7.62x51 can be fired in .308 and vise virsa right?


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younganddumb
July 7, 2008, 10:29 PM
Started a thread found out info on .308 but wondering can it be fired in a 7.62x51 and vise virsa?

Thanks guys for the help

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Bartkowski
July 7, 2008, 10:30 PM
A rifle chambered in .308 can shoot both, but one in 7.62x51 can't shoot .308.

esmith
July 7, 2008, 10:42 PM
.308 winchester generally fires with more pressure than 7.62 x 51 NATO. I wouldn't suggest shooting .308 and a rifle chambered in the NATO round, however some guns can handle the higher pressures.

spiroxlii
July 7, 2008, 11:00 PM
Like the two guys before me have already said...

A gun chambered for .308 Winchester can generally handle both.

A gun chambered for NATO standard 7.62x51 can't be guaranteed to safely shoot both, because commerical .308 Winchester cartridges may have produce higher peak pressures.

There are people on THR who will say that you really shouldn't worry about it. Some of us (myself included) have fired commercial .308 Win in rifles built for 7.62 NATO. I do it in my Ishapore 2A bolt action and have had no problems so far. That doesn't mean it's safe or recommended. It just means that it works, and at least with MY rifle, it hasn't caused a catastrophic failure.

I'm going to go out on a limb and say that the real problem with shooting .308 Winchester in a rifle chambered for 7.62 NATO is more related to increased wear and tear on the rifle rather than the risk of catastrophic failure. You may notice more accelerated wear in a semiautomatic battle rifle (since its operation depends on recoil energy generated by the ammunition) than you would with a bolt action military rifle like the Ishapore 2A (which is basically a Lee-Enfield No1MkIII made with more modern steel and chambered for 7.62 NATO).

pinstripe
July 7, 2008, 11:23 PM
I have shot them both from both chamberings with no big "KABOOM"! Ihave also never personally known anyone that has had any mishaps interchanging the 2 rounds. I have shot several thousands of rounds. Be your own judge and always know the condition of the rifle you are shooting. I only shoot this round from bolt action rifles, so I can't speak for semi auto rifles.

jonnyc
July 8, 2008, 12:50 AM
"A rifle chambered in .308 can shoot both, but one in 7.62x51 can't shoot .308."

Boy, then I guess I do the impossible every weekend!!!
This question gets asked WAY too often and the same spurious internet info gets repeated. The two rounds are essentially the same, and only RARELY will not interchange, usually military 7.62x51 not fitting into a tight commercial chamber.
Reloading is the problem, as hot .308 loads can be dangerous in military 7.62 brass, as it has thicker web brass and less internal capacity.

Bartkowski
July 8, 2008, 12:54 AM
I guess saying that you can't fire .308 in a 7.62 is wrong, but as a general rule you shouldn't fire 7.62 in a .308.

spiroxlii
July 8, 2008, 01:00 AM
I guess saying that you can't fire .308 in a 7.62 is wrong, but as a general rule you shouldn't fire 7.62 in a .308.

Not exactly. I think he was referring to the fact that although they have nearly identical outer dimensions, 7.62 NATO brass is thicker than .308 Winchester brass. That means that the NATO standard brass has a lower internal capacity than commercial brass. That's why hot .308 Winchester loads can produce higher pressures.

He is specifically cautioning against making hot handloads using 7.62 NATO brass.

goon
July 8, 2008, 02:38 AM
I generally also interchange the two. Sort of.
The rifle I shoot the most 7.62x51 in is a DSA STG-58. They were built on new DSA US made recievers but with Austrian STG parts. The barrels would have been chambered for 7.62x51mm, not .308. But the reciever is marked for .308 Winchester. I called DSA once and they told me that they do their testing with Portugese surplus (unless they ran out by now), which again, would have been 7.62x51. So for all intents and purposes, I don't worry about it much with this rifle.
But...
- My .308 handloads are always on the moderate side to keep them around the same specs as military surplus ammo. I do this so I don't have to adjust my sights or gas setting when switching between milsurp ammo and handloads.
- Any factory .308 I shoot will also be around the same weight as military surplus ammo. I tend to stick with bullets ranging from 147 to 168 grains. I could probably go up to 180 in my FAL and just take out the extra pressure by adjusting the gas, but in my position, I have no reason to bother with that. And I'd never even attempt to put something like a Light Magnum in my FAL.
- I've also been shooting some Black Hills Match ammo lately loaded with 155 grain Hornady A-Max bullets. I like this load because I found some at a reasonable price and because it sort of replicates Hornady TAP but saves me about $10 a box. I figure this ammo was originally intended for use in something like an M1A, so it's OK in my FAL. And that has proven to be the case.
- I have had trouble with hard chambering of some 7.62x51 in some .308 chambered rifles but I've never had any issues with .308 in a military surplus rifle. Probably a combination of the slightly different headspaces and of the better QC of commercial ammo.
- My Speer reloading manual doesn't distinguish between the two. It actually lists the .308 data as having been calculated and tested using IMI 7.62x51mm casings rather than commercial .308. It also cautions that military brass is usually thicker, resulting in less case capacity, which means that you need to make sure you aren't stuffing too much powder in it.

A lot of what you need to know about interchanging them though depends on what rifle you're using.
What rifle are you using?

