.308 Winchester vs. 7.62x51mm NATO

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Thernlund

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Looked through a few pages of search results with no answer. Soooo....

I know very well that .223 Remington and 5.56x45 NATO aren't completely interchangeable (.223 in a 5.56, but not the other way).

Are the .308 and 7.62x51 interchangeable? More specifically, is anyone using 7.62x51mm NATO rounds in a consumer .308 hunting rifle (like a Ruger M77/MKII)?

I have an M77 (and will have an M1A one day :D) and I'm seeing a bunch of deals on NATO rounds. Ok ya think? Anything I should know about this combination?

Any info is appreciated.


-T.
 
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Unlike as you said about the .223/5.56 the .308 Win/ 7.62X51 have the same pressures and everything else is the same.
 
They're fully interchangeable in either direction...but they're not exactly the same. The true NATO-spec round will provide a little more headspace in a chamber that's cut for the commercial counterpart...and the case itself is sized a tiny bit smaller overall. The reason is feed reliability in automatic weapons under harsh conditions.

Occasionally, you may encounter the odd rifle military in which a commercial round from a given lot won't chamber and go to battery easily.
 
They're fully interchangeable in either direction...but they're not exactly the same. The true NATO-spec round will provide a little more headspace in a chamber that's cut for the commercial counterpart...and the case itself is sized a tiny bit smaller overall. The reason is feed reliability in automatic weapons under harsh conditions.

Occasionally, you may encounter the odd rifle military in which a commercial round from a given lot won't chamber and go to battery easily.
Click to expand...

From what I understood, the external dimensions of .308 and 7.62 NATO cartridges are exactly the same. It's the chamber specifications for the two rounds that *may* be different, because 7.62 NATO has a much looser tolerance for headspace. As such, a tight 7.62 chamber should be identical to a .308 Winchester chamber, and can fire either cartridge without issue. A loose 7.62 chamber, on the other hand, should only be used with 7.62 ammunition, because the 7.62 brass is thicker and safely contains the pressure from firing, even if the headspace of the chamber it's in, is such that the brass isn't fully supported and snug against the chamber wall.

A 7.62 machine gun will likely have a looser chamber, so that it reliably feeds and extracts 7.62 rounds at a high rate of fire and while very hot. But it's not entirely safe to fire .308 rounds out of said machine guns, because of the .308 rounds' thinner brass.
 
I'm still pretty sure that the external dimensional specifications are identical, regardless of how close (or not-so-close) a given ammunition manufacturer gets to those specs...


edit; nevermind, pulled up these dimension specs.

7.62 NATO:
Bullet diameter 7.82 mm (0.308 in)
Neck diameter 8.58 mm (0.338 in)
Shoulder diameter 11.35 mm (0.447 in)
Base diameter 11.84 mm (0.466 in)
Rim diameter 11.94 mm (0.470 in)
Rim thickness 1.27 mm (0.050 in)
Case length 51.05 mm (2.010 in)
Overall length 69.85 mm (2.750 in)

.308 Winchester:
Bullet diameter 0.308 in (7.8 mm)
Neck diameter 0.343 in (8.7 mm)
Shoulder diameter 0.454 in (11.5 mm)
Base diameter 0.470 in (11.9 mm)
Rim diameter 0.473 in (12.0 mm)
Rim thickness 0.050 in (1.3 mm)
Case length 2.015 in (51.2 mm)
Overall length 2.800 in (71.1 mm)
 
If you got those from Wikipedia, be careful about taking that to seriously. There's alot of bickering over there about that stuff. I used to be a part of it and finally gave up.

(I wrote/adapted the ammo sidebar and the conversion code for the inches to mm conversion.)


-T.
 
from this article:

The .308 Winchester and the 7.62mm NATO (nee T-65) cartridges are not the same1, nor should they be considered interchangeable despite apparently identical external dimensions… the chamber drawings are in fact different.

But as Clint McKee and Walter Kuleck of Fulton Armory note on their "award-winning" website:

They are the same, 'cause nobody 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.

.30 calibre rifle chamber graphic, courtesy of Steve Redgwell of http://www.303british.com; used with permission Olin 7.62 X 51mm While the 7.62mm NATO cartridge has a maximum chamber pressure of approximately 50,000 pounds per square inch (psi), in the SAAMI book the .308 Winchester has a MAP (maximum average product) pressure of approximately 62,000 psi* (each by conformal transducer measurements, and therefore comparable). This is not to say that all .308 Winchester loads will develop such pressures, merely that they would be within manufacturing tolerances if they did so. Firing .308 Winchester ammunition in a firearm specifically chambered for the 7.62mm NATO risks damage to the firearm and injury to the shooter.

