that commercial 308 Winchester cases are able to contain approximately 58 grains of water, on average.  The average for Lake City 92 cases, according to my measurements approached very close to 56.2 grains of water, and for Portuguese NATO markedcases which are  Berdan primed, the average was close to 55.9. All brass had been fired once was sized with the same die, a Hornady New Dimension 308 Winchester die.

These water measurements indicate that, for the military cases, the brass is thicker. This finding was not unanticipated, as the military brass weighs more,  and the military specification calls for the “beefing up” of the area around the web for the purpose of providing an additional safety margin in case the  cartridge is fired in an automatic weapon and the charge is ignited before the cartridge is completely in battery in said weapon.

This characteristic also has implications for hand loaders and other enthusiasts where pressure is concerned. More on that later



Regulating Bodies

The American Sporting Arms and Ammunition Manufacturers' Institute (commonly abbreviated as SAAMI and pronounced "Sammy") is an association of American  firearms and ammunition manufacturers.

SAAMI publishes various industry standards related to the field, including fire code, ammunition and chamber specifications, and acceptable chamber pressure.  SAAMI is an example of industry self regulations.

In the United States firearms and ammunition specifications are not overseen by the Consumer Product Safety Commission or any other branch of government.  Firearms enthusiasts should be aware that only manufacturers that are members of SAAMI are bound by the Institute's guidelines. All other adherence to SAAMI  specifications is strictly voluntary.

The European equivalent of SAAMI is the Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives (Permanent International Commission  for Testing Portable Firearms, commonly abbreviated as C.I.P. or CIP). CIP is funded and mandated by several governments that are part of the
European Union.

There are two other organizations that are germane to this discussion. They are the US Army and the North Atlantic Treaty Organization (NATO). Each has its  own specifications and testing methodologies which are not influenced by commercial interests unless there is a very good reason.


Pressure

Despite working together, the two main industry standards organizations SAAMI and C.I.P. have assigned different standards for some cartridges. This leads to  officially sanctioned conflicting differences between European and American ammunition and chamber dimensions and maximum allowed chamber
pressures.

Under SAAMI proof test procedures, for bottlenecked cases the center of the transducer is located .175" behind the shoulder of the case for large diameter  (.250") transducers and .150" for small diameter (.194") transducers. For straight cases the center of the transducer is located one-half of the transducer
diameter plus .005" behind the base of the seated bullet. Small transducers are used when the case diameter at the point of measurement is less than .35".

Under C.I.P. proof test standards a drilled case is used and the piezo measuring device (transducer) will be positioned at a distance of 25 mm from the  breech face when the length of the cartridge case permits that, including limits. When the length of the cartridge case is to short, pressure measurement  will take place at a cartridge specific defined shorter distance from the breech face depending on the dimensions of the case.  The difference in the  location of the pressure measurement gives different results than the C.I.P. standard.

According to the official C.I.P guidelines the .308 Winchester (referred to as 7.62x51 by CIP) case can handle up to 415 MPa (60,190 psi) piezo pressure. In  C.I.P. regulated countries every rifle cartridge combo has to be proofed at 125% of this maximum C.I.P. pressure to certify for sale to consumers.

The .308 Winchester and 7.62x51mm NATO cartridges are not identical and there are minor differences in their inner case dimensions, though SAAMI does not  list either cartridge as unsafe in a firearm designed for use with the other. [http://www.saami.org/Unsafe_Combinations.cfm].

NATO EPVAT testing is one of the three recognized classes of procedures used in the world to control the safety and quality of firearms ammunition.  EPVAT  Testing is described in unclassified documents by NATO, more precisely by the AC/225 Army Armaments Group (NAAG). EPVAT is an abbreviation for "Electronic  Pressure Velocity and Action Time". This is a comprehensive procedure for testing ammunition using state-of-the-art instruments and computers. The procedure  itself is described in NATO document AC/225 (Com. III/SC.1)D/200.

