.308 vs 7.62 NATO question


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borrowedtime69
May 3, 2007, 02:43 AM
i have an old Marlin (with western auto / revelations name) in .308 Winchester. can you shoot both .308 Winchester and 7.62 NATO out of the hunting bolt action? im looking to see if the cheaper mil-surplus ammo would work in my gun. i've heard that you cannot shoot the hunting .308 round out of a military 7.62 ammo cause it has higher pressures? thank you for your help -Eric

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M92FS
May 3, 2007, 03:01 AM
No , you cannot shoot 7.62 x 51mm cartridges with your old marlin due to the higher pressure of the 7.62 x 51mm cartridge.

ps : If you have a semi-auto rifle with 7.62 x 51mm markings , you can shoot .308 cartridges.

Warbow
May 3, 2007, 04:17 AM
No , you cannot shoot 7.62 x 51mm cartridges with your old marlin due to the higher pressure of the 7.62 x 51mm cartridge.

ps : If you have a semi-auto rifle with 7.62 x 51mm markings , you can shoot .308 cartridges.

That's wrong.

The main difference is in the chamber dimensions.

A .308 chambered rifle shouldn't have any problem firing 7.62 NATO ammo. .308 Winchester has a SAAMI max. pressure of 62,000 PSI, while 7.62 NATO's is listed as 50,000 PSI for M2 Ball in the US Army tech. manual (http://www.kmike.com/Ammo/tm%2043-0001-27.pdf).

Where problems can occur is when using .308 Winchester in 7.62 NATO chambered rifles. Since the 7.62 chamber is longer than a .308 chamber, creating a larger headspace, the thinner brass thickness of .308 can possibly cause case head separation when fired in a 7.62 chamber.

nwilliams
May 3, 2007, 04:36 AM
This might help you:

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

cdrt
May 3, 2007, 08:06 AM
Thanks for posting the link to that article on the .308 Win and 7.62 NATO cartridges. I am now enlightened.

I have some LC 90 that I've shooting out of my .308 converted M1. Glad to know I wasn't doing something that was bad for the rifle.

Navy Vet & SWIFT Boat OIC

Jim Watson
May 3, 2007, 08:09 AM
If the Army is getting 2750 fps at 50,000 psi why is Remchester not getting about 3100 at 62,000 psi? (Rule of thumb confirmed by Vihtavuori, the increase in velocity is about half the increase in pressure.)

Answer: The Army still goes by crusher gauge readings but since they are not a member of SAAMI do not recognize the CUP terminology and report crusher data in psi. When the round(s) were introduced, the .308 Winchester was specified at a maximum of 55,000 psi (pre CUP crusher data) and a standard of 52,000. You will find 2000 psi difference in cartridges out of the same box, and 5000 difference from lot to lot.

I guess you could run into trouble if you reloaded minimum commercial cases shot in a maximum military chamber, which might become a problem when people realize that whining about the lack of cheap foreign ammunition is not going to help and start trying to handload for their parts guns.

USSR
May 3, 2007, 08:42 AM
If the Army is getting 2750 fps at 50,000 psi why is Remchester not getting about 3100 at 62,000 psi? (Rule of thumb confirmed by Vihtavuori, the increase in velocity is about half the increase in pressure.)

Answer: The Army still goes by crusher gauge readings but since they are not a member of SAAMI do not recognize the CUP terminology and report crusher data in psi.

Exactly. Thanks Jim. I don't know how many times I have seen guys make direct comparisons of the 50,000psi level of 7.62x51 and the 62,000psi level of .308 Win, and come to the erroneous conclusion that the .308 is too powerful to be fired in a 7.62x51 rifle.

Don

Onmilo
May 3, 2007, 09:02 AM
Headspace.
.308 Winchester 1.629" minimum 1.637" maximum
7.62 NATO 1.634" minimum 1.640" maximum
Pressure has nothing to do with the incompatability between the cartridges in standard factory chambered rifles.

A good compromise chamber dimension is 1.635".
The 1.635" dimension will allow the shooter to safely use factory loaded standard pressure .308 or 7.62 with 140 to 168 grain bullets.

The problem comes when guys try to reload .308 dimension cartridges that have been fired in a 7.62 NATO dimension chamber.
Cases stretch excessively and cannot be resized back to original Winchester dimensions.
Cracking and case head seperation occurs in as few as ONE reloading cycle.

If you choose a compromise chamber dimension and wish to reload it is well advised to stick with NATO dimension cartridge cases only and one must discard any and all factory .308 dimension cartridge cases fired in the compromise chamber rifle.

I may go to a 1.633" chamber dimension in the near future if 7.62 NATO continues to climb in price as factory .308 is becoming almost as cost effective to shoot right now.
If the situation again changes I will redimension the chamber of the customers barrels to my compromise dimension at a very nominal charge if they want it done.. We'll see what happens.

Jackal
May 3, 2007, 11:23 AM
Shoot all the 7.62 you want. Your not gonna hurt that Marlin.

USSR
May 3, 2007, 12:03 PM
The problem comes when guys try to reload .308 dimension cartridges that have been fired in a 7.62 NATO dimension chamber.
Cases stretch excessively and cannot be resized back to original Winchester dimensions.

The cartridge dimensions are the same, it is only the chamber dimensions that are slightly different. So, regardless as to whether you are using 7.62x51 brass or .308Win brass, you are resizing them both back to the same cartridge dimensions. Granted, using some brands of commercial brass in an overly large 7.62x51 chamber will result in short case life, but so will using 7.62x51 brass originally fired in a machinegun.

Don

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