Headspace 7.62 NATO
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Nature Boy
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Same as .308 win
Stevenvalleyky
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I'm sure someone will correct me quickly if I'm wrong but pretty sure I'm not.
Military chambers (both 7.62 and 5.56)are larger chambers than .308 and .223. They also use brass that's a little thicker in the webbing area of the cases. Therefore, you can use military ammo in a commercial 308 and 223 chambers but if you use the thinner commercial brass in the larger, looser military chambers, there is a risk of split cases as the thinner commercial brass stretches to fit the larger chambers. In some cases, it can be done but that's the concern. If you have a gun marked .308 win, you should be able to use both 308 win and 7.62 NATO.
Hope that helps.
Military chambers (both 7.62 and 5.56)are larger chambers than .308 and .223. They also use brass that's a little thicker in the webbing area of the cases. Therefore, you can use military ammo in a commercial 308 and 223 chambers but if you use the thinner commercial brass in the larger, looser military chambers, there is a risk of split cases as the thinner commercial brass stretches to fit the larger chambers. In some cases, it can be done but that's the concern. If you have a gun marked .308 win, you should be able to use both 308 win and 7.62 NATO.
Hope that helps.
looking at the drawings, i cant find any that show a difference between the .308s and x51, chamber or cartridge.
I believe the major issue with shooting .308 commercial ammo in an x51 chamber, is that it generates a few Kpsi more pressure, and is often loaded right up to that limit.
The .223 vs 556 is usually the other way around, .223 spec ammo is considered to be ok in military rifles, but 556 spec ammo Is considered too hot/long/ugly, to shoot in our nice sporting arms.....dont tell my guns that they get fed it all the time.
I believe the major issue with shooting .308 commercial ammo in an x51 chamber, is that it generates a few Kpsi more pressure, and is often loaded right up to that limit.
The .223 vs 556 is usually the other way around, .223 spec ammo is considered to be ok in military rifles, but 556 spec ammo Is considered too hot/long/ugly, to shoot in our nice sporting arms.....dont tell my guns that they get fed it all the time.
Reloadron
Contributing Member
I have a few rifles with barrels marked 7.62 and their chambers are the same dimensions as a .308 Winchester. The two rifles are an old M1A with a match 7.62 barrel and an old match Armalite AR10(T) with a 7.62 barrel. Checking the chamber headspace on both rifles they come in right at 1.631" which is a pretty tight chamber. I checked the chambers using actual chamber headspace gauges. The only way to really accurately check a chamber headspace is using a gauge made for the job Likely the next best method in my humble opinion is to fire a factory round and then measure the case using a good case gauge like the RCBS Precision Mic part #88329. My experience with chambers, based on my own observations is there is no difference between a 7.62 NATO chamber and a .308 Winchester chamber. Here is what I am getting at. The below image is the cartridge (top) and chamber (bottom) for the .308 Winchester.
Here is an example of headspace gauges along with the RCBS Precision Mic.
Something else I have noticed is ammunition including 7.62 NATO surplus stuff I have checked comes in right around 1.630" and normally 1.630" -0.002" and the .308 Winchester cartridge specification calls out 1.634 -0.007 or down to 1.627". Interesting as anything above 1.632" would not chamber in my rifles and I have never run into it. When resizing a case all you want to do is reduce the base to shoulder datum by about 0.002" and there are several gauges available which make this an easy process. You really don't even need to know the chamber actual headspace but it is wise to check a new factory round before firing it and again after firing it. If you start getting cases growing considerably you may want to look at that chamber and see exactly what you have.
Anyway, in conclusion as far as brass and chamber dimensions I am hard pressed to find any difference between the 7.62 NATO and the .308 Winchester cartridges. This past winter I sat down with some GI brass and commercial brass looking at cartridge weight and cartridge volume. The brass used was RP, Win, WCC10, LC 13 and Federal. The results can be seen below as to case weights and volumes. All of the brass was cleaned, sized and trimmed identical. There were 10 pcs of each brass compared.
Take it all for what it's worth.
Ron
Here is an example of headspace gauges along with the RCBS Precision Mic.
Something else I have noticed is ammunition including 7.62 NATO surplus stuff I have checked comes in right around 1.630" and normally 1.630" -0.002" and the .308 Winchester cartridge specification calls out 1.634 -0.007 or down to 1.627". Interesting as anything above 1.632" would not chamber in my rifles and I have never run into it. When resizing a case all you want to do is reduce the base to shoulder datum by about 0.002" and there are several gauges available which make this an easy process. You really don't even need to know the chamber actual headspace but it is wise to check a new factory round before firing it and again after firing it. If you start getting cases growing considerably you may want to look at that chamber and see exactly what you have.
