Interchanging .308 win and 7.62x51 NATO

Calibres, cartridges, ballistics tables and ammunition information.

Re: Interchanging .308 win and 7.62x51 NATO

Post by MeccaOz » 12 Nov 2014, 9:15 am

Yup thats right mate, in general anyways :)
User avatar
MeccaOz
Warrant Officer C2
Warrant Officer C2
 
Posts: 1013
Western Australia

Re: Interchanging .308 win and 7.62x51 NATO

Post by Chronos » 12 Nov 2014, 9:16 am

Correct.

Just to confuse things it's the other way around with 5.56X45 v .223

Chronos
User avatar
Chronos
Second Lieutenant
Second Lieutenant
 
Posts: 2082
New South Wales

Re: Interchanging .308 win and 7.62x51 NATO

Post by Warrigul » 12 Nov 2014, 10:25 am

sudes wrote:Just checking I have this right...

You can fire 7.62x51mm NATO rounds in a rifle chambered for .308...

But you can *not* fire a .308 cartridge in a rifle chambered for 7.62 NATO because the .308 cartridge generates more pressure?

Right or wrong?


It is not simply about pressure, but that is the main reason when you talk about old 93 mausers, #4 enfields etc etc. but 7.62 x 51 military chambers are oversize to allow for mud, poor cleaning, extended firing, automatic operation etc.

7.62 military brass has a thicker case to compensate. If a thin walled .308 is fired in a 7.62 chamber then case seperations are more likely. This is a known fact.

Simply downloading .308 may not be enough to be safe unless you have checked the headspace as well.

You may have a nice strong K98 Israeli in 7.62 x 51, it may even have matching numbers BUT:

Have a look at the guage differences:


308 Winchester Gauges
GO - 1.6300"
NOGO - 1.6340"
FIELD - 1.6380"

Military Gauges
GO - 1.6350"
NOGO - 1.6405"
FIELD - 1.6455"

Pretty scary.........................


I haven't been down this path for a while so any corrections would be appreciated.
Warrigul
Warrant Officer C2
Warrant Officer C2
 
Posts: 1103
-

Re: Interchanging .308 win and 7.62x51 NATO

Post by ghunther » 12 Nov 2014, 2:36 pm

Warrigul wrote:7.62 military brass has a thicker case to compensate. If a thin walled .308 is fired in a 7.62 chamber then case seperations are more likely.


Bit off topic here but if you can tell me. If reloading fired .308 brass could you set the die a fraction higher to not bump the shoulder and close up the headspace?

Theoretically...
ghunther
Recruit
Recruit
 
Posts: 22
South Australia

Re: Interchanging .308 win and 7.62x51 NATO

Post by Old Fart » 12 Nov 2014, 2:42 pm

The problem as Warrigul rightly says is headspace.

Because pressure alone is problem enough often a lot of the explanations end there as further factors don't really matter.

The problem is modern firearms designed to handle higher pressures have come along and solved the pressure problem, but the headspace issue has been forgotten.

When chambering a .308 cartridge in a firearm chambered for 7.62 NATO which will withstand higher pressure there is still an excess of headspace.

To further cloud it there are now firearms which all but directly say they are the same thing. e.g. The Ruger SR-762 is - and I quote from the Ruger website - "Chambered in .308 Win./7.62 NATO". It goes on to say "bringing the .308 Win./7.62 NATO cartridge".

Anyone who read that would reasonably take it to mean they are the same cartridge, and coming from an authority like Ruger there isn't really any reasons someone shouldn't just accept it an move on. But they're not the same cartridge.

If someone reads that then go back to and old rifle, half informed, they could be in trouble.
Winchester Model 70 Featherweight - .270 Winchester Short Magnum
Uberti 1873 Short Rifle - .45 Colt
Winchester Model 70 Coyote Varmint - .22-250 Remington
User avatar
Old Fart
Corporal
Corporal
 
Posts: 261
South Australia

Re: Interchanging .308 win and 7.62x51 NATO

Post by Warrigul » 12 Nov 2014, 2:46 pm

ghunther wrote:Bit off topic here but if you can tell me. If reloading fired .308 brass could you set the die a fraction higher to not bump the shoulder and close up the headspace?

Theoretically...


You are on the ball.

This is what I do already for my target rifles, I only ever full length size just enough to allow the bolt to close easily. Each rifle is different and the dies should be adjusted accordingly. But once you have fired the case if you do nothing else other than neck size then that case now has perfect headspace for that rifle(as long as the case hasn't cracked or neck split).

I also only neck size .303, hence I have a perfect match for the chamber and the brass doesn't have to stretch at all. A .303 is headspaced on the rim but the chambers are usually oversize so once they have done the big stretch there is no reason to squash them all the way back down just to stretch their guts out again. The less stretching and squashing you do the longer the case will last.


I think this is worth a topic all of its own so will dig out some info and the mods can post a link, might take me a day or so as I am manually pricing parts from a parts list for stocktake and I have 14,000 odd parts to go.
Warrigul
Warrant Officer C2
Warrant Officer C2
 
Posts: 1103
-

Re: Interchanging .308 win and 7.62x51 NATO

Post by jeener » 14 Nov 2014, 11:54 am

Old Fart wrote:To further cloud it there are now firearms which all but directly say they are the same thing. e.g. The Ruger SR-762 is - and I quote from the Ruger website - "Chambered in .308 Win./7.62 NATO". It goes on to say "bringing the .308 Win./7.62 NATO cartridge".

Anyone who read that would reasonably take it to mean they are the same cartridge, and coming from an authority like Ruger there isn't really any reasons someone shouldn't just accept it an move on. But they're not the same cartridge.

If someone reads that then go back to and old rifle, half informed, they could be in trouble.


Doesn't look good on the marketing material to have a safety lesson about other rifles so they leave it off. Just have to be responsible for their rifle standing up to both I guess. A bit iffy though.
jeener
Private
Private
 
Posts: 56
New South Wales

Re: Interchanging .308 win and 7.62x51 NATO

Post by Old Fart » 14 Nov 2014, 11:59 am

I'm not suggesting the Ruger is unsafe, I honestly know nothing about the SR-762 other than what I copied and pasted above for the example.

They're renowned for their strong actions and I'm sure the SR-762 does exactly what it claims and does it safely. They'll be looking out for themselves and their customers I'm sure.

But yes, on the subject of the cartridges themselves it does nothing to help clarify that the two are different enough to have serious safety concerns in certain situations.
Winchester Model 70 Featherweight - .270 Winchester Short Magnum
Uberti 1873 Short Rifle - .45 Colt
Winchester Model 70 Coyote Varmint - .22-250 Remington
User avatar
Old Fart
Corporal
Corporal
 
Posts: 261
South Australia


Back to top
 
Return to Calibres, cartridges and ballistics