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7.62 NATO Vs 308 WIN What's the difference?

13K views 46 replies 31 participants last post by  M14E2 
#1 ·
The following is from 303british.com. I am about to purchase an M1A. I own an HK91 clone and note the rifle can rip the end off the case and in general can't handle 308 WIN.

However, no one seems to mention the M1A having any problems with 308 WIN. Can you use the two rounds interchangably? Accuracy problems? Split cases? etc. Thanks for you insight.





7.62x51mm NATO or 308 Wineschester?
An Armourer Explains the Difference
Do you have a military surplus rifle chambered in 7.62 x 51mm? If so, I'll bet part of the reason you bought it was to get a "308 Winchester" at a really low price. Well, you screwed up. It's like looking at a Northern Pike and a Muskie. They're close yes, but each is distinctive, and you have to understand what you're looking at.



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Early in my military career, I worked on the FNC1 rifle (7.62 NATO). For someone that had previously handled and fired only shotguns and hunting rifles, this was a real treat! Maybe being an armourer wasn't going to be that bad! It was only natural then, that curiousity would generate questions and comparisons about what I thought was the same cartridge - 308 Winchester and the 7.62x51mm NATO.

FNC1

As part of my personal battery, I had a Midland 2100 chambered for 308 Winchester. This rifle was made in England by a small company - Midland Rifle Co I believe - but owned by Parker Hale. Having lots of military 7.62x51mm rounds available, I shot them from my 2100 from time to time. There was never a problem chambering or firing the military stuff. It was a pleasant diversion over the long (read boring) periods spent at the range for base small arms qualifications.
(I traded it off some years ago for a Smith & Wesson Model 686. It's the only rifle I ever regret losing! - Steve)

Around this period I discovered that shooting reloaded cases fired from an FN was virtually impossible. They didn't want to chamber. My frustration led me to ask an older armourer what was wrong. In a nutshell, he told me that they probably didn't fit because they stretched. I was using a Lee Loader in 308 Winchester and didn't know that they only resized the neck, leaving the rest of the case untouched. The shoulders were blown forward on initial firing, so the case was simply too long to fit my rifle's chamber! Hmmm...
I tried the gauges from work in my own rifle. What a shock! None of them would fit! The corporal brought a set in from home and explained the difference. Here's what I discovered.

308 Winchester (SAAMI) Gauges Shop (Military) Gauges
GO - 1.6300" GO - 1.6350"
NOGO - 1.6340" NOGO - 1.6405"
FIELD - 1.6380" FIELD - 1.6455"

The gauge sets were different too! What gives? He told me that the dimensions of the two new and unfired cartridges were basically the same. The difference lay in two areas - chamber size and cartridge makeup.

Chamber Size
Look at the picture below. The top chamber represents a military rifle, the bottom one a commercial sporter. With many military rifles, their chambers can be significantly longer than, say, a Remington 700. Note that the military chamber would fail a NO GO check, but pass a FIELD check using the proper shop (military) gauges.

There is a .013" difference in chamber length however, between these two "Safe & Serviceable" rifles!


The dotted line represents the point on the shoulder where the cartridge would headspace

There will be distinct differences between chambers of military rifles based on:

Type
Ishapur, Garand, FN etc.
Amount of Use
Condition at Time of Sale
Just by looking at the dimensions, you can see that using SAAMI gauges is bound to reveal "problems"

.62x51mm NATO or 308 Winchester? An Armourer Explains the Differences
continued:
Cartridge Makeup
I said at the beginning that these two cartridges were basically the same, dimensionally. While they may share similar external measurements, there is one major difference that you can't see. Case wall thickness.



Military brass is thicker. It needs to be. It was made to function and stretch in a wide variety of firearm chambers. Don't forget that the condition of spent brass is of no importance to the service. Like 99% of military brass, it won't be reused.
Where does that leave you? Follow this rule and you won't have any problems.

DON'T USE YOUR RIFLE IF IT FAILS THE SAAMI FIELD CHECK!!

Why not? Right away you know that the chamber is measuring more than 1.6380" (SAAMI FIELD) - possibly more. It will stretch by a minimum of .008" on first use! Probably more. It may even rupture! You must get the headspace corrected to bring it in line with SAAMI specs. Hey, it's for your own safety! Based on this rule, find your situation below.

I don't reload and use only milsurp ammunition.
You shouldn't have any problems.

I don't reload but want to use commercial ammunition.
There is a potential problem with brass integrity. Commerical cases are NOT as thick as their military cousins. There is less brass, so if you use them in an original, unmeasured military chamber, there may not be sufficient material to stretch and fill the chamber without rupturing. That's bad!!

