Hi all, I tried looking for this and am sure it has been discussed but I cant get a solid answer on this. I have an MR.308 and want to know if i can cycle 7.62 Nato rounds through it. The information I have is that the .762 will work in the .308 but is not recommended the other way around because of pressure (but supposedly pressure is measured differently and still works). My Ar-15 is barrel stamped for .556 and .223 but the MR.308 is only stamped for the .308. Would be nice to get someone view who has had a practical experience with it. Cheers
.308-.762 Interchangeable
- Thread starter Guy_Lizard
- Start date
Stolen from google :
Although the outer case dimensions and bullet dia. are technically the same in both rds. there are a few differences. For one the pressure differences between the two rds. are different the x51 NATO MAX proof pressure is 50K PSI while the 308 is 62K,it's perfectly fine to shoot good quality X51 NATO ammo in any 308 Win. chamber rifle. You CAN encounter problems going the other way, however. A commercial .308 Win round can exceed the max rated pressure for the 7.62x51. So, you should avoid putting full-power .308 Win rounds into military surplus rifles or one that has been designed specifically for the 7.62 x 51 NATO cartridge.
The chambers are totally different and so is the commercial 308 brass vs. the X51 NATO brass,308 commercial brass is thinner and when fired in a X51 chambered rifle overly expands if your a reloader repeated full length resizing of 308 commercial brass and firing it in a X51 chamber will cause case head separation and short brass life unless you neck size only which is fine in bolt guns but not recommended with semi-autos due to feed and chambering issues that can arise.
TLDR: best not to swap them out, but if you want to you can.
Although the outer case dimensions and bullet dia. are technically the same in both rds. there are a few differences. For one the pressure differences between the two rds. are different the x51 NATO MAX proof pressure is 50K PSI while the 308 is 62K,it's perfectly fine to shoot good quality X51 NATO ammo in any 308 Win. chamber rifle. You CAN encounter problems going the other way, however. A commercial .308 Win round can exceed the max rated pressure for the 7.62x51. So, you should avoid putting full-power .308 Win rounds into military surplus rifles or one that has been designed specifically for the 7.62 x 51 NATO cartridge.
The chambers are totally different and so is the commercial 308 brass vs. the X51 NATO brass,308 commercial brass is thinner and when fired in a X51 chambered rifle overly expands if your a reloader repeated full length resizing of 308 commercial brass and firing it in a X51 chamber will cause case head separation and short brass life unless you neck size only which is fine in bolt guns but not recommended with semi-autos due to feed and chambering issues that can arise.
TLDR: best not to swap them out, but if you want to you can.
Steve Janes
CGN frequent flyer
- Location
- Calgary/Ontario
Great article on the differences between .308 and 7.62 NATO
http://www.303british.com/id36.html
Do you have a military surplus rifle chambered in 7.62 x 51mm? If so, you probably bought it to get a "308 Winchester" at a really low price. Well, you messed up. It's like looking at a rabbit and a hare. They're close, but each is distinctive, and you have to understand what you're looking at.
Early in my military career, I worked on the FNC1 rifle (7.62 NATO). For someone that had only handled civilian shotguns and rifles, this was going to be a real treat! It was only natural that curiosity would generate questions and comparisons about what I thought was the same cartridge - 308 Winchester and the 7.62x51mm NATO.
FNFAL.jpg
One of my personal rifles was a Midland 2100 chambered for 308 Winchester. It was made in England by a small company - Midland Rifle Co - but owned by Parker Hale. Since there was a lot of military 7.62x51mm available, I shot them from my 2100 from time to time. There was never a problem chambering or firing the military stuff. It was a pleasant diversion over the long (read boring) periods spent at the range for base small arms qualifications.
Around this time, I discovered that shooting reloaded cases fired from an FN was virtually impossible. They didn't want to chamber. My frustration led me to ask an older armourer what was wrong. In a nutshell, he told me that they probably didn't fit because they stretched. I was using a Lee Loader in 308 Winchester and didn't know that they only resized the neck, leaving the rest of the case untouched. The shoulders were blown forward on initial firing, so the case was simply too long to fit my rifle's chamber! Hmmm...
I tried the gauges from work in my own rifle and was surprised to discover that none of them would fit! The corporal brought a set in from home and explained the difference. Here's what I discovered.
308 Winchester (SAAMI) Gauges
GO - 1.6300"
NOGO - 1.6340"
FIELD - 1.6380"
Shop (Military) Gauges
GO - 1.6350"
NOGO - 1.6405"
FIELD - 1.6455"
The gauge sets were different too! What gives? He told me that the dimensions of the two new and unfired cartridges were basically the same. The difference lay in two areas - chamber size and cartridge makeup.
