Question on 7.62 NATO, sold by Winchester

[shotgunjoel]

So I have seen boxes of WWB around labeled as 7.62 NATO. Is this ammo loaded to NATO loadings, or 308 Winchester loadings? I know that someone will say that they are the same cartridge, but they aren't really. They have the same dimensions, but 308 Win is loaded to a higher pressure. I have an older rifle that I'd prefer to shoot the lighter 7.62 ammo in and would like to know if this WWB is actually what it says it is. Thanks.

 

[Davek1977]

Um, why would you believe the ammo is loaded to any other specs than what is on the box? If its loaded to .308 pressures, the box would consider it .308 ammo, not 7.62x51. If its labeled by Winchester as 7.62x51 you can assume its loaded to SAAMI specs for that caliber

 

[USSR]

A couple of things. First, for all intents and purposes, the 7.72x51 and .308 are identical. There are old posts out on the internet that show incorrect pressure spec's for the 7.62x51. The actual difference in pressure spec's is negligible. Secondly, SAAMI only sets spec's for commercial cartridges, and not for military cartridges such as the 7.62x51.

Don

 

[W L Johnson]

They have the same dimensions, but 308 Win is loaded to a higher pressure

You may see 50,000 quoted as 7.62x51's pressure, it is, but in CUP not PSI. People keep changing CUP (Copper Units of Pressure) to PSI without converting. 50,000 CUP = 60,200 PSI. 308 and 7.62x51 were tested using two difference methods thus the two different units. In short, as far as pressure is concerned 308 and 7.62x51(7.62 NATO) are interchangeable.

I have an older rifle that I'd prefer to shoot the lighter 7.62 ammo

There is a slight head space difference between the two which in most rifles is a complete non-issue, but may be an issue in something with borderline head space as in some older mil-surps, so you may want to have your head space checked.

 

[shotgunjoel]

I got my headspace checked on it the other day. Gunsmith said that the headspace was within one or two thousanths of the max. In general, am I correct in assuming that NATO loadings are lighter than 308?

 

[unwise11]

Nato max is 50,000 CUP
.308 is 60,000 usually..
So yes x51 is lighter..

 

[TexasRifleman]

They have the same dimensions, but 308 Win is loaded to a higher pressure.

Nato max is 50,000 CUP
.308 is 60,000 usually..
So yes x51 is lighter..

Oh good grief, this again?

They are NOT the same dimensions and they do NOT have different pressures. They ARE different dimensions slightly which is why headspace issues can cause problems. It's not that the pressure is higher it's that when the pressure is not contained properly really bad things can happen.

If its labeled by Winchester as 7.62x51 you can assume its loaded to SAAMI specs for that caliber

Well no. There are no SAAMI specs for x51.

 

[jonnyc]

No, your assumption is incorrect.
And saying that "308 Win is loaded to a higher pressure" is the same as saying that flag stamps move your mail faster than Elvis stamps.

 

[W L Johnson]

Nato max is 50,000 CUP
.308 is 60,000 usually..
So yes x51 is lighter..

You're confusing two different units, CUP is "Copper Units of Pressure", PSI is "Pounds per Sq Inch". 7.62 NATO was tested in CUP, 308 was tested in PSI.
I'll do the math again
7.62x51 is 50,000 CUP which = 60,200 PSI, which is the same PSI as 308. It's the head-space you have to watch out for. If your head-space is good then the two rounds are interchangeable.

Here a great piece on the issue
http://home.comcast.net/~ehorton/The Truth About 308 Win and 762 NATO.pdf

Even if there was a big pressure difference, 7.62 NATO chambers (per NATO docs) are proofed to 75,000 PSI. So 60,000 PSI is well within pressure specs.

 

[USSR]

They ARE different dimensions slightly which is why headspace issues can cause problems.

Negatory! The ammo dimensions are the same. It is the more "generous" 7.62x51 chamber dimensions that are allowed that can be different and cause short case life when using .308 ammo.

Don

 

[TexasRifleman]

The ammo dimensions are the same. It is the more "generous" 7.62x51 chamber dimensions that are allowed that can be different and cause short case life when using .308 ammo.

Yes and no. The outer dimensions are the same but the case wall is much thicker on x51. So as I said, this is why headspace issues can cause problems since there is a slight difference in the ammo.

That's why people think .308 is "hotter" since it has a tendency to rupture in rifles with headspace at the extreme since the case isn't as strong. x51 can survive without a rupture at a more extreme headspace. Still not a good idea, but the problem just shows up more with .308 leading people to think there is more pressure there.

