.308 Winchester versus 7.62x51 NATO

by Shooting Looney 7. September 2011 01:24

Final Proof: .308 Winchester and 7.62x51 NATO Are The Same On The Outside and completely interchangeable

"But to be safe (as there are other opinions), have your own individual firearm, headspace & ammo checked and approved for use by a qualified gunsmith, BEFORE firing.”


In the 1950s’ the U.S. Government went on a quest to find another newer, better, rifle and cartridge to replace the venerable M1 Garand and the battle proven .30-06 Government.


Previously adopted cartridges, beginning after the Civil War included- but are not limited to- the .50-70- Government, .45-70-405 Government, .30 US Army [otherwise known as the .30-40 Krag], and the .30 US Government 1903, which finally evolved into to the .30 US Government cartridge of 1906, todays’ .30-Ought-Six.


Amongst those cartridges being tested was the .300 Savage, a well-established hunting

round, having been introduced in 1920 and being chambered in many rifles from nearly every American firearm manufacturer, and its’ capabilities were very well known.


The performance of the .300 Savage, in both the lever action Savage Model 99 and the Remington Model 81 Self Loading rifle, was very close to the .30-06 cartridge, and useable on nearly all American Big Game, including Elk. It was loaded with bullets ranging from a 110 gr. at 3080 fps, to a 120 gr. at 2660 fps, and a 180 gr. at a whopping 2370 fps! On average these were only 300 feet per second slower than the .30-06. This is phenomenal when you consider the case was1.871” compared to the 2.494” of the .30-06, with the attendant energies averaging only 200 ft-pounds less.


Without going into too great a history here, it was decided to lengthen the .300 Savage to 2.015”, and reducing the shoulder from 30° to 20°, slightly thinning the cartridge at the base from .4714 to .4703, but keeping the same .473 base, thickening the rim from .049 to .054 and

employing  slightly lesser taper from base to shoulder. As is a popular myth, the .30-06 was not shortened to become the .308 Win/7.62 NATO.


Winchester introduced the .308 cartridge to the sporting world in 1952, and was adopted as the official U.S. Military cartridge in 1954, even though there were, at that time, no suitable military weapon adopted nor chambered for the round. The early military nomenclature was T-65, which was still technically an ‘experimental’ cartridge and rifle, having not yet been adopted.


When the trials finally came to a halt, the .308 Winchester was adopted into the  U.S. Military as the 7.62x51mm, later accepted by NATO, and known as the 7.62x51mm NATO.


The external dimensions of the .308 Winchester and the 7.60x51 NATO cartridge are identical in every way, and completely interchangeable, the differences being the web of the military cartridge is thicker near the base, creating a lower internal capacity, thus necessitating a smaller powder charge to achieve identical ballistics, and a slightly larger chamber dimension, due to the nature of military use; dirt, dust, mud, and sand inevitably being ever-present on the battlefield.


I repeat and stress:



One will find that brass fired in a civilian rifle will easily chamber in a military rifle, while those fired in a military rifle- unless specifically made for competition or sniper use with a tighter competition chamber- will not chamber in the vast majority of civilian rifles, without first full length sizing of the case.


The next question coming into play concerns the 7.62mm CETME cartridge, originally adopted by the  Spanish Military establishment, as compared to the .308W/7.62NATO.


As far as I can find, there is no readily available original, published, statistics as to the internal ballistics of the CETME cartridge, especially wherein it concerns the pressure the cartridge was designed to operate within.


All I have to go on is two pieces of evidence. First is what I myself saw in the late 1970 to mid 1980 timeframe, when many surplus military rifles were being brought into the U.S. by several importers. One such importer, perhaps the most well known, was Century Arms. At that time, one of the rifles they imported was a bolt action Mauser chambered for the 7.62mm CETME, which had a warning tag attached to each rifle that stated to the effect that the .308 Winchester/ 7.62x51 NATO, and the 7.62x51 CETME cartridges were NOT interchangeable in that firearm, and the Winchester/NATO rounds were NOT safe to shoot in them. I was working in a gun store in northern Virginia at the time, and we sold a few.


And second: The original official Spanish CETME rifle was known as the Modelo A, which was chambered for a cartridge known as the 7.9x40mm, a evolutional development of the German 7.92mm Kurz, (7.92x33mm), which shared the StG45 roller-locked, delayed blow back action. The CETME Modelo A was a technical success. However, the non-communist world was then under the influence of the United States Army Ordnance Corps, and was moving towards a uniform adoption of what was to become the 7.62x51mm NATO cartridge.


The Spanish- despite not being members of NATO- saw the what was coming, and brought out the CETME Modelo B. The CETME Modelo B was little more than a product improved Modelo A chambered for A 7.62x51mm cartridge: A 7.62x51mm cartridge because the Modelo B was chambered for two different cartridges! The first of these being the 7.62x51mm CETME, which fired a 112 grain bullet at approximately 2,450 fps, and generated significantly lower chamber pressures, (approximately 42,000 psi, equal to the 7mm Mauser), than the NATO round. The CETME round was a compromise to the Spanish commitment to the intermediate round concept, embodied in the 7.92mm Kurz and the need for interoperability with allied [NATO] forces. 