CHAMBER SIZE
Look at the picture below. The top chamber represents a military rifle, the bottom one a commercial sporter. With many military rifles, their chambers can be significantly longer than, say, a Remington 700. Note that the military chamber would fail a NO GO check, but pass a FIELD check using the proper shop (military) gauges.
There is a .013" difference in chamber length however, between these two "Safe & Serviceable" rifles!
rimless2.JPG
The dotted line represents the point on the shoulder where the cartridge would headspace
There will be distinct differences between chambers of military rifles based on:
Type - Ishapore, Garand, FN etc.
Amount of Use
Condition at Time of Sale
Just by looking at the dimensions, you can see that using SAAMI gauges is bound to reveal "problems".
CARTRIDGE MAKEUP
I said at the beginning that these two cartridges were basically the same, dimensionally. While they may share similar external measurements, there is one major difference that you can't see - case wall thickness.
thickness.JPG
Military brass is thicker. It needs to be. It was made to function and stretch in a wide variety of firearm chambers. Don't forget that the condition of spent brass is of no importance to the service. Like 99% of military brass, it won't be reused.
Where does that leave you? Follow this rule and you won't have any problems.
DON'T USE YOUR RIFLE IF IT FAILS THE SAAMI FIELD CHECK!!
Why not? Right away you know that the chamber is measuring more than 1.6380" (SAAMI FIELD) - possibly more. Commercial 308 ammunition may stretch by 0.008" when fired! Possibly more. It may even rupture! You must get the headspace corrected to bring it in line with SAAMI specs. Hey, it's for your own safety!
Based on this rule, find your situation below.
__
I DON'T RELOAD AND USE ONLY MILSURP AMMUNITION.
You shouldn't have any problems.
I DON'T RELOAD BUT WANT TO USE COMMERCIAL AMMUNITION.
There is a potential problem with brass integrity. Commercial cases are NOT as thick as their military cousins. There is less brass, so if you use them in an original, unmeasured military chamber, there may not be sufficient material to stretch and fill the chamber without rupturing. That's bad!!
I RELOAD.
You know that commercial brass is thinner. An easy way to see this is to weigh a fired case of each type. You'll see that the commercial case is lighter. There may not be enough brass left - after lengthening - for any decent case life. You will only aggravate the situation by full length resizing (it weakens the case by overworking the brass), loading at or near maximum or both.
__
If you own a milsurp bolt gun like an Ishapore 2A or 2A1, consider neck sizing the brass for better case life, fit and accuracy.
SOME FINAL THOUGHTS
Military ammunition is loaded to maximum average pressure 50,000 CUP (approximately 58,000 PSI using the modern piezo transducer method of measurement). This standard is used to ensure better consistency round to round. It is proofed at 67,000PSI. The ammunition can then be used in a wide variety of firearms with no ill effects.
Look for the NATO design mark.
NATODesignMark.jpg
NATO mark found on the outside of ammunition containers and the bottom of each case rim.
Commercial ammunition has a SAAMI/ANSI maximum pressure of 62,000PSI. While not every manufacturer may load it to this level, this is the industry established maximum. This is also measured using the piezo transducer method. The proof cartridge pressure is 83,000 to 89,000 PSI. Note the differences between the military test and operational standard vs the commercial one.
The worst case scenario for shooters of 7.62 NATO rifles is as follows: Using a commercially made, maximum pressure cartridge with long headspace, fired from a weak action (ex. converted 93/95 Mausers).
The weaker action is a possible final piece of the 308 vs 7.62 NATO puzzle.
Perhaps no single element will cause your rifle to fail. Maybe you've used your rifle for a while with no ill effects. Usually a rifle will take some abuse before failing. Like a lot of things in life, Murphy's Law - If something can go wrong, it will - could very well catch up with you.
Personally, I don't like the odds.
http://www.303british.com/id36.html
Do you have a military surplus rifle chambered in 7.62 x 51mm? If so, you probably bought it to get a "308 Winchester" at a really low price. Well, you messed up. It's like looking at a rabbit and a hare. They're close, but each is distinctive, and you have to understand what you're looking at.
Early in my military career, I worked on the FNC1 rifle (7.62 NATO). For someone that had only handled civilian shotguns and rifles, this was going to be a real treat! It was only natural that curiosity would generate questions and comparisons about what I thought was the same cartridge - 308 Winchester and the 7.62x51mm NATO.