Unlike the C.I.P. procedures aiming only at the user's safety, the NATO procedures for ammunition testing also includes comprehensive functional quality  testing in relation with the intended use. That is, not only the soldier's safety is looked at, but also his capacity to incapacitate the enemy. As a result,  for every ammunition order by NATO, a complete acceptance approval on both safety and functionality is performed by both NATO and the relevant ammunition  manufacturers in a contradictory fashion. For this, a highly accurate and indisputable protocol has been defined by NATO experts using a system
of reference cartridges.

The civilian organizations C.I.P. and SAAMI use less comprehensive test procedures than NATO, but NATO test centers have the advantage that only a few  chamberings are in military use. The C.I.P. and SAAMI proof houses must be capable of testing hundreds of different chamberings requiring lots of different  test barrels, etc..[7.62 mm. STANAG 2310 and NATO Manual of Proof and Inspection AC/225 (LG/3-SG/1) D/9.]

The US Army continues to use (as of 1995) the M-11 Copper Crusher device for pressure measurements of small arms ammunition. The M-11 was enhanced, when in  1982, it was noted that the results generated at the high end of the test range did not meet NATO standards. [Defense Technical Information Center, ARMY  BALLISTIC RESEARCH LAB/APD, Accession Number : ADP000024]

What is interesting to note is that around the time of the engineering change to the M-11 Copper Crusher device, the US Army changed the units of measurement  for the device from PSI to Copper Units of Pressure, or CUP. Both SAAMI and CIP used the copper crusher method until the advent of inexpensive, reliable  piezoelectric strain gauges, at which point, both organizations converted their methodologies to
take advantage of the newer technology.

The copper crusher method was the standard for small arms pressure measurements since the late 1800s. A copper pellet just like a small watch battery in  placed in the test pressure chamber which is attached to the cartridge chamber, the test round is fired and the copper pellet is then measured with a  micrometer. The micrometer measurement is then converted into a PSI reading by using a chart that converts the length of the pellet into a pressure reading.  The charts are constructed using the theoretical modulus of compression for the particular copper alloy used in the pellet, and may or may not have any  relation to the actual absolute pressure. BUT, the results of the copper crusher method are always relative to previous results, which allows for determining  what is safe and what is not.

Both SAAMI and the CIP have detailed specifications for the arrangement and dimensions of the copper crusher. Because these two systems are not identical,  the two crusher standards cannot always agree.  Further, as explained above, CIP crusher ratings are generally a bit higher than SAAMI's due to differences  in definitions. Also, SAAMI is generally more conservative with older military rounds, such as the 8mm Mauser.

With the SAAMI methodology, the piston is positioned over the brass case, and the case will rupture somewhere below 20,000 PSI. The resulting sudden jump in  pressure under the piston magnifies problems with piston inertia, and this makes the reading more sensitive to parameters such as burning rate, case  strength, and true peak pressure. The CIP methodology requires the piston case be drilled at the sensor location, and the benefit is that crusher and  piezoelectric ratios are much more consistent from cartridge to cartridge, allowing them to reasonably use a conversion formula.



Pressure Confusion

However, neither method addresses the figure “50,000 PSI” that is so often misquoted, especially by “expert” sources such as 6mmbr.com and surplusrifle.com.

This figure comes from the US Army in various technical manuals, most notably, TM-D001-27
Copyright © 2008, Cross Connect Corp. All rights reserved Page 6.  The real problem is the confusion between the old and the new methods of pressure testing.  The old pressure testing method used for the 7.62 NATO cartridge started out life in the 1950s and is still published today in the US Army Technical Manuals.  The figures are based on the copper crusher method in CUP, but are published as PSI.

The new method is the piezoelectric strain gauge transducer method; it is the same technology used today to show an automobile’s oil pressure. The  piezoelectric strain gauge transducer pressure method is a direct pressure reading based on an absolute standard, where the older copper crusher method a  conversion based on a relative measure and a conversion chart. And this is why you see the difference in the pressure readings, but the older 52,000 CUP is  equal to 62,000 PSI (piezoelectric transducer method).

Today, these two methods are called CUP and PSI and the readings are different, but 52,000 CUP equals 62,000 PSI and both are the same pressure, similar to  the way 60 MPH equals 100 KPH.

