.308, 7.62, 7.62 NATO and .223, 5.56 differences R.I.P.

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TNT

New member
I just thought I would post this response from Hornady, I asked them what the differences were from the professionals who would know. Not that I have a .308 but others might. I did know there was a shoulder differences in both. But as in what role it played I was not quite sure. I did allot of reading both in books and internet on this trying to find the right answer so finally I just sent them a email and the next day I got a answer from them. here is what they sent me as a reply. (I did talk to him over the phone as well)

"Tomas, the chambers are different in these firearms. The NATO chambers have much longer throats.
You can fire the 308 Win and 7.62 in a 7.62 NATO chamber but you cannot fire a 7.62 NATO round in a 308 Win chamber.

This is the same for the 223 Rem. verses 5.56.

I tried to call you this morning but you must have been at work. If you have any other questions you are welcome to call me at 1-800-338-3220 so I can explain it better for you.

Thank you"
 
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TNT

New member
This is what they told me I have heard many things but never a definitive answer. I know people have taken the .223 and 5.56 and some have taken the .308 and 7.62 NATO and interchanged them some with no ill effects. And it is entirely possible that this guy may have the right results for the wrong reasons. I just thought I would pass this along. Every rifle is different so it will respond differently as well.
 
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jonnyc

New member
"the chambers are different in these firearms"

If he stopped there he would have been fine. Beyond that he's been reading too much internet myth.
The belief that they're two different rounds might be dead, but he sure didn't kill it.
 
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Art Eatman

Staff in Memoriam
"The NATO chambers have much longer throats." Yup. The leade is longer in the front of the NATO chamber. I don't think I'd use the word "much", however.

it will only make a difference if the NATO bullet protrudes farther from the case neck than the equivalent civilian load and the ogive of the bullet is very close to or touches the entry of the rifling.

It's mainly a potential problem with the .223. I've never seen it matter in the thirty caliber. If you want to shoot 5.56 in a .223 rifle, merely ream a smidgen at the front of the chamber.

In thirteen years at this website and with THR since its inception, I've not read of any eye-witness account of somebody having a problem with shooting a 5.56 round in a .223 chamber.
 
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jukk0u

New member
7.62 military/NATO vs. .308 in the M1A

Springfield claims that only 7.62 NATO/Military ammunition (factory) should be fired in the M1A.
They do not mention head spacing or other issues of measurement but instead refer to the PRIMERS.
They insist that the military primers are harder and resist primer detonation caused by the firing pin which slightly (or more) impacts the primer when the bolt slams forward. (slam fire)

Interestingly the factory manual does not address bullet weight. (which, at heavier weights might affect head space?)
 
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Jim Watson

New member
Agree with Art, the main thing is that military chambers are cut a bit large in one or another dimension because:
1. They will likely be shot hot and dirty.
2. They may be shot with weird ammo from our alleged allies.
3. The Army doesn't reload.

As to primers, I have seen reliable reports of slamfires with unsecured military firing pins.
I wonder how in the world they were able to make Springfields and Garands that would shoot regular .30-06 just fine. (Absent the present worry about somebody loading .30-06 with 4350 or similar and running up the port pressure on an M1.)
 
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blacksky

New member
The Truth About 7.62x51mm NATO and 308 Winchester

Chamber Size:

Look at the table below. The right column represents a military headspace gauge specification; the left one, the SAAMI specification. With many military rifles, the chambers can be significantly longer than, say, a Remington 700. Note that the military chamber would fail a NO GO check with a SAAMI gauge, but pass a FIELD check using the proper military gauges.

There is a .013" difference in acceptability, between these two specifications. This is significant in that, for reloading purposes, brass will stretch more in a military chamber upon firing, thereby reducing the life
of the brass and possibly promoting case head separation. But that additional length will allow a round to chamber in an incredibly dirty weapon, which is a requirement for military applications.

308 Winchester (SAAMI)

Headspace v.s. 7.62 NATO (Military) Headspace

GO 1.6300" v.s. GO 1.6350"
NOGO 1.6340" v.s. NOGO 1.6405"
FIELD 1.6380" v.s. FIELD 1.6455"

Cartridge Case Construction:

Commercial 308 Winchester cases are able to contain approximately 58 grains of water, on average. The average for Lake City 92 cases, according to my measurements approached very close to 56.2 grains of water, and for NATO marked cases which are Berdan primed, the average was close to 55.9. All brass had been fired once was sized with the same die, a Hornady New Dimension 308 Winchester die.