FNFAL.jpg
One of my personal rifles was a Midland 2100 chambered for 308 Winchester. It was made in England by a small company - Midland Rifle Co - but owned by Parker Hale. Since there was a lot of military 7.62x51mm available, I shot them from my 2100 from time to time. There was never a problem chambering or firing the military stuff. It was a pleasant diversion over the long (read boring) periods spent at the range for base small arms qualifications.
Around this time, I discovered that shooting reloaded cases fired from an FN was virtually impossible. They didn't want to chamber. My frustration led me to ask an older armourer what was wrong. In a nutshell, he told me that they probably didn't fit because they stretched. I was using a Lee Loader in 308 Winchester and didn't know that they only resized the neck, leaving the rest of the case untouched. The shoulders were blown forward on initial firing, so the case was simply too long to fit my rifle's chamber! Hmmm...
I tried the gauges from work in my own rifle and was surprised to discover that none of them would fit! The corporal brought a set in from home and explained the difference. Here's what I discovered.
308 Winchester (SAAMI) Gauges
GO - 1.6300"
NOGO - 1.6340"
FIELD - 1.6380"
Shop (Military) Gauges
GO - 1.6350"
NOGO - 1.6405"
FIELD - 1.6455"
The gauge sets were different too! What gives? He told me that the dimensions of the two new and unfired cartridges were basically the same. The difference lay in two areas - chamber size and cartridge makeup.
CHAMBER SIZE
Look at the picture below. The top chamber represents a military rifle, the bottom one a commercial sporter. With many military rifles, their chambers can be significantly longer than, say, a Remington 700. Note that the military chamber would fail a NO GO check, but pass a FIELD check using the proper shop (military) gauges.
There is a .013" difference in chamber length however, between these two "Safe & Serviceable" rifles!
rimless2.JPG
The dotted line represents the point on the shoulder where the cartridge would headspace
There will be distinct differences between chambers of military rifles based on:
Type - Ishapore, Garand, FN etc.
Amount of Use
Condition at Time of Sale
Just by looking at the dimensions, you can see that using SAAMI gauges is bound to reveal "problems".
CARTRIDGE MAKEUP
I said at the beginning that these two cartridges were basically the same, dimensionally. While they may share similar external measurements, there is one major difference that you can't see - case wall thickness.
thickness.JPG
Military brass is thicker. It needs to be. It was made to function and stretch in a wide variety of firearm chambers. Don't forget that the condition of spent brass is of no importance to the service. Like 99% of military brass, it won't be reused.
Where does that leave you? Follow this rule and you won't have any problems.
DON'T USE YOUR RIFLE IF IT FAILS THE SAAMI FIELD CHECK!!
Why not? Right away you know that the chamber is measuring more than 1.6380" (SAAMI FIELD) - possibly more. Commercial 308 ammunition may stretch by 0.008" when fired! Possibly more. It may even rupture! You must get the headspace corrected to bring it in line with SAAMI specs. Hey, it's for your own safety!
Based on this rule, find your situation below.
__
I DON'T RELOAD AND USE ONLY MILSURP AMMUNITION.
You shouldn't have any problems.
I DON'T RELOAD BUT WANT TO USE COMMERCIAL AMMUNITION.
There is a potential problem with brass integrity. Commercial cases are NOT as thick as their military cousins. There is less brass, so if you use them in an original, unmeasured military chamber, there may not be sufficient material to stretch and fill the chamber without rupturing. That's bad!!
I RELOAD.
You know that commercial brass is thinner. An easy way to see this is to weigh a fired case of each type. You'll see that the commercial case is lighter. There may not be enough brass left - after lengthening - for any decent case life. You will only aggravate the situation by full length resizing (it weakens the case by overworking the brass), loading at or near maximum or both.
__
If you own a milsurp bolt gun like an Ishapore 2A or 2A1, consider neck sizing the brass for better case life, fit and accuracy.
SOME FINAL THOUGHTS
Military ammunition is loaded to maximum average pressure 50,000 CUP (approximately 58,000 PSI using the modern piezo transducer method of measurement). This standard is used to ensure better consistency round to round. It is proofed at 67,000PSI. The ammunition can then be used in a wide variety of firearms with no ill effects.
Look for the NATO design mark.
NATODesignMark.jpg
NATO mark found on the outside of ammunition containers and the bottom of each case rim.
Commercial ammunition has a SAAMI/ANSI maximum pressure of 62,000PSI. While not every manufacturer may load it to this level, this is the industry established maximum. This is also measured using the piezo transducer method. The proof cartridge pressure is 83,000 to 89,000 PSI. Note the differences between the military test and operational standard vs the commercial one.
The worst case scenario for shooters of 7.62 NATO rifles is as follows: Using a commercially made, maximum pressure cartridge with long headspace, fired from a weak action (ex. converted 93/95 Mausers).