It's explained very well here:

http://www.303british.com/id36.html

 

[madcratebuilder]

Negatory! The ammo dimensions are the same. It is the more "generous" 7.62x51 chamber dimensions that are allowed that can be different and cause short case life when using .308 ammo.

Don

There are minor differences in their inner case dimensions. NATO brass is thicker and has about 5-% less volume.

Headspace is the difference.

.308 field is 1.6380

7.62 field is 1.6455

Shooting the thinner case .308 in a longer headspace 7.62 chamber may cause case head separations.

This subject has been discussed in length at m14fireingline.

 

[USSR]

There are minor differences in their inner case dimensions. NATO brass is thicker and has about 5-% less volume.

Yes, but headspace dimensions don't come into play when internal case dimensions change. With Nato brass you use less powder to generate the same pressure as the .308. The key facts are: the dimensions and pressure generated by 7.62x51 and .308 are essentially the same. There are no 7.62x51 FL sizing dies.

Don

 

[gwtx]

Hi folks, wow! I am new to reloading and have questions about this topic, but I see that there is apparnently many others who are almost as confused as I am.(almost)
I have read many, many posts and articles, and the confusion goes on and on.
And no wonder, I have commercial .308 cartridges and the bullet is .3075. I have "Winchester 7.62mm" cartridges, and the bullet is .3075 or 7.815mm. I thought 7.62mm(.300), and 30 cal., were supposed to be .300", and/or 7.62mm, or at least really close to that. I see that 7.62x39 bullets actually ARE 7.62mm, so why is American made 7.62x51 cartridges actually 7.82mm?
I look for a starting load using IMR 4064 for my .308, and I see different loads from the same company for the same bullet. I realize there are many variables involved, but it's very confusing for newbies like me. I am very glad there are knowledgeable people willing to share info like you folks. I guess I'll sort throug the available info and then throw out the highs and lows, and take an average

Thanks for a great website.

 

[krinko]

So, Texas Rifleman, I was surprised to see you linking to Steve Redgewell's site, to say the least.
Steve and I had an interesting argument on this subject, years ago-----Short Version---I see these as civilian/military versions of the same caliber, Steve saw them as different calibers.
So I said----"Every time I reload with a different bullet weight, different sizer setting or different powder charge, I'm creating a new caliber?"
Steve said----"Yes."

At which point I had to just walk away.

In retrospect, however, I am proud to have created so many different calibers (all named after me) and will be happy to send a list to anyone who might be using one of my proprietary calibers and who is ready to pay some overdue royalties.
-----krinko

 

[P-32]

GWTX, Don't get confused. The 308 Win has a .308 bullet dia. same as 7.62 nato. Depending on the brass you use, 42.0 grs of IMR 4064 or there abouts with match primers and using a 168 gr. SMK should be pretty close.

 

[W L Johnson]

And no wonder, I have commercial .308 cartridges and the bullet is .3075. I have "Winchester 7.62mm" cartridges, and the bullet is .3075 or 7.815mm. I thought 7.62mm(.300), and 30 cal., were supposed to be .300", and/or 7.62mm, or at least really close to that. I see that 7.62x39 bullets actually ARE 7.62mm, so why is American made 7.62x51 cartridges actually 7.82mm?

Seems to be normal in the gun world. For example, 38 special is not .38 of an inch, it's .357 of an inch. They do the same thing with cars, the 5.0 Mustang was really a 4.9, 5.0 sounded better.

 

[Whiskey11]

They do the same thing with cars, the 5.0 Mustang was really a 4.9, 5.0 sounded better.

Not anymore they don't! The new 5.0 is prim and proper 5.0 L. If they are doing anything with the new 5.0 it's going the other way with the BOSS 302's that are being released, as the new 5.0 is 4.985L or something absurdly close to 5.0 L

As for bullet diameters being larger/smaller than their caliber. It has to do with bullet physics and compression/expansion of bullets when fired. There is a lot of good math behind the bullet diameters and I think it is safe to say, that when buying bullets for reloading, always buy the ones for your caliber as marked on the box, not the diameter!!!

 

[gwtx]

Thanks for the input guys. I'm learning, but it seems to take longer than it used to. I've loaded up some "starting" loads for my .243, .308, and 25-06, but haven't had a chance to shoot'em yet. I tried only neck sizing my .308 brass(fired one time in my rifle) , but it chambered too tight to suit me, so I pulled'em and full length sized'em. They feel better in the chamber now. I have a BLR 81(pre 92), and I have read they have a really tight chamber.
They have a unique bolt, and it doesn't seem to have a lot of leverage when first unchambering a round. Any ideas or wisdom on that rifle??
I don't want to get a case stuck, but I would like to do neck sizing only. I'm loading my own brass, and it is always fired in the same rifle.