* - This translates to approximately 52,000 cup (Copper Units of Pressure).
Chamber Headspace Gauges
.308 Winchester
GO: 1.630"
NOGO: 1.634"
FIELD REJECT: 1.638" 7.62 x 51mm NATO
GO: 1.635"

FIELD REJECT: 1.6455"
Chamber Pressures
.308 Winchester
MAP: 62,000 psi
MPSM: 66,000 psi
Minimum Proof Pressure: 83,000 psi
Maximum Proof Pressure: 89,000 psi 7.62 x 51mm NATO
Maximum: 50,000 psi

Proof pressure: 67,500 psi
Sources: .308 Winchester data from ANSI/SAAMI document Z299.4-1992, Pressure and Velocity, Centerfire Rifle Sporting Ammunition

7.62 x 51mm NATO headspace data from Jerry Kuhnhausen's M1/M1A shop manual.

Pressure data from TM 43-001-27: Army Ammunition Data Sheets Small Caliber Ammunition
According to Ken at Clymer Tools, noted maker of headspace gauges, the problem isn't the round itself, it's the headspacing.

A 7.62 NATO Go gauge is .003-inch longer than a .308 Winchester Go gauge. The 7.62 NATO NoGo is also longer, to the tune of .004-inch. It's entirely possible to chamber and have an accident with a .308 Winchester round in a rifle that would be safe for 7.62 X 51mm. A chamber in 7.62 that could barely close on a 7.62 NoGo could swallow a .308 Field gauge. Add to this the fact that .308 Winchester brass, being of commercial manufacture, is much thinner than that of the 7.62 NATO, and expands alot more, could possibly lead to casehead separation.
Click to expand...


There's more in the article, it's an interesting read.


edit; definitely read the article, because the charts don't work well in pure text form. :)
 
Thanks a bunch! :)


-T.


EDIT: Eeek. The article starts out...
At distressingly frequent intervals, someone can always be be counted on to pop up on an Internet Forum somewhere and ask "Is the .308 Win round different than 7.62x51 NATO?".
Click to expand...
I guess that's me. :(
 
Here's another article, from Fulton Armory:


What's the Difference between .308 Winchester & 7.62x51mm NATO?
by Clint McKee and Walt Kuleck
dumb question i alway thought these 2 ammos where interchangeable but some have told me otherwise whats the story??? jim

Hi, Jim,

This is a perennial topic, kinda like ".45 vs. 9mm" or "Best Guns & Loads for Deer."

They are not the same.

They are the same.

They are not the same, 'cause the .308 Win was released by Winchester several years before the Army standarized the T64E3 as the 7.62MM. You'll get an endless discussion of pressure specs, endless because SAAMI and the Ordnance Dep't measured pressure in different, unrelateable ways. Howver, the chamber drawings are different.

They are the same, 'cause nobody (and Clint's been looking for many years!) makes 7.62MM ammo that isn't to the .308 "headspace" dimension spec. So 7.62MM ammo fits nicely into .308 chambers, as a rule.

But in some 7.62MM rifles the chambers are long (to the 7.62MM military spec), notably the Navy Garands with 7.62MM barrels. Thus, using commercial ammo in such a rifle is not a good idea; you need stronger brass. Use military ammo or the best commercial only, e.g., Federal Gold Medal Match.

Most of the time it's a distinction without a difference. But if you intend to shoot .308 commercial in a military arm chambered for 7.62MM, first check the headspace with .308 commercial gauges first. You may get a surprise.

Best regards,

Walt Kuleck
Fulton Armory webmaster
Clint, What's the difference between .308 Winchester & 7.62x51mm NATO?

Jerry Kuhnhausen, in his classic Shop Manual (available from Fulton Armory; see the M1 Rifle Parts & Accessories or M14 Rifle Parts and Accessories Pages under Books) has published a somewhat controversial recommendation concerning .308 Winchester and 7.62x51mm NATO ammo, headspace & chambers. I broached the subject with him some months ago. He had his plate full, so we decided to chat on this in the future. When we do I'll report the results of our conversation.