35 Whelen
July 8, 2008, 02:56 AM
This issue was FINALLY put to rest some time back on another forum by a Technical Director of an ammo company. He was repeatedly challenged in the thread, but always, always was able to answer the questions and based everything he stated on fact. You can read it here: 7.62 NATO Pressure vs. commercial 308 Winchester (http://www.surplusrifleforum.com/viewtopic.php?f=76&t=39614&st=0&sk=t&sd=a")

If you take the time to read the posts, please do so with an open mind. As you'll see, there are plenty of buffoons out there who disagree regardless of the facts presented.
Regards,
35W

USSR
July 8, 2008, 10:36 AM
35 Whelen,

Thanks for that link. I have been arguing for years that while the 7.62x51's pressure is listed at 50k psi, it was established using the copper crusher method and is in fact a CUP measurement which puts it in the same pressure category as the .308 Winchester's 62k psi pressure spec using the piezoelectric method. The only real concerns about interchanging the ammo are: the lighter construction of some commercial .308 brass which may overly expand in a "generous" 7.62x51 chamber; and a possible platform limitation such as a M1 Garand converted to 7.62x51 or .308, in which the oprod cannot handle the higher port pressures generated by the slower burning powders used in most .308 commercial ammo.

Don

Candiru
July 8, 2008, 01:26 PM
The most important difference between .308 Winchester and 7.62x51mm NATO is the chamber in the gun. 7.62 NATO chambers are much longer than .308 Winchester, to the point that a NO-GO gauge in .308 Win is still shorter than a 7.62 NATO GO gauge. Firing .308 Winchester in a 7.62 NATO chamber is the equivalent of shooting it in a .308 Win rifle that will close the bolt on a field gauge with plenty of wiggle room left over. This is pretty much the definition of an unsafe gun/ammo combination.

7.62x51mm NATO gets away with these incredibly loose chambers because it has very thick brass. When the case flows under pressure, there are plenty of reserves at the base to ensure that enough brass remains to prevent gasses from rupturing the metal. .308 Winchester is much thinner because it's made in anticipation of a much tighter chamber; it won't have to flow much, so it trades the extra case material for higher capacity. Because of the higher capacity and the civilian powders used in many .308 cases, .308 tends to get better performance than 7.62x51mm NATO.

The performance difference, plus the fact that several sources list 7.62x51mm NATO as rated around 50K PSI and .308 Winchester at 62K PSI max, has led many to conclude that .308 Winchester is loaded to a higher pressure than 7.62 NATO. In reality, the 50K PSI figure came about because of different measurement techniques and mislabeling; it's really a CUP measurement, and 50K CUP translates to about 62K PSI. The difference in performance between .308 Win and 7.62x51mm NATO come from the former's increased case capacity. The real reasons not to use .308 Winchester in a 7.62mm NATO rifle are twofold: First, .308 Winchester can damage a military semi-auto built around the more sedate ballistics and pressure curves of 7.62mm NATO. More importantly, though, 7.62x51mm NATO chambers have far too much headspace to be safe shooting .308 Winchester ammo.

General Geoff
July 8, 2008, 01:48 PM
The real reasons not to use .308 Winchester in a 7.62mm NATO rifle are twofold: First, .308 Winchester can damage a military semi-auto built around the more sedate ballistics and pressure curves of 7.62mm NATO. More importantly, though, 7.62x51mm NATO chambers have far too much headspace to be safe shooting .308 Winchester ammo.

My M1A has a head space of 1.631. While the rifle is advertised as being chambered for 7.62mm NATO, this is technically out of spec (7.62 chamber GO spec is 1.634, afaik). But it also means that it can safely chamber and fire both 7.62 and .308 ammo, no problem (gas system pressures notwithstanding).


The bottom line is to get your rifle's headspace measured before you go firing .308 in an old, worn 7.62 marked rifle.

spiroxlii
July 8, 2008, 01:52 PM
After reading everything here, I've decided to continue using both 7.62 NATO and .308 Winchester in my Ishapore 2A bolt action. I WOULD NOT DO THIS if I collected my brass for reloading, since thin commercial brass might deform too much in a loose military chamber, but with new brass I'm not concerned about a rupture.

goon
July 8, 2008, 02:07 PM
35 Whelen - Thank you.
That is about the most informative discussion on this topic I've ever seen. I added it to my Favorites.

younganddumb
July 8, 2008, 07:13 PM
thank you 35 whelen my head is some what clearer... maybe....

SMLE
July 8, 2008, 08:52 PM
http://www.smellysmleshooters.net/ammopressure.htm

Onmilo
July 8, 2008, 10:53 PM
You can generally shoot .308 commercial in a 7.62X51 chambered rifle as long as you stay with bullet weights no heavier than 168 grains.

If you reload .308 cartridge cases fired in a 7.62X51 chamber, it is strongly recommended that you anneal the case prior to resizing every time and limit the number of reload cycles to two.

7.62X51 is generally not recommended to be fired in a commercial .308 chamber mainly because of the longer headspace dimension and thicker brass of the NATO specification cartridge.
This will usually result in a stuck bolt sooner or later.
The pressures the cartridges develop are similar if the bullet weights are kept below 168 grains and the shooter is not trying to use high pressure commercial .308 Winchester cartridges, i.e. 'light magnum'.

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