Can I safely shoot .308 in a 7.62 K98?

Mr. Buttons

Mr. Buttons

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Hi all, I am wondering if it is safe to shoot .308 Win commercial ammo in an Israeli converted 7.62 K98?

From what little I know of the subject, while .308 Winchester is very similiar (but not identical) to 7.62 Nato in size it is also loaded commercially to much higher pressures.

So, with this in mind is it generally accepted as being safe to fire .308 Win commercial ammo in a 7.62 K98?

Thanks and please excuse my ignorance :)
 
:confused:well if it isnt kosher
i been shooting it 20 + years in the ones i own ........
the round is the same ( close enough military use 1 name hunters the other )
only worry is reloading since army brass is slightly different inside dimensions ??
 
naugler said:
Hi all, I am wondering if it is safe to shoot .308 Win commercial ammo in an Israeli converted 7.62 K98?

From what little I know of the subject, while .308 Winchester is very similiar (but not identical) to 7.62 Nato in size it is also loaded commercially to much higher pressures.

So, with this in mind is it generally accepted as being safe to fire .308 Win commercial ammo in a 7.62 K98?

Thanks and please excuse my ignorance :)
Click to expand...

I have shot 180,150 125,130 grain bullets in my 7.62,after firing I neck size so the brass is an exact match to my rifle.
I have heard that some of the military stuff is actually loaded hotter than commercial 308. I have had many, many k98 Mausers in 7.62x51 and shot every .308 diameter bullet weight out of them without a hitch.
Fire away...........:sniper:
 
308 is loaded to SAAMI specs. When Winchester designed the cartridge, they modeled it on the military caliber. Dimensions are about the same. There are some differences:

Military ammo is loaded to specifications that include things like a min and max pressure at a pressure port down the barrel. SAAMI is loaded only to a spec of max chamber pressure.
Military ammo has a spec relating to muzzle flash and smoke. Not a concern to SAAMI.

But you are concerned with pressure and dimensions. The dimensions are close enough to be interchangeable. Pressure limits are the same.

Way back when, pressures were measured using lead and copper crushers in pressure barrels. A hole in the side of the case allowed a piston to move and compress a short piece of copper or lead cylinder. (About a quarter inch in diameter and about a half inch long, as I recall. About the same size as a 38 waddcutter bullet. After firing, the slug was measured with a caliper and the amount it shortened was converted to pressure, using a table. The units of pressure were called CUP (Copper Units of Pressure) and LUP (Lead Units of Pressure).

I conducted thousands of such test shots. It took time to do each one. A real pain. Then the piezoelectric transducer method of testing was introduced. A transducer changed voltage on an oscilloscope and gave instantaneous pressure readings.

For reasons unknown to me, the location of the transducer in the chamber was at a different place than the crusher port would be. For this reason the pressure tables for each test method are different, although the effective limits are the same.

That is, if a round is too hot, it would be too hot with both test methods, although the numbers quoted would be different. Think of speeding. If you are going too fast, it does not matter if your car speedo is in mph or kph.

Of course, with speed, you can multiply by .62 and convert one to the other. Not so CUP and pzeo PSI. Not only are the test locations different, and the units different, but the test locations vary from caliber to caliber.

Why all this history, you ask? Because when 7.62x51 was developed we were using copper crusher pressure guns. The max pressure was/is in the order of 55,000 CUP. But, and here is the whole cause of the confusion, in those days the tables generated CUP units of pressure, and we all referred to the units as PSI, because, so far as we knew, that was what the pressure was.

When the pizeo transducers came into vogue, the civilian world was careful to refer to the old system as CUP and the new system as PSI, so as to avoid confusion as to what was being referred to. For a long time both systems were being used. Maybe someone is still using CUP or LUP equipment. I have not seen one since 1965.

But the military was not concerned about confusion of two pressure systems, because when they wrote their specs, there was only one system - CUP. So they said the max pressure was 55,000 PSI, but they measured with the CUP system.

When the 308 was developed, SAAMI said the max pressure was 55,000 CUP or 60,000 psi. Same pressures- measured two different ways.

