Are there any major saftey issues with running 7.62x51 in a .308 Bolt gun???


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cslinger
November 11, 2003, 03:38 PM
Topic sums up the question. I realize that commercial .308 is slightly different then 7.62x51 but are there any saftey issues with running surplus 7.62x51 through a bolt gun chambered in .308. I would assume not since the .308 runs at a higher pressure, does it not?

Thanks
Chris

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Andrew Wyatt
November 11, 2003, 03:54 PM
the only functional difference between .308 and 7.62X51 is the pressure.

cslinger
November 11, 2003, 05:46 PM
Am I correct in my assumption that most commercial .308 runs at a higher pressure than most 7.62x51 Nato?

Thanks
Chris

Pheonix
November 11, 2003, 05:51 PM
I share your opinion but have no facts to back it up.

Jhaislet
November 11, 2003, 07:17 PM
I tried a couple rounds of a Portugies 7.62x51mm battle pack in my 700LTR .308 and it was harder'n hell to extract. It loaded up just fine, but after firing it was almost impossible to remove the fired brass. I've had enough of that crap. I shoot Georgia Arms "Canned Heat" exclusively in this rifle now. Its definately sub-MOA with this ammo. It pushes a 168gn Sierra BTHP @ 2650fps and almost all the brass is LC or Win. 500rnds is $190 +s/h.

Jim K
November 11, 2003, 10:29 PM
I never had a problem with Portuguese ammo, but had a lot of stuck cases in an FAL with South African ammo until I polished the chamber.

I have fired rifles both ways, don't really care which goes where, and have had no problems either way. The maximum working pressure spec for the .308 exceeds that of the 7.62 NATO, but it is not the practice of ammo companies to load to maximum. Nor is any good rifle going to "blow up" with even that maximum working pressure. (I would be careful with .308 rifles converted from 7x57, though, as they were never made for more than a 40k or so pressure level and can develop excess headspace from higher pressure loads.)

Jim

twoblink
November 11, 2003, 11:57 PM
I think the pressure is the only difference too..

<Insert Art here>

Someone will post SAMMI pressure specs for 308 vs 7.62x51 hopefully here..

Publicola
November 12, 2003, 03:23 AM
Actually pressure is not the only difference between the 7.62x51mm & the .308 Winchester.

The headspace (both chamber & cartridge) is different between the two, with the 7.62x51mm chamber being a bit longer at 1.6355"(min.) to 1.6455"(field reject) vs. the .308 Winchester chamber at 1.630""(min.) to 1.638(field reject).

The cartridge headspace is a little different than the chamber headspace regarding these two respective cartridges, as the 7.62x51mm cartridge headspace (1.630" to 1.633") falls within the upper end of the .308 Winchester cartridge headspace range (1.627" to 1.633"). So using 7.62x51mm ammo in a .308 isn't that bad as long as the .308 Winchester chamber is +.002" from the minimum of 1.630". If it's at minimum or +.001" then there's a chance you'll have a negative headspace situation when trying to chamber a 7.62x51mm cartridge.

So as long as your bolt gun has a chamber headspace of at least 1.632" then running 7.62x51mm ammo should be no problem. Wiht a semi make double-damn sure the chamber is at least 1.632".

But under no circumstances should you try to run .308 Winchester ammo in a 7.62x51mm chambered rifle.

Master Blaster
November 12, 2003, 10:02 AM
Both my speer #13, and Lyman manuals seem to think that they are the same round.?????????

Could they be mistaken????

Kestrel
November 12, 2003, 10:12 AM
Jim,

How do you polish the chamber (as on an FAL)?

Publicola,

People fire .308 Win. in 7.62x51 rifles all the time. What is the potential problem with it?

Thanks,
Steve

FireInTheHole
November 12, 2003, 10:32 AM
Some .308 are near the max pressure. Compared to a 7.62x51mm a full power .308 is a proof load. Do you really want to shoot a bunch of proof loads through a 50 year old rifle that close to your head?

If you want hunting ammo for a 7.62 nato, pull the heads and replace with sp bullet of similar weight. JMO.

cslinger
November 12, 2003, 12:03 PM
Thanks guys just what I thought. Heck I will probably never fire a 7.62 NATO round out of my bolt gun but just wanted to make sure my knowledge was up to date as far as whether I could.

I had also read that the NATO rounds headspaced slightly differently and that could cause some minor case swelling making it harder to extract.

Thanks for the info.

Chris

Andrew Wyatt
November 12, 2003, 02:17 PM
The headspace (both chamber & cartridge) is different between the two, with the 7.62x51mm chamber being a bit longer at 1.6355"(min.) to 1.6455"(field reject) vs. the .308 Winchester chamber at 1.630""(min.) to 1.638(field reject).