This is were things get sticky, and confusing. There were literally thousands of model 95~98 Mauser rifles pretty much just lying around, and the Spanish decided to make use of them. It was then that they decided to rebararel the surplus bolt action Mausers to accept the lesser-powered 7.62 CETME cartridge. They were an intermediate/training/fill-in weapon.


And this is where that gets sticky: We don’t know if the actions were made in sabotaged factories near the end of WWII, if the heat treating was correct to begin with, if they were re-heat treated or improperly heat treated, if the barrels were properly heat treated, etc., etc., etc., which is why my advice is to NOT shoot .308/7.62 NATO ammo in any of thie rifles, just to play it safe. As to the  FR-7 and FR-8 question, if it is a small ring Mauser, it will NOT tolerate the 50,000~52,000 psi pressure of the Wunchester/NATO round, and is NOT safe to shoot any ammo over the 7mm Mausers' 42,000 psi pressure range. That means SAFE REDUCED POWER handloads only!


The other cartridge was the standard 7.62mm NATO round, 147 gr. bullet, 2750 +/- 50 fps, and 50,000 psi chamber pressure. By switching the bolt group for one with a different angle on the locking piece cam, and switching springs for a heavier set, the CETME Modelo B could be converted to fire the 7.62mm NATO.


The final iteration of the 7.62mm CETME rifles was the  Modelo C, a copy of the German G3, which was designed to fire only the 7.62mm NATO cartridge, Like all delayed blowback firearms, the chamber is fluted to aid in extraction.The CETME was later produced, under license, by Heckler & Koch as the G3 rifle, and all G3 rifles produced up to 1961 had the word "CETME" stamped into the receiver. The G3 incorporates subtle changes to elements such as the sights, magazine and furniture, but it is functionally identical to the CETME.


I will leave the argument as to which came first- the G3 or the CETME/G3 variation- to others.


Jack R. Looney




Copyright © 2011 Ranging Thoughts. All rights reserved.

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Cartridges | General

Comments (3) -

Las United States
9/26/2011 11:10:31 PM #

A very informative article, thank you. I have 2 comments:
1. When it comes to chamber pressures and safety, nobody seems to address the design safety factor.
As an engineer I typically used a safety factor of 5 when human safety was an issue. That means that for the expected chamber pressure of 42,000 PSI I would have designed it for 210,000 PSI.
So the NATO round has a 52,000 PSI - no problem. Of course, I do not know the actual safety factors used, but why would they use a smaller safety factor than in the civilian designs?
2. Spain did not participate in WW2, so it is doubtful that they were manufacturing their guns in "sabotaged factories".

jackl United States
9/27/2011 1:17:27 PM #

I cannot comment on your #1, since that is WAY over my head, (I am still trying to remember how to use a slide rule for basic math!).
But, as to comment #2:
Spain was at least peripherally involved in WWII, as was the greater parts of Europe, Africa, Asia, etc., but the point of the 'Sabotaged Factories' I refer to was that the German- and German run- factories used what was essentially slave labour nearing the end of the war to produce rifles, handguns, canons, etc.
It is well known that many of those enslaved people used any tactic available to them to make sure the rifles were either off target, (bent barrels were seen in sufficient numbers), shortened firing pins, bad chambers, and, suspect heat treating was at least rumored to have occurred.
Since many of the WWII rifles have been seen all around the world, it is entirely possible that poorly heat treated actions may have made their way into Spain. At the same time, realize that the rifles that were Spanish made were heat treated to withstand the pressures produced by the 7mm Mauser,and there is no proof that the actions were re-heat treated to be capable of handling any other cartridge/pressure safely.
Hence the warning to NOT fire .308 Winchester/7.62 mm NATO ammunition in any rifle not originally designed for that cartridge, or any rifle that has been re-chambered to that cartridge which was not, at the very least, intended for a similar- or greater- pressure producing round.
I have personally witnessed both Model 95 and Small and Large Ring Model 98 actions with the locking lugs set back, creating an unsafe headspace. I remember a gunsmith testing the hardness of several actions and pronouncing them too soft to be safe to shoot. Unfortunately, we have too few qualified gunsmiths available today who are able to make such exams...


stevea United States
12/23/2012 1:06:36 PM #

With the shooting public, in general, being so unaware of the small differences between 7.62x51mm cartridges, I have always wondered why we do not hear of more catastrophic accidents. For instanced in the more than 20 years since we have seen Spanish Mauser Model 1916 and FR7 Mauser being sold as rechambered for 7.62x51mm, there must have been thousands upon thousands of rounds of .308Win. fired through any number of those rifles. Where then is the blood trail/
Steve Ashe

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