7.62x51 Question

[jaytex1969]

Pardon me for a minor thread derail, but I have a relevant ammo question.

I'm a bolt action surplus guy and have several relics requiring 7.62 NATO ammo and not .308. (some may disagree, but that is not the focus of this question)

With these modern AR style weapons, is this still an issue or are they now all cross compatible?


Thanks.

Jay

 

[Robert]

Jay, for all intents and purposes 7.62x51 and 308 are the same cartridge. While there are minor differences in case thickness they are not significant enough to cause issue. Where the controversy came from was the method of measuring pressure in 7.62x51 vs .308.

Modern AR pattern rifles will shot either one just fine.

 

[jmr40]

There are some 308 factory hunting loads, and hand loads that operate at higher pressures, some hand loads at very low pressures. Those work just fine in bolt guns, but may not feed reliably in semi autos of any type. 7.62X51 is going to be loaded to pressure levels that semi-autos are designed to work with. If you have a semi in ANY caliber this is something to be aware of. It isn't dangerous, but lot of the higher pressure ammo could lead to worn parts sooner. In a bolt gun, it is not an issue at all.

 

[Varminterror]

Typically, foreign or surplus 7.62X51 or 308win labeled loads are NATO compliant, sharing the same max allowable pressure as the CIP standards for the 308/7.62 - which are a lower pressure standard than the 308/7.62 SAAMI standard, and measured at a different location in the testing barrel.

So there ARE multiple pressure standards on the market - SAAMI, NATO EPVAT, and CIP for the 308win/7.62x51. But to be clear, both 308win and 7.62x51 are accepted naming and labeling conventions for all of the above compliance standards.

That said - for M1a's, it is typically best to stick to lower pressure NATO/CIP compliant loads. Without doing some gas system tweaking, you'll bend operating rods a lot faster by running SAAMI level loads. AR-10's tend to be a bit more forgiving, but a shooter still needs to match their load level and gas flow to their rifle's action specs, else they'll be tearing up brass and battering their rifle for no good reason. Throttle down the gas and ensure your buffer/carrier weight keeps you locked through the spike long enough to prevent extractor damage and CHS, and you're golden in the AR-10. Really the same in the M1a, just a little more involved to tune.

 

[lobo9er]

still not an issue.

 

[Reloadron]

Winchester White Box does mention 7.62 x 51 and also .308 Winchester on the label. When measuring some actual case dimensions if there is a difference between 7.62 NATO and 308 Winchester I am not seeing it. The Wikipedia, while not all knowing presents it this way: Complete Wiki Link:

Although not identical, the 7.62×51mm NATO and the commercial .308 Winchester cartridges are similar enough that they can be loaded into rifles chambered for the other round, but the Winchester .308 cartridges are typically loaded to higher pressures than 7.62×51mm NATO cartridges.[citation needed] Even though the Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) does not consider it unsafe to fire the commercial round in weapons chambered for the NATO round, there is significant discussion[3][4][5] about compatible chamber and muzzle pressures between the two cartridges based on powder loads and wall thicknesses on the military vs. commercial rounds. While the debate goes both ways, the ATF recommends checking the stamping on the barrel; if one is unsure, one can consult the maker of the firearm.

Winchester White Box Packaging:


That said using Google to find more information you can find just about anything you want from they are the same to if you confuse them your gun will explode and the sky will fall. Really, a simple Google of "308 winchester vs 7.62 nato" or similar will yield dozens of links. In my own observations, firing both from a Remington 700 custom old VSSF over my chronograph there was never any difference to speak of. I have used both in that Remington, my M1A and my AR-10 and never a problem. While I see claims that the 308 Winchester is loaded to higher pressures I never noticed it. As to the actual brass itself? I have seen NATO brass outweigh commercial as well as the other way around. That includes US GI brass. This forum likely has a dozen threads on the subject also so a forum search may get some good dope on the subject.

Ron

 

[carbine85]

I have a DPMS AR10. The ammo isn't a problem either way. .308 or NATO you can shoot what you want.

 

[Bart B.]

