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762x51





MP15Reloader

Obsessed Member
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#2
What is the exact difference between .308 Win and 762 nato. My rifle says .308 Win only.
Think of it like the 556 223 thing.. 223 is safe to fire in a 556 chamber but 556 is not safe to fire in a 223 chamber due to higher pressure.

If i remember correctly 762 snd 308 is reversed. 308 chambers can fire both 762 and 308 but 762 chambers should only fire 762. Im iffy on this so double check but not sure if its a pressure, headspace, etc issue. Your 308 chamber should handle 762 ammo fine just dont expect stellar accuracy and if you reload, consider 7.62 brass has thicker walls than commercial 308.
 

Mooman76

Obsessed Member
#3
I heard this too but don't know it for a fact because you hear allot of crap on the internet. Do some research on the pressures.
 
#4
What kind of rifle is it, and what is it going to be used for?


would make different recommendations for a high end bolt rifle used for precision shooting vs a semiautomatic that is used for plinking.
 

NYECOGunsmith

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#5
There are differences between the commercial .308 Winchester round and the military /NATO round called the 7.62x51mm, and they can be a problem in several areas.

While the physical outside dimensions of the cartridges are virtually identical, the insides, and more importantly, the chamber dimensions ARE NOT the same.

For starters, lets take a look at the head space gauges for each cartridge.

308 Winchester (SAAMI) Gauges

GO - 1.6300"
NOGO - 1.6340"
FIELD - 1.6380"

7.62x51mm military Gauges
GO - 1.6350"
NOGO - 1.6405"
FIELD - 1.6455"


Notice the Military round has more "generous" lengths on all three gauges.

So the problem occurs when firing commercial .308 Winchester ammunition in a 7.62x51mm chamber, the greater length allows the case to stretch a good bit.....and since commercial .308 ammunition uses brass cases with a thinner case wall, and since the .308 has a maximum SAAMI pressure rating of 62,000 PSI versus the 7.62x51mm's max rating of 58,000 PSI, sooner or later you are going to have a ruptured case on your hands.

Also, the 7.62 is proofed at 67,000 PSI , where as the .308 is proof load tested at between 83,000 and 89,000 PSI, depending on what country is doing the proofing.


In some rifles this will just be an unpleasant experience that results in having to dig the pieces of brass out of the chamber, and hopefully no gas particles, brass particles, etc. made it out of confinement and into the shooter's face, hands, etc.

But with some weaker actions, such as the models 93 or 95 Mauser, converted and chambered for 7.62x51 NATO, firing a commercial .308 Winchester load in it with that long head space and higher pressure could be a real disaster.

If a rifle is chambered for the .308 Winchester and is in good condition (no reason NOT to fire it with factory .308 ammunition I mean) it will handle the lower pressure military round without a problem, pressure wise.

I should note that there is another 7.62x51 round out there, the 7.62x51 CETME round, made in Spain, which is a totally different cartridge using a much lower chamber pressure and a 113 grain bullet at only 2400 FPS.

Also, if anyone has any 7.62x51 ammo marked "CBC 7.62 75" made by CBC of Brazil, don't shoot it! This stuff was a manufacturing mistake, and has blown up a huge number of guns since it escaped the factory in 1975, lots of it tested had an average CUP (Copper Units of Pressure) rating of over 130,000! There isn't commercially made rifle in existence that will handle that, it even blew up an number of 2" diameter test barrels.
 

Kinoons

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2019 Supporter
#7
I think you missed the point of NYCOs post. Yes there is a difference between .308 winchester and 7.62x51 NATO. However our commercial ammo is likely loaded at a higher pressure than the NATO military stuff.

From his post

If a rifle is chambered for the .308 Winchester and is in good condition (no reason NOT to fire it with factory .308 ammunition I mean) it will handle the lower pressure military round without a problem, pressure wise.
If you have a .308 winchester rifle feel free to buy up all the $0.50 a shot military surplus 7.62x51 you can get your hands on.