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Old January 16, 2021, 03:48 PM   #1
TXAZ
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7.62 x 51 is not compatible with .308 ammo?

I was just told the Federal XM80C 7.62x 51 will not work in a .308 rifle at a big box retailer.
I’m pretty sure I’ve fired both “.308” and 7.62x51 out of my .308.
What am I missing? Is this the equivalent of 5.56 vs .223?
I think the clerk is wrong.
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Old January 16, 2021, 03:51 PM   #2
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You should be fine. .308 in a rifle chambered for 7.62x51 might be less safe
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Old January 16, 2021, 04:12 PM   #3
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Thanks Chipperman. That’s what I thought.
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Old January 16, 2021, 05:33 PM   #4
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The external dimensions are identical except for COL, which SAAMI allows to go to 2.810" while the NATO STANAG drawings stop at 2.800" even. Also, the SAAMI case length is 2.015"-0.020", while the military version is 2.015-0.015". The 7.62 NATO chamber has a little more freebore than the SAAMI chamber, so that extra length won't matter to it. The pressure will be lower in the NATO chamber because of the slightly greater room. The SAAMI pressure numbers are 52,000 CUP and 62,000 psi. The military numbers are 50,000 CUP and 60,191 psi (conversion from 4150 Bar). This makes the 308W look like it is a higher pressure cartridge, but you have to bear in mind the military started out with 52,000 CUP but wound up with 50,000 CUP after they had further loosened the chamber for feed reliability

See member FALPhil's article on the subject.
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Old January 16, 2021, 05:43 PM   #5
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Thanks UncleNick.
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Old January 16, 2021, 06:37 PM   #6
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If your rifle has a tight chamber... some surplus ammo might be a tight fit. Extraction wise

As an example South African surplus in a tight Savage chamber.... ( ask me how I know... Lol )
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Old January 16, 2021, 11:07 PM   #7
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TXAZ, I'm fairly certain you might not have one of the Spanish Mausers that were converted to their form of .308 or 7.62. I wish someone else with a better memory than me would come along and give us the low-down on that. But whatever it was, their .308 was loaded down a bit from ours.

I don't recall the basis of that warning, but it gets the blood pressure worked up about the same as the folks who pick sides on the Low Number 1903's. I have seen threads where some folks have shot their .308 Mausers for decades with no blow-ups, blow-aparts, or other issues.

Wait, maybe it was the Spanish CETME? No, I think it was a Mauser.
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Old January 16, 2021, 11:34 PM   #8
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.308 Winchester is the higher pressure on the two. It's the opposite of .223/5.56, where the 5.56 NATO chamber is the higher pressure cartridge.

Last edited by ed308; January 16, 2021 at 11:41 PM.
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Old January 17, 2021, 12:04 AM   #9
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Thanks all for the feedback.
1096 I have a a new Daniel Defense .308.

And from y’all’s feedback, sounds like the clerk was having a bout of Cranial Rectitus.
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Old January 17, 2021, 03:13 PM   #10
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Some info above is totally bogus...they are exactly the same round (your Mother's sister is also called your aunt). There are 2 issues to contend with, however. A commercial .308 chamber is often cut tighter, and a military 7.62 case sometimes has a thicker web and a bit less case capacity.
That's it...two names for the same round.
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Old January 17, 2021, 09:09 PM   #11
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Quote:
Some info above is totally bogus...they are exactly the same round
uuuum.....
No

For most intents and purposes the difference doesn't matter, but they are not the exact same thing
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Old January 17, 2021, 09:42 PM   #12
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A bolt gun is generally stronger than a semi auto. Any military 7.62x51 ammo should be good to go in any 308 bolt gun where it chambers. Most commercial 308 ammo will fire fine in an M1A chambered for 7.62x51 but soft points may hang up during feeding. If in doubt call the manufacturer with the ammo lot number and ask what powder it was loaded with. I bet most are using a powder very close to the original military 7.62x51 ammo because they know a lot will make its way into semi auto rifles.
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Old January 17, 2021, 10:06 PM   #13
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If it were me--I'd call the salesman up and tell him the gun blew up anyway using 308.
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Old January 17, 2021, 10:34 PM   #14
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The issue has more to do with the rifles than the cartridges. Semi, and full auto rifles need the ammo to be loaded to within a fairly narrow pressure range in order to function reliably. Too much pressure, or too little will result in unreliable functioning.

7.62X51 is designed to work in semi-auto rifles. Commercial 308 ammo is generally meant to be used in fixed breach rifles such as bolt, lever or pump actions. Depending on the exact load some commercial 308 may not function reliably in a semi-auto, but even that would be pretty rare.