If you check SAAMI and MILSPEC data both rounds were developed with in the early 1950's, you'll see the CUP peak average pressures were 50,000 for the military 7.62 ammo and 52,000 for the commercial .308 ammo. Winchester's CUP system had the copper disk at a different location on the chamber than the arsenal's CUP system did.

Arsenal 7.62 ammo fired in Winchester test barrels produced 52,000 CUP so that was the spec Winchester set for their new cartridge called the .308 Winchester.

Arsenal specs for the Garand 30 caliber service and match ammo was also 50,000 CUP.

Read:

https://www.docdroid.net/shd8/the-truth-about-308-win-and-762-nato.pdf.html

 

[FROGO207]

Bart you just have to wonder about all the conflicting info and where it all came from. LOL

 

[stoky]

I've found Winchester White Box to be pretty hot, a couple or three hundred fps faster than surplus DAG.
Some of the conflicting info came from the military. They moved the datum on the 7.62x51 shoulder (at least) twice, trying to wring accuracy out of it for match rifles.
The dimensional differences between .308 and 7.62x51 might not be so trivial, especially in old mil-surp bolt guns with generous head space.

 

[salt&battery]

I had a beautiful Belgian mauser with a peep site where I could not close the bolt on 308 ammo only 7.62x51. I thought it had the metric chamber. I remember US match shooters going to Europe and having trouble with issued metric 308 ammo. that was a while ago maybe straightened out now

 

[Reloadron]

I've Winchester White Box to be pretty hot, a couple or three hundred fps faster than surplus DAG.
Some of the conflicting info came from the military. They moved the datum on the 7.62x51 shoulder (at least) twice, trying to wring accuracy out of it for match rifles.
The dimensional differences between .308 and 7.62x51 might not be so trivial, especially in old mil-surp bolt guns with generous head space.

Have a box of the Winchester White Box sitting here with some numbers. Winchester USA as fired in my M1A ten shot average was 2776 FPS and the same fired in my Remington 700 Bolt gun ran out at 2807 FPS. I have conducted a few science experiments with the M1A turning the gas system on and off and never saw much change in velocities. Those velocities again were Winchester White Box #USA3031 147 grain FMJ bullets. While I do have a few loads which push 150 grain bullets out faster I agree the Winchester White Box at my quoted velocities are moving right along compared to other loads and surplus 7.62 ammunition I have shot.

Ron

 

[Varminterror]

I posted this on another site earlier this year, so I'm copying and pasting the content below:

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

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

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

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


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

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

SAAMI standard for 308 Winchester = 62,000psi


SAAMI standard list - includes 308win on page 43

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

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

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

The important things:

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

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

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

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

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

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

 

[salt&battery]

Have a box of the Winchester White Box sitting here with some numbers. Winchester USA as fired in my M1A ten shot average was 2776 FPS and the same fired in my Remington 700 Bolt gun ran out at 2807 FPS. I have conducted a few science experiments with the M1A turning the gas system on and off and never saw much change in velocities. Those velocities again were Winchester White Box #USA3031 147 grain FMJ bullets. While I do have a few loads which push 150 grain bullets out faster I agree the Winchester White Box at my quoted velocities are moving right along compared to other loads and surplus 7.62 ammunition I have shot.

Ron

I bet you had better groups with the gas shut off on the M1A being no violent movement of the operating rod

 

[Jim Watson]

Looking at the statistics SAAMI uses on ammo, 60190 is not operationally different from 62000.

I think the legend about .308 Win being an overload for 7.62 NATO rifles arose from the Army staying with crusher readings reported as psi - the US Army is not a member of SAAMI or CIP and did not partake of the redefinition to CUP - as the industry moved to transducers which typically give a higher numerical value for the same load. 62000 sounds like a lot more than 50000 if you think they were measured the same way. But they weren't.

 

[Sunray]

7.62 x 51 is the metric designation for .308 Win using the bore diameter and case length. Even though .308" doesn't mathematically convert to 7.62mm. Winchester uses it for marketing purposes.
"...SAAMI standard for 308 Winchester = 62,000psi..." That's the MAX pressure only.
"...the US Army is not a member of..." Not a manufacturer either. SAAMI and CIP are commercial hunting ammo manufacturer's standards so everybody making ammo do so the same way. NATO standard is the US Army's standard.