I reload.
You know that commercial brass is thinner. An easy way to see this is to weigh a fired case of each type. You'll see that the commercial case is lighter. There may not be enough brass left - after lengthening - for any decent case life. You will only aggrevate the situation by full length resizing (it weakens the case by overworking the brass), loading at or near maximum or both.
If you own a milsurp bolt gun like an Ishapore 2A or 2A1, consider neck sizing the brass for better case life, fit and accuracy.

Some Final Thoughts
Military ammunition is loaded to maximum average pressure 50,000 PSI using the modern piezo transducer method of measurement. This standard is used to ensure better consistency round to round. It is proofed at 67,000PSI. The ammunition can then be used in a wide variety of firearms with no ill effects.
Look for the NATO compatibility mark. It indicates that the cartridge is safe to use in any 7.62x51mm NATO firearm in good repair.


NATO mark found on the outside of ammunition containers and the bottom of each case rim.
Commercial ammunition has a SAAMI/ANSI maximum pressure of 62,000PSI. While not every manufacturer may load it to this level, this is the industry established maximum. This is also measured using the piezo transducer method. The proof cartridge pressure is 83,000 to 89,000 PSI. Note the differences between the military test and operational standard vs the commercial one.

The worst case scenario for shooters of 7.62 NATO rifles is as follows. Using a commercially made, maximum pressure cartridge with long headspace, fired from a weak action (ex. converted 93/95 Mausers)! The weaker action is a possible final piece of the 308 vs 7.62 NATO puzzle.
Perhaps no single element will cause your rifle to fail. Maybe you've used your rifle for a while with no ill effects. Usually a rifle will take some abuse before failing. Like a lot of things in life, Murphy's Law - If something can go wrong, it will - could very well catch up with you.
Personally, I don't like the odds.
 
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#2 ·
That is a very long explanation that doesn't really seem to answer the question. I was told that with the 5.56mm versus .223, If you have a Rifle chambered for the Military Spec 5.56mm, you will never have any problem shooting the .223 Rem cartridge. Why? Because the Military chamber is designed to have loose tolerances for dirty ammo in less then ideal shooting environments.

It will accept the tighter tolerance of .223 Rem. HOWEVER, it doesn't work the other way around. Too Tight a chamber to accept the slightly larger/thicker 5.56mm case.

I have no reason to believe that it is any different with the 7.62mm, versus .308 Win.

I'm no armorer, I don't reload, and I only use Military Ball Ammo. So the chance of me ever finding out if this is true is less than a percent.

Just my $.02.
 
#3 ·
Long and detailed description.
Dimensionally the cartridges are the same, the chambers are different.
And they are loaded to different average pressures.

I do question the long held belief that the case walls are of different thicknesses.

I have weighed and measured the internal volume of several brands of commercial as well as military surplus (foreign and domestic) cases. Most of the time the military brass weighed more but also had greater internal volume. This would suggest that it is not brass thickness that accounts for the greater weight but the alloy of the brass.
 
#4 ·
External difference between 7.62mm and 308 Win. are almost identical, internal NATO brass does not have as much volume period. Now back on topic before this gets moved to the reloading or ammo section. USGI chambers are cut long in the throat for a good reason, reliability. Military cases have a thick web to reduce chances for head separation and the brass is very hard compared to commercial cases. Not a whole lot of new rifles are being made with USGI barrels as they are becoming harder to find. Know your rifle and use good old fashioned common sense, no problems.
 
#5 ·
Ok question - is all commercial ammo bad to fire then if your headspace is too long? What about the high quality stuff like Black Hills, Federal, Hornady? How do we know what is "high quality" - do people considered a brand like PMC high quality?
Sorry, this has been confusing me. Thanks!
 
#6 ·
Yute, I have no idea how long the throat is on your rifle. Generally speaking; Federal match brass, as well as Norma, Lapua and I believe a couple others have a thicker web than Winchester or Remington brass, but not as thick as Nato brass. Most of the M14 type rifles in good shape can shoot both 308 commercial & Nato surplus with no problems. If you do have a throat that is longer than Win. 308 no go 1.634 it would be wise to shoot NATO. Even at 1.634+.002 I would think the match ammo would be alright on occasional use. I would stay away from hunting loads if your chamber is that long though. This is what I would feel comfortable doing and is not scientific fact. Try to use good sense and know your rifle.
 
#9 ·
I'll be truthful: I haven't read the above posts as this subject is, IMHO, complete nonsense in the real world.

Surplus 7.62mm NATO is sold daily as ".308 Winchester." This is magically converted by the exotic process of pasting ".308 WIN" labels on the boxes to cover up "7.62mm NATO."

