7.62x51/.308 out of Springfield M1A?
- Thread starter Smeh
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MIL-DOT
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Yeah, you're fine.
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Z-Michigan
Member
Both are fine.
In .30 caliber, the commercial .308 Win is potentially higher pressure than NATO 7.62x51, however there is also a difference in how the pressure is tested which mutes that difference. In addition they have very slightly different overall dimensions, but nearly all 7.62 ammo will fit within a .308 Win chamber, and most .308 Win chambers are not cut to the SAAMI minimum dimensions that would potentially present an issue.
You are likely to find problems only if you use 7.62 surplus from countries where you wouldn't drink the water (India one good example) or if you have a DPMS .308 which does have a tightly cut chamber in certain of the .308 models (DPMS offers some models that explicitly have 7.62 NATO chamber dimensions instead).
The difference between 7.62 NATO and .308 Win is smaller than the very well known difference between .223 Rem and 5.56 NATO, where you are more likely to have problems or an overpressure situation using 5.56 NATO in a .223 chamber.
In .30 caliber, the commercial .308 Win is potentially higher pressure than NATO 7.62x51, however there is also a difference in how the pressure is tested which mutes that difference. In addition they have very slightly different overall dimensions, but nearly all 7.62 ammo will fit within a .308 Win chamber, and most .308 Win chambers are not cut to the SAAMI minimum dimensions that would potentially present an issue.
You are likely to find problems only if you use 7.62 surplus from countries where you wouldn't drink the water (India one good example) or if you have a DPMS .308 which does have a tightly cut chamber in certain of the .308 models (DPMS offers some models that explicitly have 7.62 NATO chamber dimensions instead).
The difference between 7.62 NATO and .308 Win is smaller than the very well known difference between .223 Rem and 5.56 NATO, where you are more likely to have problems or an overpressure situation using 5.56 NATO in a .223 chamber.
rcmodel
Member in memoriam
Actually, thats not true.
The 7.62 NATO round is loaded to lower pressure (50,000 PSI) then .308 Win commercial (62,000 PSI).
.308 Win:
Minimum Proof Pressure: 83,000 psi
Maximum Proof Pressure: 89,000 psi
7.62 NATO:
Proof pressure: 67,500 psi
The other thing is, Springfield Armory specifically states in the owners manual something to the effect that:
There is also .308 Win "High Performance" ammo that uses slower burning powder to give higher velocity then regular ammo.
That slow powder is not a good match for the gas system of any auto-loader designed for standard burn rate powder.
rc
BaltimoreBoy
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To amplify on what rcmodel said:
I think that the reason the 7.62 is lower pressure is also linked to the 7.62 brass being somewhat thicker. Obviously the kind of powder being used will affect this.
I have read that the reason the 7.62 brass is thicker is because the specification for the 7.62 is 'sloppier' than that for a .308. Because of that a 'large' but still 'in spec' 7.62 chamber might be out of spec (i.e. too large) for a .308. That, combined with the higher pressure could lead to a split case.
All of that said, I have never personally seen anyone with a modern arm run into trouble with the .308. I suppose if you were really worried you could ask a smith to check the 7.62 chamber with a .308 gauge. If you are in spec for .308 I would imagine you'd be good.
This is not gospel - just what I have gleaned from reading several different discussions on this topic.
I think that the reason the 7.62 is lower pressure is also linked to the 7.62 brass being somewhat thicker. Obviously the kind of powder being used will affect this.
I have read that the reason the 7.62 brass is thicker is because the specification for the 7.62 is 'sloppier' than that for a .308. Because of that a 'large' but still 'in spec' 7.62 chamber might be out of spec (i.e. too large) for a .308. That, combined with the higher pressure could lead to a split case.
All of that said, I have never personally seen anyone with a modern arm run into trouble with the .308. I suppose if you were really worried you could ask a smith to check the 7.62 chamber with a .308 gauge. If you are in spec for .308 I would imagine you'd be good.
This is not gospel - just what I have gleaned from reading several different discussions on this topic.
Al Thompson
Moderator Emeritus
It's heavier due to potential full auto fire.
You can certainly over stress a gas operated 7.62 with commercial ammo. It's not the chamber, it's the gas system, especially in an M1A.
The issue with commercial primers is yet another reason to avoid .308 ammo.
Float Pilot
Member
A couple of my older Springfield Armory M1As did not want to chamber civilian 308 ammo. I was trying to shoot some Federal match ammo. Some M1As, particularly the older ones, can be picky about brass head size, and also how deep the bullets are seated.
It seems that military issue ammo is often a touch on the small side, as it also aids in how well it works in full auto applications.
It seems that military issue ammo is often a touch on the small side, as it also aids in how well it works in full auto applications.
W L Johnson
Member
Not this again, the 50,000 rating for 7.62 NATO is not in PSI, it's in C.U.P.. Converted to PSI they're both almost the same PSI and safe to interchange.
I repeat 7.62 NATO is NOT 50,000 PSI it's 50,000 C.U.P. (Which by the way works out to around 60,200 PSI)
P.S. C.U.P. means "Copper units of pressure"
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stubbicatt
Member
The average human hair is 100 microns thick. Thus splitting a human hair would leave to equal pieces of 50 microns apiece. Cite.
When talking of the pressure differential between PSI and CUP and the resulting application to 308 Winchester factory or SAAMI specifications, and the 7.62 NATO specs, you have a negligible, but measurable difference.
Don't split hairs. Shoot the rifle and enjoy it!
When talking of the pressure differential between PSI and CUP and the resulting application to 308 Winchester factory or SAAMI specifications, and the 7.62 NATO specs, you have a negligible, but measurable difference.
Don't split hairs. Shoot the rifle and enjoy it!
W.E.G.
Member
TexasRifleman
Moderator Emeritus
This is correct. 7.62x51 and .308 are the same pressures. One is CUP and one is PSI.
The only difference is some minor chamber dimensions.
The thing to be mindful of is headspace, that's all.
jonnyc
Member
Yes, .308 and 7.62x51 are the same round, however a ".308" chamber is commercial/civilian and will usually be less generous than a military "7.62" chamber.
Springfield recommends military 7.62 due to the design of the firing pin and it's negative effects on commercial primers, as stated above.
Springfield recommends military 7.62 due to the design of the firing pin and it's negative effects on commercial primers, as stated above.
Sunray
Member
"...my M1A can safely fire both 7.62x51 and .308?..." Yes.
"...The M1A is a military weapon..." Nonsense. It's a commercial sporting rifle that is a copy of a military battle rifle.
"...Converted to PSI..." CUP cannot be converted to PSI. Nor can PSI be converted to CUP. CUP is a measurement, not a formula.
"...The M1A is a military weapon..." Nonsense. It's a commercial sporting rifle that is a copy of a military battle rifle.
"...Converted to PSI..." CUP cannot be converted to PSI. Nor can PSI be converted to CUP. CUP is a measurement, not a formula.
W L Johnson
Member
True, there is no conversion per say, for cup is way of testing pressure not an actual unit, so convert may be the wrong word to use. But I'm not sure how else to put it, maybe after the coffee finishes brewing.
I know AR-15's have a floating pin but Armalite AR-10s (7.62 NATO) do have spring on the pin, but mine still sometime leave a tiny mark on the primer even with the spring even with surplus Ammo.
Now were is my coffee Zzzzzzzzzzzzzzzzz
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TexasRifleman
Moderator Emeritus
No but there are correlation tables, so you can get close enough to say that .308 and x51 are about the same.
http://www.shootingsoftware.com/ftp/psicuparticle2.pdf
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