That's like saying that commercial .303 brit and military .303 brit are different rounds, though. The saami and british military headspace gauges are different for .303, with the military having a much longer headspace allowance for field reject.

Dr.Rob
November 12, 2003, 06:14 PM
Publicola did the best job of justifying/explaining this I've ever seen. But i'm still not sure I agree.


Translation:

Military rifles have more 'slop' room built in.
Commercial rifles don't.

The ammo is the same, unless someone starts tinkering with the OAL to bridge the gap in a military chamber. (and thereby get better accuracy)

You can also bridge that gap by not re-sizing properly, as one might find in inexpensive reloaded (military remfg ammo.)

Never seen an American rifle marked .308 come with a warning NOT to shoot 7.62 nato in it, or vice versa. Don't you think that's a pretty obvious warning to overlook?

So please... if anyone has an owners manual that states this either way, PLEASE share it.

Publicola
November 12, 2003, 07:01 PM
SteveW13,
The problem is excessive headspace. If you have a minimum 7.62x51mm chamber, which would measure 1.6355" & you chamber a .308 Winchester cartridge that measures 1.630" you'd have .0055" under the headspace requirements of that chamber. Now .0055" might not be that bad, but what if the 7.62x51mm chamber isn't a minimum? Let's say it's 1.640". That'd leave .010" for the cartridge to expand to fill. Keep in mind there's only a .010" difference between the 7.62x51mm minimum chamber headspace of 1.655" & the field reject headspace of 1.645". The military thinks that is too much of a gap to fill with thicker brass only meant to be fired once.

7.62x51mm ammo has a headspace of between 1.630" & 1.633" with 1.632" being a workable average. Now a 1.632" cartridge in a field reject 7.62x51mm chamber (1.645") would have .013" to expand & fill. (keep in mind field reject means the headspace is too excessive & shouldn't be used, & that military brass is more robust & typically only fired once). It'd only have .0035" to fill in a minimum spec chamber (1.6355") & for it to reach the .010" mark the chamber would be real close to field reject (1.642" which is only .0035 away from field reject).

Commercial brass simply isn't up to that amount of stretching. Not safely, or safely enough for me.

Now some people do fire .308 Winchester brass in 7.62x51mm chambers & suffer no ill effects. I would guess that their brass life ain't what it could be due to the excessive stretching. But it's just like redlining handloads; some people get away with it, but some don't.

One fortunate thing is that most gunsmiths are headspacing 7.62x51mm chambers to 1.632" which more or less eliminates the problem. But ya have to watch the surplus rifles that are probably headspaced to true 7.62x51mm specs (minimum of 1.6355").

Another thing that possibly lets some get away with it is that bolt guns are very forgiving. The cartridge expands & contracts before any effort is made to remove it from the chamber. With gas operated semi's the bolt starts trying to remove the cartridge from the chamber before it's had a chance to contract. This makes case head seperation likely as the brass is already stretched thin by the oversized (for it) chamber just as the extractor starts applying force to remove it.

MasterBlaster,
I've heard the reloading manual argument before. It's not that the manual is wrong; it's that you're looking at it the wrong way. A reloading manual will give cartridge dimensions, not chamber dimensions. 7.62x51mm cartridges fall in the upper end of .308 Winchester cartridge specs. So for the manuals purposes the two cartridges are the same. You resize brass between 1.627" & 1.633", which is within .308 Winchester specs. They assume you are using it in a .308 Winchester or .308 Winchester sized chamber & that you're aware of the headspace you're working with.

So they're not mistaken; they just deal with the cartridge aspect of reloading & not the chamber headspace.

Andrew Wyatt,
To tell the truth I'm not familiar with the .303 British cartridge but that doesn't surprise me. In fact the .30-06 has different headspace dimensions for military vs. commercial specs. In the '06's case (bad puns always intended) the difference is so minor that it's inconsequential.

There's also a difference between the .223 Remington & the 5.56x45mm & it wouldn't surprise me if almost all military rifle cartridges had different headspace specs than their nearest commercial equivilent.

But as far as I am aware the '06 is the only one that is safely interchangable between military & commercial specs. Everything else is not safely interchangable.

The main thing is to know your headspace dimensions, both cartridge & chamber & then decide if it's a safe combination. It should be noted that not having enough headspace (such as trying to fire a 7.62x51mm cartridge that measures 1.632" in a .308 Winchester rifle that measures 1.630") is much more dangerous than having excessive headspace, especially in semi's. But personally I wouldn't play around with either extreme. A ruptured or even stuck case may be preferable to an out of battery or slame fire, but it's just not as acceptable to me as sending some rounds downrange w/o any incidents on the firing line.