The weaker action is a possible final piece of the 308 vs 7.62 NATO puzzle.
Perhaps no single element will cause your rifle to fail. Maybe you've used your rifle for a while with no ill effects. Usually a rifle will take some abuse before failing. Like a lot of things in life, Murphy's Law - If something can go wrong, it will - could very well catch up with you.
Personally, I don't like the odds.
- Location
- Georgetown Ontario
Here we go again!
A whole generation of shooters haven't been wiped out from shooting 7.62 x 51, until the Internet came along, do a search on Google you will find thousands of people talking about it and yet you will not find one single first hand account of a blown up chamber.
come to think of it perhaps none of them survived to tell about it.
come to think of it perhaps none of them survived to tell about it.
The case dimensions of 308 and 7.62 are about the same. the max pressure of the two are about the same.
I have pressure tested a lot of both flavours and pressures are typically around 55,000 psi in both, but I have seen some lots of both 7.62 and 308 running around 60,000 psi.
The ammo is interchangeable.
However, the chambers of some 7.62 rifles are large and deep. This is hard on the brass and the 7.62 heavier brass is better suited to large chambers. Firing factory 308 in a 7.62 will work fine. Multiple reloads of full power with 308 brass could be an issue, especially if you are setting the should back all the way each time.
I have pressure tested a lot of both flavours and pressures are typically around 55,000 psi in both, but I have seen some lots of both 7.62 and 308 running around 60,000 psi.
The ammo is interchangeable.
However, the chambers of some 7.62 rifles are large and deep. This is hard on the brass and the 7.62 heavier brass is better suited to large chambers. Firing factory 308 in a 7.62 will work fine. Multiple reloads of full power with 308 brass could be an issue, especially if you are setting the should back all the way each time.
You won't find Nato 7.62x51 loaded with as high of pressures, as heavy as bullets and as thin of brass as you can find in some 308. Therein lies the danger. You can shoot 7.62 nato in your 308, but you need to consider which 308 you shoot in a 7.62 nato rifle.
Pretty much any current 7.62x51 gun is designed to shoot M993 AP, that has a pressure much higher than .308 SAAMI spec.
I've never seen an issue with any Mil gun and .308 -- other than a lot of .308 older match ammo is softer brass made for bolt guns, and will spit primers if shot suppressed in a gas gun.
I've never seen an issue with any Mil gun and .308 -- other than a lot of .308 older match ammo is softer brass made for bolt guns, and will spit primers if shot suppressed in a gas gun.
Heavy bullets #### up more M1A1/M14's than anything -- they where designed for M80 ball primarily - M118LR beats them up.
Piston guns are much more ammo sensitive than DI guns.
They are safe to shoot .308 for the most part -- its just the carrier velocity when using heavier ammo clobbers them.
Piston guns are much more ammo sensitive than DI guns.
They are safe to shoot .308 for the most part -- its just the carrier velocity when using heavier ammo clobbers them.
Thanks for all the feed back guys. I finally did receive a reply to my inquiry from H&K direct:
Q:Hello from Canada, can I get a firm answer if I can chamber .762 Nato in my MR.308. Thank you and great job.
A: first of all thank you for your email and thank you for your interest in Heckler and Koch
products.
There is no problem at all to use ammunition in caliber 7,62 x 51 NATO or caliber
.308 Winchester. Please check the magazine, you will find the caliber on every
magazine as well.
I hope this will answer your question.
If you have further question, just let us know.
Best regards
A. Schray
Alexander Schray
After-Sales-Service QS
HECKLER & KOCH GMBH, Heckler & Koch-Strasse 1, 78727 Oberndorf a.N.
Geschäftsleitung: Niels Ihloff, Martin Lemperle
Handelsregister: Amtsgericht Stuttgart HRB 481250, USt-IdNr. DE232899163
Q:Hello from Canada, can I get a firm answer if I can chamber .762 Nato in my MR.308. Thank you and great job.
A: first of all thank you for your email and thank you for your interest in Heckler and Koch
products.
There is no problem at all to use ammunition in caliber 7,62 x 51 NATO or caliber
.308 Winchester. Please check the magazine, you will find the caliber on every
magazine as well.
I hope this will answer your question.
If you have further question, just let us know.
Best regards
A. Schray
Alexander Schray
After-Sales-Service QS
HECKLER & KOCH GMBH, Heckler & Koch-Strasse 1, 78727 Oberndorf a.N.
Geschäftsleitung: Niels Ihloff, Martin Lemperle
Handelsregister: Amtsgericht Stuttgart HRB 481250, USt-IdNr. DE232899163