Anyway, in conclusion as far as brass and chamber dimensions I am hard pressed to find any difference between the 7.62 NATO and the .308 Winchester cartridges. This past winter I sat down with some GI brass and commercial brass looking at cartridge weight and cartridge volume. The brass used was RP, Win, WCC10, LC 13 and Federal. The results can be seen below as to case weights and volumes. All of the brass was cleaned, sized and trimmed identical. There were 10 pcs of each brass compared.
Take it all for what it's worth.
Ron
Nature Boy
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I don’t believe that is correct. As Ron noted in his his observations, the difference when comparing the headspace of cases fired in a NATO chamber and a .308 chamber are negligible. I find that to be the case as well.
I also called Springfield Armory about my M1A and asked if commercial .308 would be safe to shoot. Their answer was as long as as it was made to SAAMI spec is was good to go.
Lastly, makers of reloading dies only make .308. I believe it’s their intention that those dies, when set up properly, will resize ammo that will function safely in either chamber
1. SA M1As are designed/chambered to handle either Comm'l 308 -- OR -- Mil 7.62
See page 5: http://www.springfield-armory.com/wp-content/uploads/2014/03/M1AManual.pdf
When reloading, size to the chamber* and/or throw the cases away after a half-dozen full-length sizing cycles.**
2. There is effectively NO pressure difference between Comm'l 308 and Military ball. None.
The "CIP" 62,000 psi cited for NATO rounds is measured at a different location -- AND -- by piezo-electric pressure gauges (true psi, not the old/original copper crusher "CUP" units. Units which are incorrectly cited for the 308Win again and again and again and again... as 50,000 "psi".)
SAAMI 308Win pressure is 63,000 psi
See http://www.saami.org/specifications_and_information/publications/download/206.pdf
* You can custom-size M1A brass/extend its life, but you'better have a Hornady case headspace/comparator gauge set and know what you're doing setting things up. Otherwise, follow rule #1 above. Brass is cheaper than opthamologist visits.
** See http://www.zediker.com/downloads/m14.html
See page 5: http://www.springfield-armory.com/wp-content/uploads/2014/03/M1AManual.pdf
When reloading, size to the chamber* and/or throw the cases away after a half-dozen full-length sizing cycles.**
2. There is effectively NO pressure difference between Comm'l 308 and Military ball. None.
The "CIP" 62,000 psi cited for NATO rounds is measured at a different location -- AND -- by piezo-electric pressure gauges (true psi, not the old/original copper crusher "CUP" units. Units which are incorrectly cited for the 308Win again and again and again and again... as 50,000 "psi".)
SAAMI 308Win pressure is 63,000 psi
See http://www.saami.org/specifications_and_information/publications/download/206.pdf
* You can custom-size M1A brass/extend its life, but you'better have a Hornady case headspace/comparator gauge set and know what you're doing setting things up. Otherwise, follow rule #1 above. Brass is cheaper than opthamologist visits.
** See http://www.zediker.com/downloads/m14.html
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Nature Boy
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......When reloading for the SAI M1A, note that SAI also says doing so will void your lifetime warranty.
The OP didn’t specify what rifle he was shooting but it would be a good guess that it’s an M1A
And of course, they are chambered for both .308/7.62, since It’s a distinction without a difference
To add a visual, attached are cases from the same ammo lot, one fired in a factory .308 chamber, the other in a 7.62 chamber... Pretty dramatic, and worth a thousand words and SAAMI drawings. The photo is from a a Gunsmagazine.com article, and I have experienced similar, to even more dramatic results in my three 7.62x51 chambered rifles.
Edit: Correct source, and add a link.
https://gunsmagazine.com/saami-vs-nato/
Edit: Correct source, and add a link.
https://gunsmagazine.com/saami-vs-nato/
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Does that show a difference in chamber spec or simply different chambers, which may or may not be in spec. Just wondering.
As noted, they only make .308 dies, and it's OK to shoot .308 in a 7.62, assuming, if it is a Garand, the pressure curve is OK.
As noted, they only make .308 dies, and it's OK to shoot .308 in a 7.62, assuming, if it is a Garand, the pressure curve is OK.
