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I have looked up the difference but seem to find conflicting answers. I understand the head space difference, brass thickness difference and possible loading differences, but is this basically what it boils down to:

"ANY rifle chambered for .308 Win. will fire 7.62 x 51 ammo without a problem. There are instances where problems have arised when trying to use .308 ammo in precision rifles chambered for 7.62, because a slight difference in the headspace"

I want to make sure before I load up on 7.62x51mm.
 

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I have looked up the difference but seem to find conflicting answers. I understand the head space difference, brass thickness difference and possible loading differences, but is this basically what it boils down to:

"ANY rifle chambered for .308 Win. will fire 7.62 x 51 ammo without a problem. There are instances where problems have arised when trying to use .308 ammo in precision rifles chambered for 7.62, because a slight difference in the headspace"

I want to make sure before I load up on 7.62x51mm.
There is a huge amount of information out there on just this question, and there are really three camps of thought based on different information. The three camps are as follows:

1) they are interchangable and go ahead and swap them around
2) it is okay to fire .308 out of a 7.62x51 rifle but not vice versa due to the higher pressure from a 7.62x51 round. In some precision .308 rifles, a 7.62x51 round will not fit due to the 0.005" longer headspace.
3) it is okay to fire 7.62x51 out of a .308 rifle but not vice versa due to the lack of stringent controls on the .308 cases which can result in a failure to extract due to the thinner brass with a shorter headspace used for the .308 both stretching forward and expanding thereby locking itself up in the chamber after firing.

As I said, there is a huge amount of data out there...what it really comes down to is the individual weapon and the rounds used. NATO rounds are held to an extremely strict quality control and therefore you can expect an extremely high level of consistency. The .308 rounds are not held to that same level of stringent control and may vary by manufacturer. A well built .308 rifle should not have issues with the increased pressures from the 7.62x51 rounds, however a high precision rifle may fail to lock forward fully due to the longer head on the 7.62x51 rounds. A weak or poorly made .308 rifle may develop a catostrophic failure due to the increased pressure of the 7.62x51 ammunition. 7.62x51 rifles may fire .308 with no issues (the brass is usually not capable of being reloaded afterwards though). In some 7.62x51 rifles they may fail to cycle or fail to eject due to the case expansion of a .308 round.

--Wintermute
 

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Information is Ammunition
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im sure theres few 'operators' out there that may know the answer to that. I'm sure many SOCCOM guys may know the answer to that. equipment OSP is taught even at basic infantry schools I believe.
 

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American fearmaker
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Think of it like this: Military firearms are deliberately designed rifles to operate with weaker pressures. Civilian rifles operate with higher pressure for different shooting needs. In a war, the military looks for ways to scrimp and save material. This includes the amount of gunpowder in a cartridge. You can take the same amount of material like propellant, bullets and brass for cartridges and the military will make 1,000 rounds out of it. Give a civilian who does super accurate shooting the same exact material and he may need a higher pressure to get the precision out of the round that he's shooting. That's why using the same exact material the civilian shooter will produce 900 cartridges. As a loose/general rule, higher cartridge pressures = a flatter trajectory = better accuracy. For most soldiers in the military, the military is looking for general "combat accuracy." They want decent stuff to be able to hit a target so they're willing to use lower pressure in their cartridges. Civilian shooters are more apt to need "high precision accuracy" for competition shooting. Now, there is one exception to the military rifles. Know what it is? A: Bolt action sniper rifles. With military bolt action rifles, the bolts are re-enforced and made sturdier so that both military cartridges AND high precision accuracy civilian cartridges can be used for shooting needs. So your military bolt action rifles and your civilian bolt action rifles can both shoot just about ANYTHING in .308/7.62 NATO. If you look at some rifles, not all of them, they may have markings which say .308/7.62 NATO or .308 caliber only or 7.62 NATO only. If a rifle says like .308/7.62 NATO that means it is specifically designed to use either or both types of cartridges. Same thing applies to 5.56/.223 rifles. If, however, a rifle has one type of marking, like only having 7.62 NATO, then you probably should stick to using only 7.62 ammo in that rifle. There is a good possibility that very high powered .308 ammunition could damage your rifle. Keep in mind that there is an overlap where rifles can actually use most of the other caliber cartridges. But the extremely low power military cartridges may not work in the rifles labeled .223 or .308. So you might want to chronograph the ammo you are planning to use and figure out where your ammo falls in among the different pressure groups for the cartridges you plan on using. So if you are not at the extreme ends of the pressure factors or at the extreme ends of feet per second travel speed for the bullets, you will probably be okay to shoot either. Keep in mind that if you are using the extremely lower power ammo such low power ammo may cause your rifle to jam a lot more than usual. Lower power ammo may not have just the right minimum amount of pressure needed to operate the semi-automatic version of a higher pressure using civilian rifle. It probably will not damage the rifle but it will or can be awfully frustrating.
 

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So much of that information is incorrect. Go ahead and read this link in order to get a clearer understanding of the differences. I didn't write this page, however, all of the data clearly matches to that in the Lyman reloading manuals as well as to actual case measurements between the two cases.

--Wintermute
 

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Always watching from afar
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Actually in the 5.56 vs .223 Rem. the it is the reverse of 7.62 vs .308.

A .308 can shoot 7.62 but not the other way around.

A 5.56 can shoot .223 but not the other way around.

Hope this helps.
 

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Hmmm.....ok well...some of the info is correct..however much of the newer military Nato ammo is actually very thick ( case wise) for eg. I took out my M-14 Harrington and richards and shot Nato box ammo through it..no probs, however when I shot one round through my Sako .308 rifle I had a hard time extracting it ( Nato ammo 7.62x51) So....do the math and take the prior posts info with mine and figure it out. Yup this is a class now :)
 
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