.308/ 7.62Nato interchangeability

[uwspmgc]

since 7.62x51 is a military cartridge i assume it is used for tactical rifles such as AR's and sniper rifles, and the .308 is better served for hunting purpose. what about vice-versa? can i get AR's and hunting rifles that could handle both?

Disclaimer-
i'm sure this question has been asked a million times a million different ways. in no way do i mean to offend anyone by my ignorence.

 

[375shooter]

since 7.62x51 is a military cartridge i assume it is used for tactical rifles such as AR's and sniper rifles, and the .308 is better served for hunting purpose. what about vice-versa? can i get AR's and hunting rifles that could handle both?

Disclaimer-
i'm sure this question has been asked a million times a million different ways. in no way do i mean to offend anyone by my ignorence.

I believe they are the same but cannot be 100% sure. I have a customized military Mauser rifle made in 1952 with 7.62 stamped on the receiver ring. It's the rifle I carry most often when going after deer. I fire .308 handloads in it.

 

[Casefull]

Do not worry about it...I use them interchangeably. You will find those who go into great detail about all the potential differances but for the average shooter not a big deal.

 

[Z-Michigan]

As a practical matter, most (not all) rifles chambered for one are fine with the other.

Cartridge dimensions are ever so slightly different, but most ammo made for one will fit both. Pressure limit is higher for .308 but most (not all!) 7.62 NATO firearms can safely fire the .308 Win ammo.

 

[powermad]

The military now uses the strain gauge instead of CUP.
Recent measurements for 7.62x51 is 61,150 psi max
SAMMI .308 is 62,000 psi max.
Not enough to worry about pressure wise.

As long as the headspace does not exceed 1.634" .308 will be fine.

 

[General Geoff]

Unless it's an old milsurp rifle or machine gun chambered in 7.62x51 NATO (both of which tend to have loose chambers), they're basically interchangeable. Some autoloading rifle gas systems are designed to work within a certain projectile weight range, owing to pressure curve variations.

 

[madcratebuilder]

As long as the headspace does not exceed 1.634" .308 will be fine.

+1

Head space is the only concern I would have.

 

[uwspmgc]

i figured i can buy the 7.62 in bulk for my AR and use it for target practice in my hunting rifle. of course for hunting purposes i'll use .308.

 

[Palehorseman]

Years ago I bought a five gallon bucket of 7.62 NM brass for 25 bucks, aside from backing off a bit on reloads , I have used it in sporting rifles with good results.

 

[PAPACHUCK]

Any 308 will shoot either, but an older rifle chambered in 7.62x51 should only be shot with 7.62x51.

 

[jonnyc]

"Any 308 will shoot either, but an older rifle chambered in 7.62x51 should only be shot with 7.62x51."

Poppycock.

Factory loads in 7.62x51 and .308 are the same cartridge, and perfectly interchangeable. As stated above, some military chambers might be a bit more generous and some commercial chambers might be a bit more stingy, but they are the same round.

 

[Driftertank]

Somebody needs to sticky one of these threads one of these days, and one for .223/5.56 Seems like every week somebody want to know the difference.

 

[General Geoff]

"Any 308 will shoot either, but an older rifle chambered in 7.62x51 should only be shot with 7.62x51."

Poppycock.

Factory loads in 7.62x51 and .308 are the same cartridge, and perfectly interchangeable. As stated above, some military chambers might be a bit more generous and some commercial chambers might be a bit more stingy, but they are the same round.

Said older 7.62 chambered rifles with loose chambers, should only be shot with 7.62 ammo. 7.62 NATO brass is thicker and sturdier than .308 Winchester brass, and as such can be safely fired in a looser chamber than .308 Winchester.

 

[Balrog]

Cartridge dimensions are ever so slightly different, but most ammo made for one will fit both. Pressure limit is higher for .308 but most (not all!) 7.62 NATO firearms can safely fire the .308 Win ammo.