Rifle chambers (like people) are all different. If you really want to maximize the fit of your carefully crafted custom ammunition, you really need to make a chamber cast. The cast can be poured or you can do a pound cast. There are many threads in most reloading sites dealing with how to do this. Once you know the exact dimensions of YOUR chamber, you can craft your ammunition accordingly.
Sunray
Member
"...Is that incorrect?..." Yep. Literally millions of rounds of 7.62NATO Ball and commercial .308 hunting ammo have been fired out of both milsurps and commercially hunting rifles with no fuss, for eons. Long before there was an internet to say the 2 cartridges were different.
"...Gunsmagazine.com article..." Usual BS for the gun rags.
"...get a cartridge case headspace gauge..." Waste of money. Cartridges do not have headspace.
"...doing so will void your lifetime warranty..." CYA thing for SA Inc. So does every other manufacturer. Caused by frivolous law suits blaming the manufacturer for the stupidity of some reloaders. Said reloaders who habitually ignore reloading manuals. Mind you, the SA warrantee also says only 7.62NATO ammo is to be used. That means no commercial hunting ammo either.
"...Gunsmagazine.com article..." Usual BS for the gun rags.
"...get a cartridge case headspace gauge..." Waste of money. Cartridges do not have headspace.
"...doing so will void your lifetime warranty..." CYA thing for SA Inc. So does every other manufacturer. Caused by frivolous law suits blaming the manufacturer for the stupidity of some reloaders. Said reloaders who habitually ignore reloading manuals. Mind you, the SA warrantee also says only 7.62NATO ammo is to be used. That means no commercial hunting ammo either.
I'm getting real tired of this statement. It's flat wrong. Period.
Cases DO have a headspace dimension, and it's clearly marked in the SAAMI drawings.
That very real case headspace dimension is also critical to safe reloading and brass life in any M1A.
- Get and Use a Case Headspace Comparator.
- Get and measure five commercial 308 cases and/or commercial cartridges with the Comparator. Write the numbers down
- Fire them in the M1A w/ the gas turned OFF. Measure them again (just for grins).
- Slowly begin to size the five cases (which will lengthen them as the sides are squeezed in) until they won't chamber.
- Then continue sizing reeeeal slowly until they will juuust chamber again with just the barest of feel.
- Measure those cases and take the average. Write it down. That is your absolute MAX case headspace dimension.
- Subtract 0.002"; Write it Down again; and that it your future Size-To dimension for every single session with any brass at any time.
- Do NOT "Set & Forget" the sizing die lock ring. Be prepared to adjust the sizing die each session as brass hardening/springback occurs.
This method works on any chamber of any size in any 308/7.62 that isn't so far out of SAAMI/MilSpec as to be totally ridiculous.
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A set of headspace gauges would tell you if there is something different about your "NATO" chamber. There may be, and there may not be.
A gunsmith bud of mine, he gauged a group of Anniston Arsenal rebuilt M14's for a Army unit. Buds in the unit asked him to check the rifles out before they deployed. He told me every one of those M14's swallowed the civilian field gauge.
If your rifle is a semi auto you cannot tell chamber headspace from the fired cartridges. Gas guns open up when there still is pressure in the chamber, it is called the residual blowback effect, and that stretches the case. These cases were fired out of my Supermatch M1a, had been lubricated and fired lubricated in the rifle. That is why I never got a case head separation in 23 firings. But, if you notice, the shoulder has been moved forward. This is due to the shoulder moving forward as the case was extracted. Because the case was lubricated, none of these cases experienced sidewall stretch, just the shoulder reformed.
But, it you took one of these cases, dropped it in a Wilson gage, you would not be measuring chamber headspace. This is something you can do in bolt action rifles, by the time your finger leaves the trigger, barrel pressure is zero. So cases will fireform to the chamber and show correct bolt face to chamber shoulder distances in a bolt gun.
A gunsmith bud of mine, he gauged a group of Anniston Arsenal rebuilt M14's for a Army unit. Buds in the unit asked him to check the rifles out before they deployed. He told me every one of those M14's swallowed the civilian field gauge.
If your rifle is a semi auto you cannot tell chamber headspace from the fired cartridges. Gas guns open up when there still is pressure in the chamber, it is called the residual blowback effect, and that stretches the case. These cases were fired out of my Supermatch M1a, had been lubricated and fired lubricated in the rifle. That is why I never got a case head separation in 23 firings. But, if you notice, the shoulder has been moved forward. This is due to the shoulder moving forward as the case was extracted. Because the case was lubricated, none of these cases experienced sidewall stretch, just the shoulder reformed.