 

[Reloadron]

I bet you had better groups with the gas shut off on the M1A being no violent movement of the operating rod

Yes, that would be correct. I fired the Winchester White Box (USA) and Federal Gold Medal Match with the gas on and off. What I was looking at is the claim that my case length would change and with gas on or off it didn't change. They went in at 1.630" and came out at 1.635" regardless of the gas being on or off. Yes, with the gas off I can get tighter groups which makes sense to me. I was surprised with gas on or off the ejected cases shared the same case length.

Ron

 

[Bart B.]

In the M14/M1A and M1 gas operated rifles, bullets from them are a few feet past their muzzles before their op rods move from gas pressure.

I knew Springfield Armory used a Fastax camera in the 1950's taking high-speed movies of semiauto rifles timing their functions. Took a while, but I found it. Test bullets' distance from the muzzle when the op rod dwell time (no movement) ended and it started moving back were a bit over 4 feet with the M1; a bit over 6 feet with the M14.

Here's the meat of it......

The unlocking cycle of the M1 Garand and M14 rifles was tested in 1957 by Springfield Armory. The purpose of the test was to determine the average time (in milliseconds) from firing pin contact to:

a. Bullet passing the gas port
b. Bullet exit
c. Initiation of operating rod recoil
d. End of operating rod dwell
e. Completion of bolt unlocking
f. Position of bullet at initiation of operating rod recoil
g. Position of bullet at end of operating rod dwell
h. Position of bullet at completion of bolt unlocking

Three single rounds were fired from each of three M1 and three M14 (T44E4) rifles. The ammunition used was M2 AP for the M1 rifles and armor piercing (T93E1 or T93E2) cartridges for the M14 rifles. Each rifle was fully loaded for each series of three shots. High speed motion picture cameras (operating at 6,000 to 7,000 frames per second; about 1 frame every .015 millisecond) and flash strobes were used to record hammer fall, bullet exit, operating rod movement and bolt unlocking during each firing sequence. Lumiline screens were used to record average bullet velocity at a distance of 53 feet forward of the muzzle. The film was analyzed to obtain the data below. Average values were computed from the high speed film as follows:

Data Item ..........................................................M1 Rifle ..............................M14 Rifle
Type of gas system .............................................gas impingement ...................gas cut-off and expansion
Location of gas port from muzzle ..........................1.5 “ .....................................8.0 “
Gas port diameter ...............................................0.0793 “ ................................0.0768 “
Barrel length ......................................................24 “ ......................................22 “
End of hammer fall ..............................................0 milliseconds ........................0 milliseconds
Bullet passes gas port .......................................1.31 milliseconds ...................1.01 milliseconds
Bullet clears muzzle ...........................................1.36 milliseconds ...................1.25 milliseconds
Initiation of operating rod recoil ...........................1.58 milliseconds ...................1.53 milliseconds
End of operating rod dwell ...................................2.89 milliseconds ..................3.57 milliseconds
Completion of bolt unlocking ...............................4.07 milliseconds ..................5.00 milliseconds
Amount of bullet travel at start of op rod recoil ......7.2 “ past the muzzle .............9.2 “ past the muzzle
Position of bullet at end of op rod dwell .............50.2 “ past the muzzle ..........76.1 “ past the muzzle
Position of bullet at completion of bolt unlocking .....88.9 “ past the muzzle ...........123.0 “ past the muzzle
Average bullet velocity ........................................2735 feet per second .............2733 feet per second

Reference: Springfield Armory Technical Note SA-TN11-1094 dated 16 Dec 1957

 

[Reloadron]

In the M14/M1A and M1 gas operated rifles, bullets from them are a few feet past their muzzles before their op rods move from gas pressure.

On my M1A the gas port is about 7" short of the muzzle. About meaning I used a wood cheap ruler and eyeball to measure.