For more reading on the headspace differences of the 7.62x51mm & the .308 Winchester, I invite you to examine the following links:

http://outdoorsbest.zeroforum.com/zerothread?id=87590

http://www3.sympatico.ca/shooters/7_62vs308.htm

http://www.armalite.com/library/techNotes/word97_docs/tnote11.doc

http://www.thegunzone.com/30cal.html

Jim K
November 12, 2003, 09:30 PM
Hi, Publicola,

If you are correct, rifles should be blowing up all over the place, and case bursts should be heard from sea to shining sea. But that is not happening. If ammo companies always load .308 to the absolute maximum working pressure, and all semi-auto chambers are too tight, a lot of folks are in trouble.

Forgive me for thinking you are into playing with numbers and take the headspace question way too seriously. When it gets down to ten thousandths of an inch, we are into the "angels on the head of a pin" type of argument.

Hi, SteveW13,

To polish an FAL chamber, I just used some 600 grit paper in a slit dowel rod. Don't overdo it; a light polish is enough. Otherwise, you might take off .000000003" too much and Publicola will get after you.

Jim

Dave R
November 12, 2003, 11:49 PM
Agree with Master Blaster. Speer 13 says .308Win is commercial version of 7.62X51. They say reload that mil-spec brass, just make sure you remove the primer crimp. They also say milspec brass is thicker, and case capacity is slightly less, so download load data slightly to accommodate the smaller case.

But that certainly implies that its OK to shoot that brass in your hunting rifle.

I have fired @ 100 or 200 rounds of milsurp in my Rem 700. No extraction problems, no pressure signs. 'Course, I only shot the "good" milsurp. Portugese (FNM), Radway and Hirtenberger.

Publicola
November 13, 2003, 08:44 AM
Jim Kennan,
Maybe I explained too much. Here's the short version:

A 7.62x51 chamber headspace is longer than a .308 Winchester chamber by enough to make a difference.

7.62x51 cartridge headspace is just a little bit longer than .308 Winchester cartridge headspace on average, though it's in the upper end of the >308 Winchester cartridge headspace specs.

So a .308 Winchester cartridge will probably be too short to function safely in a 7.62x51 chamber, especially considering that .308 Winchester brass isn't as sturdy as mil-surp 7.62x51 brass.

A 7.62x51 cartridge will be too long to function safely in a minimum headspace .308 Winchester chamber, but it should be fine as long as the headspace is 1.632" or longer.


Now a lot of people exchange the two different types of ammo freely in both kinds of chambers & you do not hear about blow ups everyday. In fact they're pretty rare. That doesn't mean it's safe to switch the two cartridges, it means a lot of people have better luck than they think.

But like I said, a lot of people redline loads (i.e. load above maximum powder charge, seat bullet too deep for a given powder charge, etc...) & you don't hear about them blowing up rifles & pistols everyday. That doesn't mean it's safe to redline a load, it just means a lot of people get away with it.

But what I do bet is common is very short brass life for the reloader who uses .308 Winchester ammo in a 7.62x51 chamber. & that's something that you wouldn't hear about as most people would blame it on that particular rifle or lot of brass rather than the headspace difference between chamber & cartridge.

& when it comes to headspace, 0.01 is a big deal. There's only a 0.01 difference between minimum & maximum headspace in the .308 Winchester. But don't take my word for it; ask any gunsmith you know if a .308 Winchester chamber .01 longer minimum headspace is safe to continue using.

& for the record I don't get on anyone who polishes their chamber until it gets to be .00000003" too large. :cool:

Dave R,
Reloading manuals deal with cartridge dimensions, not chamber dimensions. Any 7.62x51 brass you resize will be resized to .308 Winchester specs. The only difference in cartridge headspace between the two is that 7.62x51 brass is within the upper end of the .308 Winchester cartridge length range.

Reloading manuals do not get into detailed discussions about chamber headspace. It's not their purpose; they just deal with cartridges. & since the reloading process will flatten out any differences in cartridge headspace it's a moot point for them to get into. The main difference is the chamber dimensions, not so much the cartridge dimensions.

& from a certain point of view they are right that the two cartridges are basically the same, since the 7.62x51 is within the cartridge headspace range of the .308 Winchester; it's just held to the upper end of that range. It's kinda like saying match ammo is the same as regular ammo in that cartridge; it's within specs but held more towards one end than the other.

But it's important to realize that 7.62x51 cartridges are held on the upper end of the acceptable range.

If you've fired 7.62x51 ammo in your bolt gun, I'd say chances are your chamber is at 1.632 or longer, though it could be right at minimum. Bolt guns are much more forgiving of cartridge differences than semi's are. & when you resize those 7.62x51 cases, they go through the same die (adjusted the same way) as your .308 Winchester cases right? That means they're resized within the .308 Winchester tolerances (which they were within to begin with). Then you trim the brass right? & you trim it to the recommended length for .308 Winchester. So for all the reloads the only difference between commercial .308 Winchester cases & your resized 7.62x51 cases is that the 7.62x51 cases are a little thicker.