But, it you took one of these cases, dropped it in a Wilson gage, you would not be measuring chamber headspace. This is something you can do in bolt action rifles, by the time your finger leaves the trigger, barrel pressure is zero. So cases will fireform to the chamber and show correct bolt face to chamber shoulder distances in a bolt gun.
Reloadron
Contributing Member
I do not have a dog in this race. What this stems from is the SAAMI drawing actually and if we go back to post number 6 I posted the SAAMI drawing for the 308 Winchester cartridge and chamber. The chamber is the lower drawing and the cartridge is the upper. The circled X in the lower chamber drawing denotes a headspace dimension. That is called out in the drawing notes on the lower left. The upper cartridge drawing lacks the circle X or any reference to a headspace dimension. Now if we look at the SAAMI Glossary of Terms:
HEADSPACE
The distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats.
HEADSPACE GAGE
A device used in a firearm to determine the distance between the breech face and the chamber surface on which the cartridge seats. Also called Breeching Plug.
The problem starts when a few members like to toss this out, "cases do not have headspace" without any explanation which serves to do nothing more than confuse the new enthusiast. That said if I Google "headspace gauge" I get a hell of a collage from the Hornady Lock-N-Load Headspace Gauge 5 Bushing Set with Comparator to Forster Complete Match Headspace Gauge Set 308 Winchester. Both use the term headspace and obviously they each measure something different. Anyway, we have a few members who like to play that card that "cases do not have headspace" as if their intent is simply to bait the new hand loader with their vast knowledge and fail to explain themselves. The general forum consensus is refer to such as cartridge headspace gauge and be done with it. Playing a game of semantics with a new reloader or hand loader with questions is not a good way to teach.
Ron
.
Huh?
(I think we are in violent agreement -- sorta.
)Your upper drawing actually does emphasize (in red I might add), what we aging deplorables
refer to as case headspace dimension. i.e., the distance from the 0.400" diameter point on the shoulder down to the base of the cartridge: 1.634 - 0.007" or an engineering allowance of between 1.627" to 1.634"It's that case headspace distance/dimension (top pic) that we try to match up as closely to the chamber headspace dimension (bottom pic) as 0.002" clearance will allow to minimize brass stretch.
With that simple understanding, all's well that ends well... and God bless us every one.
Reloadron
Contributing Member
and to all a good night. That was my thinking when I marked up that drawing. I hoped to make the thoughts on the subject simple. Ron
Swampman
Old Fart
The SAAMI "Chart of Unsafe Firearms and Ammunition Combinations" doesn't mention anything about .308 Winchester/7.62x51 NATO.
Since they DO have specific warnings about 5.56x45mm NATO in SAAMI spec .223 weapons and 9x19mm NATO in SAAMI chambered 9mm Lugers, I doubt that it's an oversight.
Chart
Despite the lack of SAAMI warnings, I would still avoid shooting commercial .308 in a converted '93 Mauser, but I honestly don't think full power 7.62x51 NATO would be a great idea either.
Since they DO have specific warnings about 5.56x45mm NATO in SAAMI spec .223 weapons and 9x19mm NATO in SAAMI chambered 9mm Lugers, I doubt that it's an oversight.
Chart
Despite the lack of SAAMI warnings, I would still avoid shooting commercial .308 in a converted '93 Mauser, but I honestly don't think full power 7.62x51 NATO would be a great idea either.
Swampman
Old Fart
At least a 7.62x39 MIGHT fit in a .220 Swift chamber if the bullet got shoved back into the case.
But telling people not to fire .40 S&W in a weapon chambered for 9mm Luger?
But telling people not to fire .40 S&W in a weapon chambered for 9mm Luger?
Stevenvalleyky
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Agreed, kinda dumb. That's like saying "don't fire a 338 Lapua in a 30-06 chamber." That should already be understood.At least a 7.62x39 MIGHT fit in a .220 Swift chamber if the bullet got shoved back into the case.
But telling people not to fire .40 S&W in a weapon chambered for 9mm Luger?
Jim Watson
Member
There is not enough difference, WW to NATO to matter.
I would not shoot any great amount of either in a converted Spanish Mauser.
I note that the STARTING LOADS for .308 are about .300 Savage velocity at or below 7x57 pressure.
That would make a good hunting rifle out of a well done conversion.
I would not use the Chilean conversions with rebored barrel and sleeved chamber for anything.
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