Interesting in that when I went to quote Bart's post the post reflected considerably more text that what I see above, some really good stuff too. Also interesting and running with Bart's post is I have read claims that the M1A begins ejection before the gas drops. Interesting was not only were the ejected cases the same but there was negligible variance between the muzzle velocities. This would pretty much follow what Bart mentioned in that the bullet is well beyond the muzzle before the operating rod start its movement. All of this of course off topic but interesting stuff.

Ron

 

[Welding Rod]

For a gas operated gun I wonder if the powder burn rate, rather than ultimate pressure level, isn't the most important issue? My M&P10 will short stroke a lot of 762 (but not all), and operates fine on all 308 I have tried except some Blackhills (match I believe) which had pressure signs and blown primers.

 

[Reloadron]

For a gas operated gun I wonder if the powder burn rate, rather than ultimate pressure level, isn't the most important issue? My M&P10 will short stroke a lot of 762 (but not all), and operates fine on all 308 I have tried except some Blackhills (match I believe) which had pressure signs and blown primers.

Reloading for the M14 by Zediker is a good read as to the M1A / M14 loading and powder burn rates. He has a section where he shares his views reading in part:

The M14 has issues with port pressure, and the only issue of influence is knowing the upper limit on burning rate, which is a 4064. I think 4064 is borderline but don’t think it will ever harm a rifle. Others purport to be right in the range but, VARGET®, for instance, is too slow despite what Hodgdon® says. Shoot some and it’s plain. It hurts the rifle. IMR® 4895, Hodgdon® 4895, Accurate Arms® 2495 are, I think, the very best choices. These three are close to the same in burning rates, but I listed them from slowest to fastest. I like Hodgdon® the best and mostly because it meters very well. It also has the more temperature resistant coating akin to VARGET™.

Keeping in mind his focus is the M14 / M1A and not other gas operated rifles in 308 or 7.62 X 51 NATO chambering like the AR-10 or your M&P-10 rifles for example. I have read where the M&P 10 rifles are easily under gassed and many owners have opened the gas port hole but not owning one or having reamed the gas port on one I really can't say that is true with any experience.

Ron

 

[Welding Rod]

With my M&P 10, shooting very sedate reloads using H4895 it operates fine in spite of short stroking much 7.62. Again, why I think powder burn rate must be pretty important.

 

[Llama Bob]

There is not now, and never has been, any difference between .308 and 7.62 NATO. All apparent differences are the result of a) the usual bureaucratic SNAFUs and b) confusion created by copper crush testing mechanisms. If it's factory ammo, interchange them at will. If it's your realoads, as long as you can prove they're within pressure spec it makes no difference. If they're outside pressure spec, you better know what you're doing.

 

[lysanderxiii]

I posted this on another site earlier this year, so I'm copying and pasting the content below:

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

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

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

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


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

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

SAAMI standard for 308 Winchester = 62,000psi


SAAMI standard list - includes 308win on page 43

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

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

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

The important things:

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

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

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

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

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

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

A few things:

1) The pressure you quoted are the maximum agverage plus three sigma pressure level. All have approximately 55,000 psi maximum average.

2) CIP is a commercial entity, much like ISO. Compliance with CIP standards are also voluntary, at least to the extent that those pressure levels are proven safe, and selling stuff over that limit exposes you to legal liability. NATO looks to CIP for the same reason thr DOD looks to ASTM and ANSI, it is cheaper to have someone else maintain the standards, than do it yourself.

3) Military loads are usually near the maximum end of the pressure for the bullet weight, further, if they go over, they can ask for a waiver, and still sell the lot, commercial manufactures have to look at the legal liability aspects if they go over the limits. This makes commercial manufactures design loads to stay comfortably below the Maximum Lot Probable Mean (max + 3 sigma).

4) There are a number of other requirements for military ammunition, that commercial ammuition is not required to meet, such as port pressure, maximum pressure at elevated/depressed temperatures. It is not likely that military spec ammo is made unless under contact. Most of the "military" ammo you see failed some non-safety related requirement, like water-proofing, bullet extraction, or accuracy.

 

[salt&battery]

I have heard for years that the DI system in the AR contributes to accuracy being no operating rod. But Bart B cited the facts. why are bolts more accurate then most gas operated semis then?