The cartridge dimensions (ie, external dimension) are the same. If there were different dimensions, you would not be able to load them both with the same reloading dies.

The internal case capacity of 7.62 brass may be less than 308 brass because 7.62 brass may be thicker.

 

[USSR]

The cartridge dimensions (ie, external dimension) are the same. If there were different dimensions, you would not be able to load them both with the same reloading dies.

The internal case capacity of 7.62 brass may be less than 308 brass because 7.62 brass may be thicker.

Yep. Worse case scenario, commercial .308 ammo shot in a "generous" 7.62x51 chamber will result in reduced case life. Winchester and Hornady Match .308 brass are quite a bit lighter than military 7.62x51 brass, and charge weights to generate similar velocity will be 1.0 - 2.0 grains more than in LC M118 Match brass.

Don

 

[Kwanger]

Here:

http://www.303british.com/id36.html

Decent explanation, if a little on the scaremongering side (personally, I've used both in a 7.62 chambered rifle, no probs so far - but who am I to know)...but will help you understand the differences.

 

[W.E.G.]

Its up to the owner of the gun to figure out whether "its OK" or not.

I've never heard of .308 causing any sort of catastrophic failure in 7.62 rifles. While it may be true that .308 has a higher SAAMI-spec rating than 7.62 NATO, that certainly does not mean all commecial .308 is loaded to maximum SAAMI spec.

I have heard of commercial .308 (Winchester white box IIRC) not reliably extracting from some CETME and/or HK-type (delayed-blowback) rifles. Some reports indicated the delayed-blowback guns literally ripped the case heads. Its not clear to me whether the reports were head-separations, or the extractor ripping through the rim before the case would let go of the chamber. If indeed the .308 had higher pressure, it would be my opinion that the "brass not letting go" is a likely cause. Moreover, if you ever got your hands on Pakistani ammo designed especially for the fluted 7.62 chamber, you will notice a waxy coating on the ammo. This is another let-go-of-the-chamber feature you won't find in Remington .308 ammo bought at Dick's Sporting Goods.

Similarly, I have heard of 7.62 ammo not reliably extracting from DPMS LR-308 type rifles. Whether this is a function of too little gas pressure from the foreign-made 7.62 milsurp ammo, or is a function of external dimensions of the ammo, I do not know.

I measured various milsurp 7.62 ammo. One batch of Malaysian linked machine-gun ammo significantly exceeded the conventional .308 spec of 1.630" from the base of the cartridge to the datum-line on the shoulder. The only .308 I had on hand at the time of my measurements was a box of Federal Gold Medal .308. The Gold Medal measured within about 0.002" of the measurements I was getting for several of the various milsurp 7.62. I wrote a "report" of sorts on these measurements. You can read my report at http://www.falfiles.com/forums/showthread.php?postid=2160133#post2160133

One might speculate that third-world machine-gun ammo tends to be of greater "headspace" dimension (longer from base to shoulder datum-line) as the guns used by those countries are more worn-out than brand-new American guns. So much for a "standard" NATO spec.

Here's a quick summary of the "report."

 

[Candiru]

I did a writeup on the difference: link

 

[bigalexe]

Speaking strictly about diameter using the conversion of 25.4mm = 1 inch

7.62mm = 0.300"
0.308" = 7.8232mm

I know there is availability of .308 caliber AR-Pattern rifles under the AR-10 or SR-25 names. If I can afford it that will actually be my first AR Rifle is the .308 because if I am spending that much money on a gun I want earthquakes when it goes off.

 

[uwspmgc]

an old timer at the range told me .308 has slower burning powder causing higher chamber pressures than a 7.62. because of this, using .308 in a semi-auto rifle could cause it to "run hard", whatever that means. i guess my next question is- is there a difference in external ballistics between the two?

 

[USSR]

7.62mm = 0.300"
0.308" = 7.8232mm

You do understand that 7.62mm refers to bore diameter, while .308 refers to groove diameter (.004" depth on each side of the bore)?

Don