For all practical purposes 7.62X51 and 308 are the same thing. You will see a wider range of pressure levels in 308 than in 7.62X51, but that isn't specific to 308. You'll see the same thing with every other cartridge. There are very few semi-autos in other cartridges, but you're just as likely to have issues with a semi shooting 243, 30-06, or any other cartridge.

The handful of folks with semi's chambered in those cartridges have to be careful of their ammo choices, and hand loading choices just as much as someone with a semi-auto rifle chambered in 7.62X51.

You're not any more likely to run into a dangerous situation shooting 308 out of a 7.62X51 rifle than you are shooting the wrong ammo out of a 243 or 30-06.
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Old January 18, 2021, 09:18 AM   #15
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Ummm...yeah...other than tolerance differences between different manufacturers...they are.
Show us a difference that is not some internet myth, but is an actual difference worthy of calling them two DIFFERENT cartridges.
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Old January 18, 2021, 10:00 AM   #16
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Quote:
Originally Posted by jonnyc View Post
Ummm...yeah...other than tolerance differences between different manufacturers...they are.
Show us a difference that is not some internet myth, but is an actual difference worthy of calling them two DIFFERENT cartridges.
I think this explains the difference; from post 4:

"See member FALPhil's article on the subject."

It's no different than calling the Caliber 30 M1 military cartridge a 30-06. And the military version listed pressure as 50,000 psi while the commercial version was 60,000 psi and nobody was concerned.

Many thousands of commercial 308 Winchester ammo has been fired in 7.62 NATO semiautomatic service rifles without any problems.

Last edited by Bart B.; January 18, 2021 at 10:28 AM.
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Old January 18, 2021, 10:04 AM   #17
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I’m guessing the guy isn’t familiar with ammo and sees .308 and 6.62x51 listed separately on their inventory list, so they must be incompatible.
So I’m not going to go back and discuss shooting a .38 special out of a .357... or a Taurus Judge
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Old January 18, 2021, 11:30 AM   #18
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So I’m not going to go back and discuss shooting a .38 special out of a .357... or a Taurus Judge
Well dang, you're just being reasonable and no fun at all!
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Old January 19, 2021, 02:27 AM   #19
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We are taking about a big box retailer floor clerk who happens to occupy the square footage around the gun counter.

You might as well get your firearms technical advice from Geraldo Rivera.
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Old January 19, 2021, 11:23 AM   #20
Bart B.
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Originally Posted by Chipperman View Post
You should be fine. .308 in a rifle chambered for 7.62x51 might be less safe
Why might 308's in 7.62 chambers be less safe?

I've shot over a thousand that way.

Last edited by Bart B.; January 19, 2021 at 11:30 AM.
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Old January 19, 2021, 02:50 PM   #21
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Some .308 ammo has a significantly higher pressure than 7.62x51.
If you have a cheap lower quality rifle chambered in 7.62x51 and shoot really hot .308 rounds, it could reach unsafe levels for that rifle.
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Old January 19, 2021, 03:07 PM   #22
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Originally Posted by Chipperman View Post
Some .308 ammo has a significantly higher pressure than 7.62x51.
I'd love to read about that. Can you provide some links?
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Old January 19, 2021, 05:36 PM   #23
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I've been told the reason SOME surplus military ammo is on the market is that it is reject,out of spec ammo.
We bought some Portugese battle pacs of 7.62 NATO that chrono'd quite zippy...around 2900 fps,IIRC.
We had a problem with failure to extract in the Armalite AR-10 T. Brass was left in the chamber. It ran fine in my STG-58 (FN-FAL by Steyr)

The ammo was on the "hot" side. On a global scale " Pull that lot and dispose of it" might mean different things to different people. Some forms of "disposal" are more lucrative than others $$$

Last edited by HiBC; January 20, 2021 at 12:41 AM.
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Old January 19, 2021, 06:36 PM   #24
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I shoot them both in a Savage 99 lever gun. Since I also have a PTR 91, I have accumulated some so-called nato ammo of different makes and marked as such (7.62X51 NATO) ...the 99 never minded it until she read on the internet that she was gonna blow up although I stay away from the tar sealed stuff

I shoot the NATO stuff in the 99 then have some brass to reload...the 99 even has a tight chamber and requires small base dies so it makes it a bit easier when fire-formed....I mostly don't reload the beat up brass from the PTR, even though it is quite feasible to do so.
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Old January 19, 2021, 07:07 PM   #25
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Standard 7..62x51 M80 generates about 50,000 to 52,000 SAAMI CUP depending on which source you look at. (see Unclenick's post above)

My Lyman manual lists multiple .308 loadings >60,000
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