These water measurements indicate that, for the military cases, the brass is thicker. This finding was not unanticipated, as the military brass weighs more, and the military specification calls for the “beefing up” of the area around the web for the purpose of providing an additional safety margin in case the cartridge is fired in an automatic weapon and the charge is ignited before the cartridge is completely in battery in said weapon.
This characteristic also has implications for hand loaders and other enthusiasts where pressure is concerned. :)
 
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Ignition Override

New member
blacksky: Thanks very much. You helped to explain some basics in a nutshell.

Last summer my first Spanish FR8 failed the .308 No-Go gauge, according to the gun smith. He told me that this is often the case in NATO chambers. I ordered a .308 Field Gauge from either Numerich or Brownells, and with this Field the bolt only turns a small bit.

My recent, second FR8 does even better with the field. The bolt will not turn one bit. Both bolts match, learned that a mis-matched bolt can undergo extra stress due to uneven bolt lug contact, even with nice results from a Field gauge.

Hours of research last summer revealed than when military 'cup' adds the normal 10,000 factor
to equal commercial psi,
the max. NATO 7.62 is about 58,000 max. psi, and commercial .308 about 62,000 psi max.
The test pressures are far higher. Correct me where some of this might not be accurate.

Luckily the FR8 is built on the later Spanish 8mm Mauser, which is much stronger than the old (1916) 7mm Spanish Mauser, used for the FR7's action
 
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Jason_G

New member
Springfield claims that only 7.62 NATO/Military ammunition (factory) should be fired in the M1A.
They do not mention head spacing or other issues of measurement but instead refer to the PRIMERS.
Click to expand...

Yeah, but that really doesn't have anything to do with the cartridge dimensions, just differences in primer hardness between NATO ammo and commercial ammo. Sometimes commercial ammo uses soft primers, and the firing pin in an M14/M1A is free floating in the bolt. When the bolt slams home to chamber a round, the pin moves forward due to its own inertia. Usually not an issue, because it's light, and there's usually not enough inertia to cause a significant strike on the primer, and so it doesn't go off. If the primer is really soft, then you could potentially get a slam fire. If you look at a round that has been chambered in your rifle, but not fired, you will notice a shallow dent on the primer from the pin. That's why they throw in the lawyer language CYA statement about the military ammo. NATO ammo typically uses harder primers.

Slam fires aside, your M1A should be headspaced between 1.631" and 1.632", which is the window you want to be in to shoot either 7.62 NATO or .308 Win. A call with SAI will confirm that either should be fine in the rifle. Always keep your rifle pointed downrange, and there's nothing to worry about if using .308. JMHO, YMMV.

Jason
 
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Tim R

New member
Springfield claims that only 7.62 NATO/Military ammunition (factory) should be fired in the M1A.
They do not mention head spacing or other issues of measurement but instead refer to the PRIMERS.
They insist that the military primers are harder and resist primer detonation caused by the firing pin which slightly (or more) impacts the primer when the bolt slams forward. (slam fire)
Click to expand...

Along with the slam fire, the gun still has to have the proper powder burn rate just like the M-1 Garand. Not every 308 out there meets the powder requirements. However

At a military rifle match, we where issued Federal Spun shut ammo to shoot in the match with our tuned M-14's. It came in red boxes with FEDERAL on the box in big whte letters. I always hated that stuff.

The 168 SMK's were spun shut so it could be fired at enemy troops and not be a hollow point. :rolleyes:
 
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Departed402

New member
So if you had to explain .308 and 7.62 NATO interchangeability to a 5-year-old you would say? More specifically, if that 5-year-old was talking about AR-10 type rifles.
 
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jonnyc

New member
First off, I don't know any 5 year-olds with AR-10s, but if I did, I would tell them to read all the posts above. If they're smart enough to handle a full battle rifle, they're smart enough to have understood that there is no difference and the two rounds would be interchangeable in that rifle.
 
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Gunplummer

New member
Bedlamite had a very good post. Go back, pop up the add ons and look close. This argument has been going on for years. There is no simple answer. The answer is always "sometimes". I dealt with these gages for years, and most people using them don't even know what the numbers mean that are on the gage. The military does not even use the same point on the gage to seat against the chamber that SAAMI does. If you take a loaded round that is all the way on the low specs and stick it in a chamber that was cut on the max specs, there could be a serious problem. Add in the European specs and you could get real serious problems. I almost never checked a Mauser that did not fail a SAAMI gage test on the No Go. The previous posts are pretty good. If you can't grasp what is going on with something, get help or don't mess with it.
 
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