.308 Winchester vs. 7.62x51mm NATO

[jonnyc]

I will happily shoot ANY factory .308 in a 7.62 rifle, or ANY factory 7.62 in a .308 rifle. If there were any pressure signs I'd stop. End of story.

Can anyone provide ANY proof of any catastrophic failure due to mixing 7.62x51 and .308??? In my opinion, from everything I've read and believed, they are the same round. The only differences are the chamber tollerances of commercial and military rifles, and the internal capacities of commercial and military cases. Care must be exercised in reloading military cases with heavier loads.

 

[USSR]

The only differences are the chamber tollerances of commercial and military rifles, and the internal capacities of commercial and military cases.

+1. That pretty much sums it up.

Don

 

[Candiru]

Shooting .308 Winchester ammo in a 7.62x51mm rifle is the equivalent of shooting it in a .308 that closes on a NO GO, and possibly closes on a field reject gauge as well. Unfortunately, the allowances between the 7.62x51mm GO and FIELD REJECT are such that a 7.62 chamber could be anywhere between "technically shootable" (longer than .308 NO GO but shorter than .308 FIELD REJECT) and "oh God he's pulling the trigger, everyone take cover" (well beyond .308 FIELD REJECT). This is a chamber tolerance difference, but it's one that introduces safety issues.

Exactly where in this range a particular gun lives is hard to quantify without a full gauge set, so it's usually an uknown. To this, you're adding another unknown: the thickness of your .308 brass. Even name-brand stuff can get pretty thin; just look at the MidwayUSA comments on the large capacity of Winchester .308 cases.

I personally would not shoot .308 Winchester in a 7.62x51mm NATO chamber, and definitely not in an action that starts pulling the brass while there's still pressure in the chamber (any of the delayed blowback systems like the H&K roller lock of FAMAS toggle).

 

[Candiru]

Oh yeah, one more thing...

Does anyone know the name of the military publication citing the approximate 50K "PSI" spec for 7.62x51mm NATO? Even if it doesn't mention the measurement method, I'd like to be able to cite the document instead of saying, "some guy on the internet said so."

 

[USSR]

"1967 National Match Rifles, U.S. Cal. 7.62 M14 and U.S. Cal. .30, M1 and National Match Ammunition", U.S. Army Material Command lists the following:

National Match Ammunition Ballistic Requirements.

7.62mm M118 Velocity 2550 +/- 30 fps.

Pressure - Not to exceed 50,000 lbs./square inch.

Accuracy - 3.50 inch Mean Radius Maximum Average.

Don

 

[Soybomb]

they are the same round. The only differences are the chamber tollerances of commercial and military rifles

So other than being different, they're the same?

Lets look at the numbers:
.308 GO 1.630"
.308 NO-GO 1.634"
7.62 GO 1.6355"
.308 FIELD 1.638"
7.62 NO-GO 1.6405"
7.62 FIELD 1.6455"

So you can have a 7.62 rifle in fine operating condition that will close on a .308 field gauge. Will your thinner commercial brass hold up to excessive headspace that the military brass is made to handle? Probably. Would you risk your face shooting a .308 rifle that closed on a field gauge? Unlikely.

If I had a 7.62 rifle that I wanted to shoot .308 through, I'd put a .308 field gauge in it. If it didn't close, I'd use .308. If it did close I'd try a 7.62 field gauge before shooting it. Ymmv, but I think its a gamble to trust the thinner brass in a gun that would be have excess headspace for the spec of caliber the brass is for.

 

[Candiru]

Thanks, USSR!

Actually, looking at those numbers, 2,550 +/- 30 FPS is pretty slow, even for a 168-grain bullet. Is it possible that those are actual PSI numbers for a downloaded round, or would you have to load even slower to get down to 50K PSI?

 

[USSR]

Actually, looking at those numbers, 2,550 +/- 30 FPS is pretty slow, even for a 168-grain bullet. Is it possible that those are actual PSI numbers for a downloaded round, or would you have to load even slower to get down to 50K PSI?

Candiru,

You have to take into consideration that the velocity numbers are taken at 78 feet by the gov't. This would translate to 2600 - 2630fps at the 10 - 15 foot distance we typically set our chronographs up at (to say nothing of a longer than 22" barrel that may be used). The gov't did their pressure testing with a pressure barrel set up on a M1903 action using the copper crusher method. LC M118 Match ammo is not downloaded, and yes, a 50K psi load would be a weak load.

Don

 

[General Geoff]

So wait, according to Candiru's measurements, my M1A is not within 7.62 spec despite Springfield claiming that all their M1As are... interesting

 

[.45&TKD]

so I can't shoot 7.62x51 in my PTR-91? I have heard many people do it and it is advertised as being chambered for .308 caliber.

Yes, you can. Just don't put commercial .308 in a milsurp chambered for 7.62x51 Nato. A PTR-91 is not a milsurp and is specifically chambered for .308.

 

[1KPerDay]

I'm seeing a bunch of deals on NATO rounds

WHERE??

 

[Thernlund]

http://www.gun-deals.com/

"Deals" is, of course, relative.


-T.

 

[jonnyc]

"So other than being different, they're the same?"

Funny! The rounds are the same. Military chambers are more generous than commercial chambers.

Again, I ask if anyone has any info on catastrophic failure with either factory 7.62 Nato or .308, used in any .308 or 7.62 Nato rifle. I have heard of lots of warnings and rumors, but nothing concrete.