Esoteric minutae aside these cartridges are identical and can be fired by any 7.62mm NATO or .308 Winchester weapon. As can 5.56mm and .223 Remington.

-- Chuck
 
#10 ·
Chuck S said:
I'll be truthful: I haven't read the above posts as this subject is, IMHO, complete nonsense in the real world.

Surplus 7.62mm NATO is sold daily as ".308 Winchester." This is magically converted by the exotic process of pasting ".308 WIN" labels on the boxes to cover up "7.62mm NATO."

Esoteric minutae aside these cartridges are identical and can be fired by any 7.62mm NATO or .308 Winchester weapon. As can 5.56mm and .223 Remington.

-- Chuck

I wholeheartedly DISAGREE with this statement!

This is a free country. You're free to make foolhardy mistakes as long as you are the only one that gets hurt following your own advice!
 
#11 ·
Sherlock308 said:
Chuck S said:
I'll be truthful: I haven't read the above posts as this subject is, IMHO, complete nonsense in the real world.

Surplus 7.62mm NATO is sold daily as ".308 Winchester." This is magically converted by the exotic process of pasting ".308 WIN" labels on the boxes to cover up "7.62mm NATO."

Esoteric minutae aside these cartridges are identical and can be fired by any 7.62mm NATO or .308 Winchester weapon. As can 5.56mm and .223 Remington.

-- Chuck
Sherlock308 wrote;

I wholeheartedly DISAGREE with this statement!

This is a free country. You're free to make foolhardy mistakes as long as you are the only one that gets hurt following your own advice!


+1 here!
 
#12 ·
Maybe this will help put things into perspective. Sorry for the long reply.

Military rifles were designed from the get-go to fire military ammunition and that includes the "aftermarket" military rifles such as the M1a. As a general rule of life, I will not shoot any commercial ammo in my military rifles, nor would I shoot NATO ammo in any commercial rifle, period.

There are three gauges to measure headspace on the M1a/M14: .308 go, .308 no-go, field reject.

I'm under the impression that most M1a/M14 rifles, even new ones, will close on a .308 no-go gauge but not on the field reject gauge which is specifically designed for NATO ammo firing rifles and used by the military to this day. So, while the dimensions between the commercial .308 ammo and the NATO 7.62 x 51 ammo are extremely close, there might be excessive headspace if the rifle closes on the no-go gauge. I'd like someone to verify that.

Having gone through all of this since October when I discovered that my polytech was extremely long it the headspace department, I contacted my armorer and we discussed what to do.

When I had my rifle corrected, I had him install a TRW bolt and still, the headspace was too close for comfort. So, I also had a NM Barrett medium weigh barrel installed. Then, my armorer used an M 852 match reamer to cut the chamber. He did this for me so I COULD shoot commercial ammo as well as NATO ammo in the rifle. I checked with my set of Forster gauges. Sure enough, it would close on the .308 go gauge but not on the .308 no-go gauge. Of course it didn't come close to closing on the field reject gauge.

Some guys can simply swap out the bolts after having them lapped in and restore excessive headspace but it'll still probably close on the 308 no go gauge but be fine for the field reject gauge, makine it perfectly safe for the military ammo but suspect for commercial ammo.

How all of this relates to the ammo, I dont' precisely know, just that there is enough of a difference between the two so that I'd shy away from commercial ammo unless your rifle headspaced correctly on the .308 gauges.

Rome
 
#13 ·
Sherlock308 said:
Chuck S said:
I'll be truthful: I haven't read the above posts as this subject is, IMHO, complete nonsense in the real world.

Surplus 7.62mm NATO is sold daily as ".308 Winchester." This is magically converted by the exotic process of pasting ".308 WIN" labels on the boxes to cover up "7.62mm NATO."

Esoteric minutae aside these cartridges are identical and can be fired by any 7.62mm NATO or .308 Winchester weapon. As can 5.56mm and .223 Remington.

-- Chuck

I wholeheartedly DISAGREE with this statement!

This is a free country. You're free to make foolhardy mistakes as long as you are the only one that gets hurt following your own advice!
Well, he is & he isn't.

My understanding is that if you have a SAMMI spec .308 chamber then you can shoot commercial .308 or milsurp 7.62 ammo. If your chamber is NATO spec (like Cabinetman's Poly) then limit yourself to NATO spec ammo as the commercial ammo may stretch & rupture in the longer chamber (as stated in the article above).

So while there are differences to keep in mind & you should be aware of what they are & what your rifle's headspace is, as far as shooting milsurp NATO 7.62 ammo goes, you should be good to go with a SAMMI or NATO spec chamber. Right or wrong?
 
