hey guys, i'm sure this question has been asked a million times already but i seem to be confused in the area.  i'm thinking about getting a .308 gun at some point and just want to know the difference between the two cartridges. as i understand it, if i get a gun chambered in .308 win, i can use mil surp 7.62 nato rounds in the gun, correct? i also understand (correct me if i'm wrong) that you can not use .308 in a mil spec 7.62 nato chamber.  so as long as i get a .308 chmaber i'm good to shoot both (7.62 for plinking and .308 for more serious target and hunting)? thanks for the clarification

You will hear that the 7.62 and .308 are different and that the .308 is made more powerful so it will blow up NATO guns.
The problem is you will not find any proof that the rounds are different because the pressures are always charted in different format. I have NEVER heard of anyone actually having a problem shooting .308 from a FAL or G3 or any rifle made for 7.62 NATO.
The only problems I have heard of are ones anticipated by someone who looked up charts on the two rounds and misunderstood the pressures because the were not in the same format. They then wrote up an article that has turned into a ''guess what I know that you don't'' type of thing and now alot of people believe the rounds are different.
I consider .308 and 7.62 NATO to be interchangable and like I said, I have NEVER heard of anyone having a problem using .308 in 7.62 marked rifles.

What's the Difference between .308 Winchester & 7.62x51mm NATO?

Simple answer, the NATO spec chamber can be longer than the SAAMI spec for the 308 chamber.

7.62 and .308 differences summed up:

7.62 has a longer permissible headspace for reliability in full auto weapons.
7.62 has thicker brass
7.62 is loaded to lower pressure (compare CIP specs to NATO specs since they use the same measurement standard)

Because the 7.62 potentially has a long chamber, the brass is made thicker and pressure kept lower to keep from rupturing cases.  Firing a .308 round with higher pressure and thinner brass in a chamber with excess headspace (by .308 standards) is asking to blow up a case.  Might not hurt the rifle but will probably scare the crap out of the shooter when he gets a face full of hot gas.

If a rifle marked 7.62 has the chamber checked and it falls within .308 headspace dimensions, firing .308 in it should be OK.  Be cognizant of gas volume and pressure with piston operated rifles as too much of either can damage the operating system.

This.  Over the years I have used milsurp and commercial .308/7.62 ammo intechangeably in my rifles.  From a Savage 99 lever action rifle for deer hunting in the 1970's to three PTR91 semi-auto delayed-roller block rifles today.  The 91's see a couple of different European surplus types as well as Federal American Eagle commercial.



The only effect I have ever seen of a long military chamber is that over repeated firings brass can stretch.  If you reload that brass a number of times you might eventually get a head separatiion.  A broken brass extractor would come in handy at that time.  I was in the Army when I owned the Savage 99.  Friends often brought me spent brass from the machine gun ranges.  Those M60's really gave the 7.62 rounds a good stretch, but I happily reloaded it all.

The potential for a long chamber varies as mentioned in the link I provided. With ammo I reload for my AR 10 that gives no abnormal stretching after multiple firing and reloading in the AR10 will be on the verge of a head separation when fired in my M14. One shot in the M14 and the brass is not reloadable. Same ammo is OK in my 1919 but there I can set the head space on the barrel as I like. These loads are using unfired pulled down US 7.62 brass that I resize to my AR10 chamber.

Nothing wrong with a 7.62 NATO chamber but if it's on the long side of the NATO spec range don't expect to be reloading your brass.

thanks for all the replies guys. so looks like i can use the 2 rounds pretty much interchangeably in whatever rifle i get.  i'll probably end up with a bolt .308 because its going to be a hunting gun only and don't want to spend the money on an ar-10 if i'm not going to be plinking with it (.308 is too expensive for me to shoot for fun).

The pressure difference between the two rounds is insignificant, the real problem is commercial ammunition has thinner cases that were not designed to shoot in military chambers BUT we do it all the time anyway and this why you see more case head separations on commercial cases fired in military chambers.

The M118 special long range round is loaded to 52,000 CUP (all other U.S. 7.62mm are 50,000 CUP) which would be equal to the pressure levels of commercial ammunition, this means actually there is no pressure difference between the .308 and 7.62 NATO for the M118 cartridge.

The pressure difference between the 308 Winchester and the 7.62x51mm NATO is less than 2,000 PSI which is statistically insignificant. The same pressure variation may be achieved by firing any rifle on a hot day and on a cold day or by changing brands of primers.