& most gunsmiths & gun makers that I know don't make .308 Winchester chambers right at minimum unless it's a special order. Usually it's 1.632 or so instead of 1.630. This would eliminate any problems with firing mil-surp 7.62x51 in a .308 chamber.

The most important thing is to know the headspace of your chamber. That'll let you know if you should be concerned about it or not. & it's important to know the differences between the cartridges so you can decide if your chamber is safe to interchange ammo.

I'm not saying you can't fire 7.62x51 in a .308 chamber; I'm simply saying you should know exactly what you're working with before you do. Make sure your chamber headspace is 1.632 or longer & you should be fine.

I am saying you shouldn't fire .308 Winchester in a 7.62x51 chamber. It's not worth the risk.

Dave R
November 14, 2003, 02:04 PM
Publicola, thanks for the simplified explanation.

It leads me to another question, though.

Why in the world would the two cartridge specs diverge when they started out the same? .308Win is the commercial offering of 7.62X51 right?

So did the military adopt a bigger chamber for more reliability? And the commercial arms makers went to tighter chambers for accuracy? And the two then wound up just enough different to cause long threads on discussion boards for something that seemed apparent in the first place?

My understanding is that .223 and 5.56X45 have pretty much the same differences, right?

Oh, yeah, and to make things more confusing, I have bought Winchester White Box 7.62 in the past , that appears to be NATO spec ammo. Labeled Cal 7.62mm. Headstamp is WCC 87. Sealed primers (but no primer crimp), and NATO-style crimp marks on the case mouth. Sold through commercial firearms vendors. No warnings to not use them in .308's. Just adds to the confusion.

Publicola
November 15, 2003, 03:08 AM
Actually Winchester developed the .308 Winchester a few years before the military adopted the 7.62x51. It's not that they were both created at the same time; one pre-dates the other. I assume that the military went with slightly larger chamber dimensions for reliability in semi's, as the rifle at the time was the M14. They kept the cartridge dimensions within .308 Winchester specs, but held them to the upper end of those specs. They wanted a larger chamber to help with extraction & negate any possibility of cartridges with negative headspace being chambered.

So the commercial makers stuck to the original chamber & cartridge specs for the .308 Winchester while the military went to a slightly larger chamber & kept the ammo on the upper end of .308 Winchester specs.

As to the 5.56x45 & the .223 Remington, they too are different. I'm not that up to date on the specifics (as I'm not a big fan of the AR or its cartridge) but here's a link that goes into more detail on it

http://www.thegunzone.com/556v223.html

Now as far as a lack of warnings on various ammo boxes I agree that because of the confusion surrounding the calibers in question specific warnins should be placed on the boxes. However I just checked 3 boxes of '06 ammo & they each had warnings to the effect of only using that cartridge in firearms chambered for that cartridge (or in one case, only use this cartridge in firearms whose markings exactly match those of the cartridge). So there are sufficient warnings on the boxes already. 7.62x51 is a different designation than .308 Winchester, just as 5.56x45 is a different designation than .223 Remington.

I do recall on at least one Springfield M1a I was examining in a store that there was a big warning tag on the trigger saying to only use 7.62x51 ammo.

As another interesting aside were you aware that 7.62x39 cartridges usually have a bullet that's .311 in diameter? But Ruger was making Mini-30's with a .308 diameter bore & a lot of american cartridge manufacturers make 7.62x39 ammo with a .308 bullet. No biggie to shoot .308 bullets in the .311 bore of an SKS or AK, although accuracy won't be spectaculer. But launching a .311 bullet down a .308 bore is not a good thing. Yet most people aren't aware of this either.

SAAMI & the various manufacturers probably should make more of an effort to make people aware of these differences. But then again I always felt it was the responsibility of the shooter to know exactly what he was dealing with, whether SAAMI or anyone else was willing to educate them or not.

Incidentally I first found out the differences in the 7.62x51 & the .308 Winchester from reading Jerry Kuhnhausen's The U.S. .30 Caliber Gas Operated Service Rifles , A Shop Manual , Volumes I & II. http://www.midwayusa.com/rewriteaproduct/582340

I have no real dog in this one, as I prefer '06 Garands to 7.62x51 or .308 Winchester M14/M1A's, but I was surprised to learn this as I too thought they were the same.

Mannlicher
November 16, 2003, 06:44 PM
Publicola, I have run a lot of Federal 150 grain Classic SP through my M1A, and it likes it just fine. I just measured a lot of Portugese, Winchester, and Indian 7.62 X 51 ammo, and compared it to some Federal, and Remington commercial ammo. I can't find any difference.

SMLE
November 28, 2003, 09:23 AM
Check out this link...

http://www.smellysmleshooters.net/ammopressure.htm

Very good info.

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