#15 ·
Polytech marked 308 told it is 7.62NATO ?

My Polytech is marked 308 but I am told by my gunsmith who swapped out the Polybolt bolt for a TRW that he headspaced so that I could shoot 308 but should shoot 7.62 NATO by choice and the Poly is made in 7.62 even though marked 308, is this so. Also do separate makers like LRB and Fulton have different heaadspaces from different makers.
 
#16 ·
I've got the same question as bluedsteelnwood: What does LRB chamber their complete rifles in? I guess I should have asked before I had two on order...

Are there any documented failures of commercial ammo in a NATO spec chamber? Not that it matters, but I find it hard to believe that the commerical ammo is that much worse than some of the milsurp ammo floating around that has passed NATO spec?
 
#17 ·
tbaron55 said:
I've got the same question as bluedsteelnwood: What does LRB chamber their complete rifles in? I guess I should have asked before I had two on order...
I bought an LRB barreled receiver last year (USGI HRA barrel), and it headspaced at the NATO GO spec. Imagine that, a USGI barrel installed on a forged USGI spec M14 receiver headspacing at the NATO GO spec. Who'd of thunk it? 8O :lol:

As most of the barrels they are using these days are non-chrome-lined new commercial production, I'd imagine that they can set the headspace to either spec. If they are smart then they are setting the headspace to ~1.632 like SA does.

Call Lou & ask him.
 
#18 ·
I just spoke to Lou at LRB. He was nice as usual and very helpful. He mentioned that they usually aim for a hybrid headspace at 1.632 but that they can make it what you wish. From what I keep reading all over the place it looks this is the generally accepted headspace to shoot both NATO and civilian ammo...
 
#19 ·
tbaron55 said:
I just spoke to Lou at LRB. He was nice as usual and very helpful. He mentioned that they usually aim for a hybrid headspace at 1.632 but that they can make it what you wish. From what I keep reading all over the place it looks this is the generally accepted headspace to shoot both NATO and civilian ammo...
That's great as long as you have the luxury of having a rifle custom chambered and choose your ammo wisely. The problems begin with off-the-rack rifles with unknown headspace using ammo with an unknown headspace measurement.

Remember that there is chamber headspace and cartridge headspace. Suppose your chamber checks out at 1.632" but you've gotten ahold of some NATO mil-surp ammo where the cases measure 1.638". Or vice-versa. And you aren't aware of it, 'cause you haven't bothered to check it out before firing.

I don't claim to be an expert, and don't have the time or the inclination to quote the textbooks, but if one is really interested in this subject and its ramifications I'd strongly recommend reading p. 117 - p.120 in Scott Duff's book and p.23-24, and p.100 of Jerry Kuhnhausen's book for specific headspace information in relation to the M14 rifle.

Unless you enjoy gambling, like taking unnecessary chances, and don't believe in insurance ;)
 
#20 ·
Sherlock308 said:
tbaron55 said:
I just spoke to Lou at LRB. He was nice as usual and very helpful. He mentioned that they usually aim for a hybrid headspace at 1.632 but that they can make it what you wish. From what I keep reading all over the place it looks this is the generally accepted headspace to shoot both NATO and civilian ammo...
That's great as long as you have the luxury of having a rifle custom chambered and choose your ammo wisely. The problems begin with off-the-rack rifles with unknown headspace using ammo with an unknown headspace measurement.

Remember that there is chamber headspace and cartridge headspace. Suppose your chamber checks out at 1.632" but you've gotten ahold of some NATO mil-surp ammo where the cases measure 1.638". Or vice-versa. And you aren't aware of it, 'cause you haven't bothered to check it out before firing.

I don't claim to be an expert, and don't have the time or the inclination to quote the textbooks, but if one is really interested in this subject and its ramifications I'd strongly recommend reading p. 117 - p.120 in Scott Duff's book and p.23-24, and p.100 of Jerry Kuhnhausen's book for specific headspace information in relation to the M14 rifle.

Unless you enjoy gambling, like taking unnecessary chances, and don't believe in insurance ;)


Excellent advice S308....I believe, (I don't have my Kuhnhausen manual handy now) that he writes that the "average" 7.62 x 51MM cartridge headspace that he has measured was 1.632 so, if you have a chamber of 1.632, your cartridge has no room to expand after detonation.
And, I have personally seen SA Inc. M1A's at gunshows with headspace tags reading as low as 1.631, 1.6315.