I completely agree with Jerry that if you have a chamber with headspace much in excess of 1.636 (say, 1.638, SAAMI field reject), you must use only U.S. or NATO Mil Spec Ammo (always marked 7.62mm & with a cross enclosed by a circle) since the NATO mil spec calls for a far more "robust" brass case than often found in commercial (read .308 Winchester) cartridges. It is precisely why Lake City brass is so highly sought. Lake City brass is Nato spec and reloadable (most NATO is not reloadable, rather it is Berdan primed). Indeed, cheaper commercial ammo can fail at the 1.638 headspace (e.g., UMC) in an M14/M1 Garand. Many military gas guns (e.g., M14 Rifles & M60 Machine guns) run wildly long headspace by commercial (SAAMI) standards (U.S. Military field reject limit for the M60 & M14 is 1.6455, nearly 16 thousandths beyond commercial (SAAMI) GO, & nearly 8 thousandths beyond commercial (SAAMI) field reject limit!).

I also agree that 1.631-1.632 is a near perfect headspace for an M14/M1A or M1 Garand chambered in .308 Winchester. But I think that it also near perfect for 7.62mm NATO!

I have measured many, many types/manufacturers of commercial and NATO ammo via cartridge "headspace" gauges as well as "in rifle" checks. If anything, I have found various Nato ammo to be in much tighter headspace/chamber compliance than commercial ammo. Indeed, sometimes commercial ammo can not be chambered "by hand" in an M14/M1A with, say, 1.631 headspace (bolt will not close completely by gentle hand manipulation on a stripped bolt, although it will close & function when chambered by the force of the rifle's loading inertia), though I have never seen this with NATO spec ammo. I.e., if anything, NATO ammo seems to hold at the minimum SAAMI cartridge headspace of 1.629-1.630, better than some commercial ammo!

So, why set a very long 1.636 headspace in an M14/M1A or M1 Garand? It probably is the conflict mentioned above. Military headspace gauges say one thing, SAAMI headspace gauges say something else, as do the spec's/compliance covering ammo. In a court of law, who will prevail? I think Kuhnhausen gave all those who do this work a safe way out. However, I believe it not in your, or your rifle's, best interest. Whether you have a NATO chambered barrel (M14/M1 Garand G.I. ".308 Win."/7.62mm NATO barrels all have NATO chambers), or a .308 Winchester chamber, keep the headspace within SAAMI limits (1.630 GO, 1.634 NO GO, 1.638 FIELD REJECT). This subject is a bit confusing, and for me difficult to explain in a one way conversation!

Clint McKee
Click to expand...


For what it's worth, my Springfield M1A (manufactured in December of '06) has a headspace of 1.632, so I know I'm safe (as long as I stick to 175gr or lighter bullets due to the gas system), whether I load up .308 or 7.62 in my rifle.
 
From a previous post of mine, in regards to the perceived differences in pressure:

MYTH #3 – THE .308 OPERATES AT A MUCH HIGHER PRESSURE THAN 7.62X51, AND THEY ARE DIFFERENT AND SHOULD NOT BE INTERCHANGED.
While there are some articles that are now debunking this, the fact is that guys still continue to post this erroneous info. Now, understand, I am not talking about using just any old .308 ammo in a rifle with port pressure constraints such as the M1 or M14. What I am talking about is the maximum pressure of the two cartridges as determined by the U.S. government (7.62x51) and SAAMI (.308). And therein lies the problem and confusion. While the government lists the 7.62x51 pressure specs as 50,000 psi, it was actually determined using the copper crusher method, and is in fact 50,000 CUP. The government doesn’t subscribe to SAAMI standards, and obviously feels they can call the unit of pressure psi if they want to. The .30-06 is an example of a military cartridge for which we have pressure specs in both CUP and psi: 50,000 CUP and 60,000 psi. If the 7.62x51 was truly 50,000 psi, it would be a cartridge with power similar to the .30-40 Krag, rather than being nearly the ballistic twin of the .30-06. Sometimes you just have to use logic, instead of just accepting information that is obviously flawed.
Click to expand...

The following is from another poster who added additional info:

SAAMI does not list the interchange of 7.62 x 51 and commercial .308 in its list of unsafe combinations of cartridges and chambers, even though 5.56 x 45 is listed as unsafe in a .223 chamber.
http://www.saami.org/Unsafe_Combinations.cfm

People who have actually measured the pressures of both 7.62 and .308 in the same pressure test barrel with the same gauge say that 7.62 may actually be loaded to higher pressure than .308.
http://www.smellysmleshooters.net/ammopressure.htm

If that is not enough, in the Feb. 2008 issue of American Rifleman, the NRA technical editors deal with this exact issue and they say that there is no real pressure difference and that the differences claimed are due to differences in the gauges used (copper crusher vs piezo).

