I read that the 7.62x51 has a maximum pressure of 50,000 psi while the .308 can get up to 62000 psi and therefore shouldn't be used in a firearm branded for 7.62x51.  Thoughts?

*Edit* The chamber dimensions are different, cases are the same *Edit*.  The rules are the same as 5.56 vs. .223:  You can shoot .308 in a 7.62 chamber, but you shouldn't shoot a 7.62 in a .308 chamber

There are some good articles on the differences between the two with a google search.

FYI, I called a few gun stores to ask the same question, and they said there's no difference, BS.  I called DPMS, and they said you void the warranty if your shooting 7.62 in a .308 chamber, it causes excessive wear.

A reference article:

http://www.smellysmleshooters.net/ammopressure.htm

The Sammi max pressure for 308 is 62K not 86K
From what I understand you can shoot a 7.62 nato round in a modern rifle designed for 308 but I am not 100% on how safe that is.
I just shoot all 308.

You do not want to shoot a 308 round in an older rifle
like a Mosin Nagant.

The 308 has a higher max pressure, true.    Thats the only real difference.   But be careful of units PSI not the same as CUP and it gets confusing easily.   The difference is not enough to worry about.

The dimensions for the rounds are the same.    If you think they are different, then try and buy some 7.62x51 dies.   They dont exist.   308 win is the only cartridge offered.

The only dimensional difference is on the guns, not ammo.  The range of headspace allowed in the chambers.   7.62x51 has a longer headpsace range allowed before its a reject.   Only really old guns, or open bolt machine guns were made to the longer end of the headspace range.   These military gas guns have a max headspace 8 thousands longer than SAMMI max (1.6455" vs 1.638") .   However ammo is made to the shorter end of the headspace  range (1.631"-1.632"), which is exactly with in spec for 308.   In fact, some Nato 7.62 ammo is made with even tighter headspace (1.629-1.630)!

This is much ado about nothing.    308/7.62 are interchangable.    If you find crappy surplus from 1957 and it does not run good in your 308, then get some better ammo!   308 commercial is fine for either chamber.   If you are really paranoid about such things, get some SAMMI headspace gages (1.630 GO, 1.634 NO GO, 1.638 FIELD REJECT) go crazy.

In general, 308win is a tighter chamber than 7.62.   You can shoot either ammo out of either gun, but the 7.62 guns tends to be more forgiving, since its looser.   308 tends to be more accurate since the chamber is tighter.  

ETA:
http://www.303british.com/id36.html
And DPMS will void your warrenty for reloads too, so take what they say with a grain of salt.


SAMMI puts out a list of dangerous combinations:
http://www.saami.org/specifications_and_information/publications/download/SAAMI_ITEM_211-Unsafe_Arms_and_Ammunition_Combinations.pdf
Notice that 7.62x51 is not listed as unsafe for 308.   And then look at .223 and see whats listed...    This makes it clear, the 223/5.56 comparison is incorrect.

You must be talking about a "converted" MN...they're 7.62x54R.

Yeah you are right

The pressure is higher on .308.  It is exactly the opposite as the issue with .223 vs. 5.56.

Your right, it is the chamber, not the casing that has different dimensions.  I still think you should only shoot .308 in a .308 chamber, but both in a 7.62 chamber.

Most def. Cause the Mosin Nagant is chambered for 7.62x54r

You don't want to shoot .308 in a Nagant because it's not chambered to fire that round...

The NATO 7.62x51 round has thicker case walls to allow for a generally looser chamber. And is the lower pressure of the two rounds. So in a firearm chambered in .308 Winchester it would be safe but may cause some feed issues or be hard to chamber and extract if the manufacturer runs to the upper limits of the headspace tolerance. The .308 Winchester round in a firearm chambered in 7.62 NATO is usually safe providing it has a good chamber. Try it in a battle worn full auto chamber and you're looking for trouble. Most of the info out there says you can run either in a .308 chamber but only 7.62 in the NATO chamber. It's the opposite in the 5.56 versus .223 world.

I shoot both types of ammo interchangeably in both chambers. 7.62x51 chambers are looser and will create less pressure than a comercial .308 weapon shooting the same ammo.

The only place I've run into issues is reloading 7.62x51mm brass.  The thicker brass runs higher pressures than comercial .308 brass with the same powder charge.  However, that brass (mixed comercial and surplus) is used for plinking rounds so I generally run mild loads anyway.

ETA: Don't quote me on this, but I seem to remember reading that somewhere along the line the military confused CUP and PSI, and mislabeled 7.62x51's max pressure as 50k PSI when it was actually 50k CUP, which is about the same as .308 win.

No. The opposite is true. You can shoot 7.62x51 in a 308, not the other way around. It is the opposite of the 5.56 vs .223 rounds.

you'd be better off deleting your post

Direct from DPMS: Our .308 barrels are designed to be used with match grade .308 ammo only. You may experience extraction failures if using 7.62 mil surp. For that reason DPMS does not warranty the use of 7.62 in our 308 chamber. Our 7.62 barrels were designed to handle both.

I'll be happy to forward you the email from the Manufacturer who I have to assume is an expert on the subject.  

You'd be better of to go back to 5.56 and .223. At least we know what to shoot in what

They didn't say "Dont do it, you'll shoot your eye out!"   they said, "May experience extraction failures".   So, its ok to do it, but don't be surprised if it some crappy surplus don't run very good.   I expect thats the whole thing in a nutshell.   "Its no big deal, and crappy ammo can be crap."   Surplus ammo is "surplus" for a reason–– its not worth keeping.

And as for "voiding the warranty", I am sure that's because they don't want customers calling:   "I tried to shoot some 7.62 ammo from India in 1973 and it jams my rifle.   I want my money back!"

Brand new Winchester White box 7.62 will run fine in 308.

I suggest you continue shooting 7.62 in a .308 chamber then.

Didn't Winchester simply standardize the then new T65 cartridge? If so, the rifles that were chambered for it then should be safe to shoot it in now. SAAMI says you can interchange them without problem.

Very good article on this discussions - lots of details, and worth the read:

7.62mm vs. .308 Win

I shoot commercial .308 in both my Ishapore Enfield and the FAL I built from a STG 58 parts kit.

The entire "Commercial 308 is not safe in 7.62 military rifles" is total hogwash.

Also all commercial 308 chambered rifles I have messed with shoot military 7.62 just fine.