.308/7.62x51????

[jworm1420]

Ok i think i know the answer to this but just wanted to be sure. I know that if you have a ridfle chambered in 5.56 you can use a .223 rd, as the dimemsions of the brass being slightly different. But niot the other way around. And i am pretty sure that idea applies for a rifle chambered in .308, you can shoot a 7.62x51 cartridge in out of it. That correct??? Also what about 7.62x54, and whats the difference between 7.62x51 and 7.62x54?? Can someone please just clarify so i dont screw something(myself) up. Thanks.

 

[kludge]

.308 Win can be loaded to higher pressure than 7.62 NATO - it can be hard to tell though, trying to interpret kCUP vs kPSI numbers.

It's generally not recommended to fire .308 Win in some 7.62 NATO rifles, the Ishapore comes to mind. I doubt you would have any problem with an AR-10 though.

5.56 NATO is loaded to higher pressure than .223 Rem. Rifles chambered for 5.56 have more leade in the chamber (distance before the bullet contacts the rifling) to keep chamber pressure down, and also has more "room" all the way around for better feeding and extration, which is much more important than accuracy on the battlefield. and that also reduces chamber pressure.

However I suspect that in today's litigious society ALL rifle makers are aware that 5.56 and .223 case dimensions are the same and chamber their rifles accordingly. Exactly what those dimensions are is a mystery, and to know for sure you would have to do a chamber cast of your particular rifle.

I have no proof though. *I* would have no qualms about firing 5.56 out of a .223 chamber, but several others will disagree with me. But then, I wouldn't go shooting Wolf/Golden Bear/Tula through a .223 bolt gun anyway. Bi-metal bullet jackets and all.

 

[Indy_Guy_77]

.308 Win can be loaded to higher pressure than 7.62 NATO - it can be hard to tell though, trying to interpret kCUP vs kPSI numbers.

The line/s between .308 and 7.62NATO are blurry, fuzzy, and hard to interpret - all at the same time.

Many folks think that the differences between the two are much smaller than the difference between .223 and 5.56NATO.

If you have an old military rifle chambered in 7.62NATO - I'd not fire any commercial .308 out of it. Handloads - sure - if they were "light". I'm sure that for most all modern weapons - it wouldn't be a big deal. Defining "modern", however, may not be all that easy.

When in doubt, read the owner's manual. Do what it recommends.

-J-

 

[jworm1420]

i will definatley read the owners manual, but what about a bolt rifle chambered in .308??? Technically its safe to fire a 7.62x51 out of that correct. Im only asking because 7.62x51 is cheaper than .308. That will only matter for a short time to me until i can get some extra $$$ to get a die set for .308. And as stated before whats the difference in 7.62x51 and 7.62x54???? And is it sfae to shoot 7.62x54 out of a rifle chambered .308???? Just trying to learn......

 

[BigMoose]

Any more, with the two calibers. They cut compromise chambers on newer firearms.

Even with the old chambers, if your not reloading brass. I wouldn't worry. (7.62x51/308)

The ones to watch are 308 MATCH chambers. They tend to be tight and could cause some issues with surplus 7.62x51.

As to 7.62x54R, HELL NO, that is a rimmed Russian cartridge

They sell head space gauges for 308 and 7.62x51. If your really worried, test your chamber with those.

 

[sloughfoot]

It is safe to fire 7.62 Nato in a .308 chambered gun.

It is not POSSIBLE to fire 7.62X54 out of a .308 chambered gun. There is no way to get the bolt to close on the chambered cartridge. (rimmed case, 3mm longer...)

 

[jworm1420]

thank you guys for the info, much appreciated.

 

[kludge]

Many folks think that the differences between the two are much smaller than the difference between .223 and 5.56NATO.

And how big of a difference can there be when the CIP specifies the SAME pressure for proof loads for both the 5.56 and the .223?

Unless there some factor I'm not thinking of.

 

[Slapstick]

NATO 7.62 is safe to shoot in any gun chamber for .308 Winchester. It is not safe to shoot .308 Winchester in a gun Chambered for 7.62x51 NATO. .308 average chamber pressure is 62,000 psi for 7.61x51 NATO it's 58,000 psi.

While a bolt gun may not notice a difference a semi auto designed for 7.62x51 will. Most new semi auto's are either tuned to work with 7.62x51 NATO only or they have a gas regulator to allow them to fire .308 Winchester without damage. It's all about the pressure and the .308 is loaded to higher average pressure than the 7.62x51 NATO.

 

[kludge]

I've seen anywhere from 50,000 psi to 60,200 psi quoted for 7.62x51.

The number I see most often is 50,000 psi. Wikipedia has the 62,000 number.

The numbers I believe to be true:
50kpsi for 7.62 NATO
62kpsi for .308 Win

For MIL-SURP rifle the distinction is VERY important, and again rifles like the Ishapore and the FR8 should not be used with .308 Win ammo, IMO.

Now, and here is the question that no one can answer except the factories with pressure testing equipment...

The NATO chamber is 0.013" longer than the .308 Win chambers.
A 7.62 go-gauge is 1.6350"; no-go is 1.6405"
A.308 go gauge is 1.6300"; no-go is 1.6340"

... so a 7.62 chamber will close on a .308 Win no-go gauge. Would this difference alone reduce pressure enough to safely shoot .308 Win? The world may never know.

Here's what I conclude: A company can't build a rifle with a 7.62 chamber and stamp .308 Win on the barrel because it's not within SAAMI spec, regardless of whether or not it's safe to use .308 Win ammo.

So for modern rifles, if there is any question (i.e. the barrel is marked 7.62 and you wonder if .308 Win is safe), call the manufacturer and ask.

For reloading...
... if using commercial brass in Mil-Surp rifles, usually .308 Win start loads are fine. (BUT check the listed start pressure!)
... when using NATO brass, reduce loads by 2gr (per Sierra manual) because the thicker NATO brass increases chamber pressure. This goes for 7.62x51 and .308 Win loads.

 

[Mr Evilwrench]

.223 in 5.56 yes
5.56 in .223 no, pressure too high, you'll be picking the chamber out of your face with tweezers.
.223 or 5.56 in .223 Wylde yes
7.62x51 in .308 yes
.308 in 7.62x51 no, see above.
7.62x54 is right. out. It's a rimmed cartridge that's too long for 7.62x51. It's for your Mosin or Dragunov or PSL or whatever.

 

[kludge]

I've been doing some more research, just for my own pleasure, and I've found a couple interesting links, so I though I would share...

Proof Loads | The Shooter's Log

^I might need to pick this up and read the full article. Patrick Sweeny usually does a pretty good job,

5.56mm (5.56 x 45 mm) Ammunition

^ shows the Mil-Spec chamber pressure for the M193 and M855 -- the most common 5.56 ammo that we shoot. They are listed at 52kpsi and 55kpsi, respectively. But the Mil-Spec method of pressure measurement is different than SAAMI, so keep that in mind.

http://www.luckygunner.com/labs/5-56-vs-223/

^ actual pressure testing of 5.56 and .223 ammo in .223 and 5.56 chambers.

(not surprisingly, no rifles blew up)

 

[cwagner1]

Just read your firearms manual. Mine specify that I can use .308 and 7.62x51, and specify a maximum and minimum operating pressure. Yours may be different.

Consult your reloading manual to see if you are within the firearm manufacturers spec.