There are people who still insist that .308 Winchester cartridge headspace and 7.62x51MM military cartridge headspace are identical. :roll:
 
#21 · (Edited)
There are other factors in the 7.62 NATO and .308 Winchester interchangeability story that are sometimes not examined or considered and to me a design engineer (and a gunsmith) who has been involved in military mil spec engineering and operation all my adult life, very important.

The .308 Win SAMMI Spec and the 7.62x51mm (NATO) MIL SPEC are two different animals and serve two different and separate functions:

The SAMMI spec is an after the fact publication and has not usually been used to design a firearm around in order to take into account the forces present. The SAMMI spec lists a NTE Pressure, a Cartridge OAL, it may list a leade dimension, and it will list chamber dims as well.

The cartridge MIL SPEC is a design spec that lists besides the physical measurement of the empty cartridge brass, and an OAL, it lists all the forces that a engineer must take into account in order to design firearms to operate within the specific forces present in the MIL SPEC: ie specific pressure, a specific projectile, a specific inertia impulse, specific projectile velocity, specific action dwell, specific powder burn rate and gas velocity, and lastly and very important for military firearms, a specific and tested by lot, impact radius for all ammunition loaded to the 7.62 NATO (and US Military) MIL SPEC - the ONLY exception to a measured impact mean is tracer ammunition which gets lighter as the proj proceeds down range. The engineering design overbuild is present in the spec for the individual firearm and is usually 20% of the expected MAX pressure which is also listed in the parent cartridge family spec. This absolute Max pressure is used to develop the "blue pill" test load for a MIL SPEC cartridge.

The chamber dimensions for a MIL Spec cartridge is NOT provided in the cartridge MIL SPEC, it is a separate MIL SPEC that will probably be referenced in the cartridge SPEC. For example the chamber spec for a HKG3 is NOT listed in any of the US MIL SPECS or NATO Cartridge Standardization Agreements (STANAG).

The cartridge MIL SPEC will most likely NOT list head space specs as that is many times specific to a firearm and a firearms family, for example the acceptable head space for an M14 is different to that of an M60, or an M240, or an M1919A4 and is very different from the TIGHT chambers and head space of a turn bolt rifle.

The SAMMI spec lists what the NTE pressure is for the entire family of cartridges, it is not a listing of what the pressure is for each individual manufacturers load is and as a matter of fact we seldom know what the ACTUAL pressure or velocity is of a box we buy off of a retail store shelf OR where it will print on a target at say 600 meters/yards when our military sights are set to 600.
 
#22 ·
Nato 7.62 & .308 SA M1A Standard No Problems

I shoot NATO M80 Ball & the PPU .308 FMJ.

No Problems
 
#24 ·
Nice necro post, noobsauce!

Also excellent first post. Well thought out and interesting. Fleshes out this thread more. There is another that has more info you should do a search if you desire further reading on the subject.

This has been discussed at length many many times.

It keeps going and going and going....


That being said ..


For the purposes of info for new m14 shooters..

They are the same!!!!

But it's interesting to discuss the actual differences.

We all are glad to have you here and i look forward to future posts.
 
#27 ·
Few if any look at the question from a design engineers point of view or from the point of view of one who has had to investigate the failures and why they occur. I am an engineer who has also had to use rifles on the two way range so perhaps I look at things a bit differently, maybe or might work does not cut it.

For all intents and purposes the exterior physical cartridge dimensions are interchangeable - that is a fact. The actual brass construction is not the same, as mil brass is designed to deal with rather energetic extraction (Full Auto) a problem few civilian rifles have a problem with. Running non Mil Spec brass in my M1919A4 results in case head separation after various amounts of time. I would not want to be laying down fire IRL and have malf BECAUSE of the ammo I choose to shoot.

But to say that ALL .308 Win LOADS are interchangeable with ALL 7.62 NATO (Mil Spec) LOADS, which is what one should be considering, is a gross error.

Specific .308 Win Loadings MIGHT be interchangeable with a comparable Mil Spec Load but as an engineer, a weapons design engineer, a machinist, and a gunsmith with 45 years of experience I would look at that on a case by case basis.

I do know that the loaded Mil Spec Cartridge and a SAMMI Spec loaded Cartridge of the same projectile weight will not be EXACTLY the same, they might work in a casual environment. But as a firm believer in Mr Murphy, and in his control of the battle field, an environment where I am trusting my life to it working 100% of the time, there is s reason the cartridges are designed and built to the spec that they are.

Additionally as a combat vet I really like the ammo I choose to use in my firearms to print to the angle of Man ALL THE TIME, when I dial in 600 yards I insist on hitting the man silhouette regardless of what I feed the rifle without checking or adjusting the sights every time I change ammo mfg.
 
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