So what is the evidence that .308 is higher pressure than 7.62 and that they were measured by the same gauge?
The evidence is bogus.
Just because the US military lists the specs at 50,000 PSI, you cannot assume that it was measured by the piezo gauge that SAAMI uses for its specs. ALL pressure gauges in the US read in PSI, because that is the standard. In the 1960s, SAAMI and the reloading industry got together and agreed to list PSI values measured by the copper gauge as CUP. The US military standards predate this agreement and the military doesn't care, so they just list the pressure as PSI without indicating that it is a copper crusher measurement.
Click to expand...

Don
 
USSR, do you know what the original government document describing the 7.62x51mm NATO spec is? I've been trying to get my hands on a copy in the interests of being able to point to documented proof showing that the perceived pressure difference stems from different measuring methods. I'm pretty sure this is actually the case, but I'm just going off people's say-so; I'd like to spread the word but don't want to say something unless I know it for a fact.
 
Generally, pressure readings in CUP...Copper Units of Pressure...wil turn up lower numbers than PSI...or Pounds per Square Inch.

i.e. 50,000 CUP usually equates to around 52,500 PSI.

I use the terms "Generally" and "Usually" because CUP readings can vary with the case construction. Wall thickness...Web thickness...Malleabilily of the case material, etc.

It's entirely feasible that a given PSI reading wll produce different CUP readings with a difference in the brass. Thin, soft brass will give a different CUP reading than thick, hard brass,even though the actual pressure in PSI is the same...but assuming that all else is equal...CUP numbers will be a bit lower than PSI.
 
The difference in CUP and piezeo psi is usually more than 5% for high intensity (How many here remember THAT term?) or magnum bottleneck rifle cartridges. I have an IMR pamphlet that shows both. The .270 tops out at 52,000 CUP but the maximum load in the psi section reads 62,000. Be more interesting if they were for the same load, but this is a sign that the two methods diverge a lot.

Note the 50,000 vs 62,000 numbers in the 7.62 vs .308 scare piece; same deal, way more than 5% difference in the methods.


If you think that is tough, try translating British "ton" proof numbers into US practice. Gough Thomas did a piece on that and concluded that like to like, a British proof ton amounted to about 2800 US psi (probably really CUP) at shotgun levels.
 
USSR, do you know what the original government document describing the 7.62x51mm NATO spec is? I've been trying to get my hands on a copy in the interests of being able to point to documented proof showing that the perceived pressure difference stems from different measuring methods. I'm pretty sure this is actually the case, but I'm just going off people's say-so; I'd like to spread the word but don't want to say something unless I know it for a fact.
Click to expand...

The original government document states "50,000psi", but they don't tell you that it was obtained using the copper crusher method. So, you cannot compare it to SAAMI's psi pressure spec's for commercial cartridges which in recent years were obtained using the piezo method, which is what everybody DOES before pronouncing the .308 Winchester producing MUCH higher pressure than the 7.62x51 round. Since we have both CUP and psi pressures for the .30-06 (50K CUP and 60K psi), it is not a stretch to say that the 7.62x51 at 50K CUP would produce nearly 60K psi via the piezo method. And, the difference between a 60K psi 7.62x51 round and a 62K psi .308 round is negligible. Hope that helps.

Don
 
Clear as mud... but, it's straining through the brain filters slowly....

*raises right hand*

I need to use the hall pass...



Actually, this is good educational stuff, although, I have to do some other searches and readings to finally understand some of it... but it's great infromation.
 
I keep posting this and nobody reads it...

http://www.smellysmleshooters.net/ammopressure.htm
Is it safe to shoot 308 Winchester in a rifle chambered for 7.62 NATO?

What about 7.62 in a 308?



By Jim Bullock

I have pressure tested thousands of rounds of ammo in many different calibers both professionally (years ago) and more recently using the facilities of the Canadian Gov't (Explosives Branch) and Expro (maker of IMR powder).

While I don't like sweeping statements, in 308/7.62 I have found that although the specifications have very similar maximum acceptable pressures, the military ammo is usually "hotter".

Commercial ammo tends to run a round 55,000 psi while I have seen some lots of military running around 60,000 psi. (Same pressure gun, observed in the same pressure testing project.)