To add even more confusion about the Ishapore 2A1, which started me on this article, many shooters want to use the headspace specifications set by NATO,  which is different from what the Indian Army set for the Ishapore rifles.

In the figure below, you can actually see a page from an older reloading manual in which equivalent loads are portrayed in both CUP (C) and piezoelectric  transducer PSI (P). Copyright © 2008, Cross Connect Corp. All rights reserved Page 7

Karl Kleimenhagen points out:
In Denton Bramwell's article [http://www.shootingsoftware.com/ftp/psicuparticle2.pdf], a formula is derived using a basic statistical analysis of SAAMI's  ratings, covering only pressures between 28,000 and 54,000 CUP : piezo = 1.52 * crusher - 18

He also demonstrates that within this pressure range, the CIP appears to have generally used a simple conversion between their crusher and piezo ratings,  roughly equal to: piezo = 1.21 * crusher - 2.8
CIP pressures are multiples of 50 bar (about 700 psi), probably rounded after the conversion. (Please note that CIP crusher readings should not be equated  with SAAMI CUP crusher readings.)

In the 09/1968 issue of Handloader, Lloyd Brownell presents test data (crusher, but not necessarily CUP) which suggests a linear conversion formula is not  the best choice, and in my Powley Computer I use:
piezo = crusher * ( 1 + ( crusher^2.2 )/30000 ) From 0 to about 60 ksi crusher, it fits both SAAMI's ratings and Brownell's data well, but it is low at the  high end of Brownell's data. Brownell's data shows little to no error below 20 ksi, and a curve fit to only his data between 20 and 67 ksi crusher is: piezo  = crusher + ( (crusher - 20) ^ 2.3 ) / 210

Conclusions
The pressure difference between the two rounds is insignificant, the real problem is commercial ammunition has thinner cases that were not designed to shoot  in military chambers BUT we do it all the time anyway and this why you see more case head separations on commercial cases fired in military chambers.

The M118 special long range round is loaded to 52,000 CUP (all other U.S. 7.62mm are 50,000 CUP) which would be equal to the pressure levels of commercial  ammunition, this means actually there is no pressure difference between the .308 and 7.62 NATO for the M118 cartridge.

No accurate conversion between copper crusher and true pressure exists, but approximations can be made. In all the conversions outlined above, pressures are  in thousands of PSI (KPSI). Expect errors of several KPSI, or about 15%, with such formulas. Many factors determine how much the indicated pressure reading  from a crusher misses the true pressure, and the error varies among cartridges and even among different loads for one cartridge. The conversions might be  accurate enough for many practical purposes.

So, to sum everything up, the pressure difference between the 308 Winchester and the 7.62x51mm NATO is less than 2,000 PSI which is statistically  insignificant. The same pressure variation may be achieved by firing any rifle on a hot day and on a cold day or by changing brands of primers. It is safe to  shoot 308 Winchester in your 7.62x51 rifles (even the Ishapores) and vice versa. Handloaders should be aware that they should reduce the amount of powder  when using military 7.62 NATO cases by about 10- 12% and work up to safe pressures with corresponding velocities.

References:
[1] ANSI/SAAMI document Z299.4-1992 is the principle source for the SAAMI crusher and piezoelectric
ratings listed here. The ratings listed are the "maximum average pressure". The book they offer is dated
and doesn't include the ratings of newer commercial cartridges. The procedures and definitions should be
current.
[2] The CIP documents are available on their site, and these were the reference for CIP procedures,
definitions, and piezoelectric ratings. In these, past standards for crusher ratings are no longer listed.
Instead, they refer you to past editions when proofing for a cartridge for which no current standard exists.
[3] The Soapbox of Karl W. Kleimenhagen (http://kwk.us/)
[4] Accurate Reloading Guide -
http://www.accuratepowder.com/data/...le/Standarddata(Rifle)/308Cal(7.82mm)/308%
20Winchester%20Pages%20260%20to%20262.pdf

Here Here my man. That is the correct way to settle a dispute, put out the facts and let everone decide for themselves.

Yeah. All that is pretty much the defining characteristics of separate cartridges.

same can be said of any caliber.