 

[TENmm]

.308 comparison to 7.62mm X 51mm

7.62mm

Type Rifle
Place of origin United States
Service history
In service 1954-present
Used by United States, NATO, others.
Specifications
Parent case .300 Savage
Case type Rimless, Bottleneck
Bullet diameter 7.82 mm (0.308 in)
Neck diameter 8.58 mm (0.338 in)
Shoulder diameter 11.35 mm (0.447 in)
Base diameter 11.84 mm (0.466 in)
Rim diameter 11.94 mm (0.470 in)
Rim thickness 1.27 mm (0.050 in)
Case length 51.05 mm (2.010 in)
Overall length 69.85 mm (2.750 in)
Rifling twist 1:12"
Primer type Large Rifle
Maximum pressure 415 MPa (60,200 psi)
Ballistic performance
Bullet weight/type Velocity Energy
146.6 gr (9.50 g) 2,756 ft/s (840 m/s) 2,472 ft·lbf (3,352 J)



.308 caliber (3 tenths and 8 thousands of an inch)

Type Rifle
Place of origin United States
Production history
Designed 1952
Specifications
Parent case .300 Savage
Case type Rimless, Bottleneck
Bullet diameter 0.308 in (7.8 mm)
Neck diameter 0.343 in (8.7 mm)
Shoulder diameter 0.454 in (11.5 mm)
Base diameter 0.470 in (11.9 mm)
Rim diameter 0.473 in (12.0 mm)
Rim thickness 0.050 in (1.3 mm)
Case length 2.015 in (51.2 mm)
Overall length 2.800 in (71.1 mm)
Rifling twist 1/12
Primer type Large Rifle
Maximum pressure 62,000 psi (430 MPa)
Ballistic performance
Bullet weight/type Velocity Energy
150 gr (9.7 g) Nosler tip 2,820 ft/s (860 m/s) 2,648 ft·lbf (3,590 J)
165 gr (10.7 g) BTSP 2,700 ft/s (820 m/s) 2,671 ft·lbf (3,621 J)
168 gr (10.9 g) BTHP 2,650 ft/s (810 m/s) 2,619 ft·lbf (3,551 J)
175 gr (11.3 g) BTHP 2,600 ft/s (790 m/s) 2,627 ft·lbf (3,562 J)
180 gr (12 g) Nosler partition High-Energy 2,740 ft/s (840 m/s) 3,000 ft·lbf (4,100 J)
Test barrel length: 24 in

these numbers were taken from the following:

http://en.wikipedia.org/wiki/.308_Winchester

http://en.wikipedia.org/wiki/7.62×51_NATO

http://en.wikipedia.org/wiki/7.62_mm_caliber

so no need to think im a genius of gun knowledge

 

[TENmm]

http://www.303british.com/sitebuildercontent/sitebuilderpictures/.pond/rimless2.JPG.w300h266.jpgoh one more linkie http://www.303british.com/id36.html

 

[tribbles]

I think these warnings were written for people who buy surplus 7.62x51 rifles and don't bother to check the headspace. As stated before, the problem comes when you have a loose military chamber on the ragged edge of maximum allowable size, and you chamber a .308 Win cartridge that's been sized for a tight match chamber. Tolerances stack the wrong way, excessive headspace results, and boom.

This is exactly why I set my FAL's headspace to 1.631" when I built it. Well within tolerances for both sets of ammo specs, even after allowing for .001" of locking shoulder setback - no worries.

Now if you want to REALLY get confused, throw the rechambered 1916 Spanish Mauser into the mix.

 

[Art Eatman]

Minor FWIW bits and pieces:

An earlier reference was made to the .30-40 Krag. It's only loaded to 40,000 psi because of the single-lug bolt. Same deal for US-made 7x57 Mauser commercial ammo.

I've run across Argentine 7.62 which doesn't seem to be much over maybe 45,000 psi, just guessing. It doesn't recoil or impact as hard as commercial .308.

 

[ParaElite]

One of the reasons I bought my DPMS LR 308 is that (according to what I was told) it will handle my Lake city match ammor and my Fed Match ammo. I have had no issues as yet. The Fed is more accurate though giving me sub moa. Whereas the Lake City stuff gives me 1 moa.

 

[wpnstech]

...one more linkie http://www.303british.com/id36.html

That link is from my site. I can confirm what tribbles said. It was put there for people that buy military surplus rifles like Ishapore 2A/2A1s or 7.62x51mm conversions like some of the early Mausers. As a retired service armourer, I got to inspect my share of rifles - both military and civilian. It boggled my mind to think that people would blindly trust some old clunker that they got at a bargain basement price. It was cheap for a reason!

New or used, headspacing is rarely an issue if you buy your rifle from a reputable shop that checks everything they have on their shelves. Unfortunately, many used or surplus rifles are not properly inspected before they hit the store rack.

Better safe than sorry.

 

[memphisjim]

ok this is a resurrection but i read the thread and i still am not sure
ill bring it to specific guns
dpms offers some of there lr308's as .308 chamber the lr308b for example
and some in 7.62x51mm the lr308c
as read above it seems that if the 308 will chamber in the nato round all is good
but putting a 308 in the nato chamber could be bad?
will either of these shoot it all?

 

[USSR]

as read above it seems that if the 308 will chamber in the nato round all is good
but putting a 308 in the nato chamber could be bad?
will either of these shoot it all?

Use either ammo in both of the chamberings of this particular rifle. Only downside of .308 in the 7.62x51 chambered DPMS, is possible short brass life.

Don

 

[Uncle Mike]

Here at Surplusrifle.com, we recommend in the strongest possible terms that you do not fire factory .308 Winchester ammunition in any Mil-Surp rifle chambered for the 7.62 NATO round.

This more than likely has to do with headspace problems more so than pressure differences.

Ruptured cartridges, separated rims...the Commercial stuff is lower pressure than the military ammo, so it is said, but I have heard of the exception.