Ammo specifications can be miss-leading. Military ammo is usually quoted using the CUP system whereas commercial ammo is quoted in psi. The actual pressure maximums are about the same, but the numbers are about 5,000 units apart. This can create the illusion that the military is lower pressure.

The military know what rifles the ammo will be used in and have a guarantee that the rifles will be in good shape. Commercial companies worry about lawsuits. There are rifles in poor condition, miss-matched bolts, unsuitable actions, etc. The last 50 feet per second will cost about 5,000 psi. As a commercial loader I would trade off 50 fps for the safety of 5,000 less pressure, any time. Although commercial ammo can be loaded to 60,000 psi the companies I have discussed this with tell me they don't like to go beyond 57,000 and 55,000 is what they prefer.

The military brass is heavier than commercial brass. I load 308 in commercial brass that weighs 157 grains. I load 7.62 in brass that weighs 195 grains. (I happen to have a large quantity of both types). Since the outside dimensions are the same, we know the internal capacity of the 7.62 case is less because of an extra 38 grains of brass. The powder capacity is very different and the pressure/velocity results of the two are so different I have to treat them as quite different calibers. The light brass can use a larger powder charge and obtain higher velocity at the same peak pressure. The peak pressure of a 308 and a 3006 are the same. The difference is powder capacity. More powder translates to more energy and more velocity. To a lesser extent, the same thing is true of 308 vs. 7.62

Commercial ammo seldom exploits the larger case capacity. In practice I find the military ammo loaded fairly "hot" and commercial ammo is less than max pressure.

Pressure being equal, the military brass offers a significant safety factor. Some actions have chambers with less head support than others, so a thick head is important.

When loading for 303 British the same thing is true about brass weight. Military brass is heavier. Segregate your brass, military vs. commercial and use 2 grains less powder in the military. If you load 3 to 5 grains less than the max powder charge shown in the book you will find the brass lasts much longer. 20 reloads instead of 3 to 5. Just neck size the first quarter inch of the neck, if it is to be shot again in the same rifle.

The suggestion about shooting over a chronograph is an interesting one. If the bullet weight is the same, higher velocity equates to higher pressure, but only if the brass is the same. As I have explained, 308 and 7.62 brass is not the same.

The Hornady Light Magnum ammo I have shot in 308 (both production and experimental) offers significantly higher velocity (around 200 fps) for ordinary pressures (around 55,000 psi). This is accomplished by using a very large charge of compressed slow ball powder. They stuff a 3006 load of slow ball powder into a 308 case. Don't try this at home. You can't do it.

In conclusion, commercial ammo probably has lower pressure than military. Military is safe if the rifle is in good shape. Hornady Light Magnum has unremarkable pressure and I would not hesitate to use it any rifle in good shape.

Handloading and down loading 100 to 200 fps is much easier on the rifle, the brass and the shoulder and is still perfectly fine for punching paper out to 600 yards (about 500 yards farther than is usually required.)



Jim Bullock
Click to expand...
 
One important issue pertaining comercial 308 ammo versus 7.62 Nato ammo is the powder used and the rifle. Specifically the burn rate needs to properly match the intended burn rate in semiauto rifles. Some commercial 308 ammo does not use a powder with the proper burn rate for the M1 Garand or the M14/M1A. I'm very cautious about using commercial ammo in either of these unless I know for a fact they are OK. For my M1 asd M1a I use either military ammo, very carefully handloaded ammo (loaded be me and every piece gauged), or rarely Federal Gold Metal Match. In particular I would be cautious about using 308 hunting ammo in either of these guns as they can run higher pressures and too slow powders.
 
More specifically, is anyone using 7.62x51mm NATO rounds in a consumer .308 hunting rifle (like a Ruger M77/MKII)?
Click to expand...

My understanding is that would be OK. But the reverse is not so.

For example, don't shoot standard pressure commercial .308 in an Ishapore
2a Enfield chambered for 7.62x51mm NATO .
 
My understanding is that would be OK. But the reverse is not so.
For example, don't shoot standard pressure commercial .308 in an Ishapore 2a Enfield chambered for 7.62x51mm NATO .
Click to expand...
You CAN shoot commercial, FACTORY loaded .308 in an Ishapore 2A1 rifle. Commercial .308 is LOWER pressure than military 7.62X51 NATO.
 
so I can't shoot 7.62x51 in my PTR-91? I have heard many people do it and it is advertised as being chambered for .308 caliber.
 
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