The pressure limits quoted above are simplified. An actual test is a 20 round sample. There is a max single round limit for the test and a maximum average pressure for the test. Going by memory, the limits are in the order of about 63,000 psi for a single round and max average for the 20 of about 60,000 psi.

These pressure look high. Most lots of commercial ammo are deliberately loaded to a maximum average pressure of around 57,000 psi.

Military ammo is loaded to very similar limits, but because military documentation will mention a limit of 55,000 psi, the myth has developed that 308 is hotter than military. Not so. When the military say 55,000 "PSI" they really mean 55,000 "CUP".

I have tested hundreds of different lots of both 7.62 and 308 ammo. Almost all of it ran in the range of 55,000 psi to 59,000. I saw no evidence that one flavour is hotter than the other.

Military brass usually has a higher web (the solid section of the base). This forms the solid plug to seal the breach. If a rifle had a shallow chamber, allowing the case head to protrude a bit too much, a high base would seal the breach whereas a low base could blow. Some military automatic have feed ramps that relieve part of the chamber edge, creating a potential for a case to blow.

In general, such rifles are best shot with military cases. Not because pressures are lower (they aren’t) but because the web is thicker.

One rifle that comes to mind is the M14 tuned by one of the marksmanship units. It was the Army Unit, I think, but maybe a different one. They took so much metal off the feed ramp that the rifle would be dangerous with some kinds of brass.

I had occasion to examine a case involving a blown case head. The shooter was not seriously injured, but it could have been worse. Turns out the military 7.62x51 cases he was using (Santa Barbara) had a very, very low web and his rifle had a shallow chamber. As he said "I never had a problem before!"

An article in the NRA magazine The Rifleman last year made a passing reference to the fact that military ammo is the same as SAAMI, but looks different because of the old pressure system. I meant to clip.

I cleaned out my file cabinet a few years ago and threw out a lot of stuff that had been of interest to me. Never occurred to me that anyone else might be.

By the way, the CIP (European standard) is also quoted in psi, but their psi is different because they use different transducers. I have heard, but cannot confirm, that their limits are actually different in real terms for some calibers.

The strength of my convictions does not make me right. Here is where I am coming from.

In the RCAF I was an Armament Officer. I was responsible for small arms and ammo, and the bigger stuff, including rockets, guided missiles, homing torpedoes, bombs and depth charges. We used TNT, C4, RDX and nuclear. Weapons were#4, C#7, Sten, Sterling, FNC1, BHP and Bren. I got to play with them all (except the nuclear stuff). Our paperwork weighed more than a bomb load and I read most of it.

After the RCAF I went to work in the R & D labs of the CIL ammunition division. There I conducted testing of R & D projects, with pressure testing a common test.

I have been hand loading since 1963 and have been the technical director of a small ammo company making specialized ammo for the military and police forces.

In conclusion, shoot 308 in your 7.62x51.
 
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Quote: "So that would apply to converted Garands as well? What about a 7.62 Enfield?"

As I mentioned in my post above, one of the specifications of 7.62x51 is the port pressure. The gas port of a M14 is (say) 12" forward of the chamber. NATO ammo will meet a specified minimum and maximum pressure at that position.

A fast powder drops pressure fairly quickly as the bullet moves down the barrel. A slower powder, as is used on heavier bullets, drops pressure more slowly, so the port pressure at the 12" point would be higher. If the port pressure is too high it beats up the gas system.

A SAAMI (civilian) test barrel has only one place where pressure is measured - at the chamber. A military spec test barrel has two pressure test points. One at the chamber and another at the location of the M14 gas port (7.62x51) and the 5.56 military test barrel has a second place where the M16 gas port is located.

The IMR test lab at Valleyfield, Quebec has a set of SAAMI test barrels and also a set of NATO test barrels since they make powder for military applications.

The Canadian gov't lab at Bells Corners, Ontario has a special 308 test barrel made from an Obermyer 7.62 target rifle barrel. This barrel is tight, as used to be favoured by target shooters, measuring .3065 x .299 and is 30" long.

You asked about the M14 and Enfield. If I was to use commercial ammo in a Garand or M14, I would only use 150 gr or lighter bullets. This would probably have port pressures similar to NATO standard. But only NATO military ammo would guarantee me that the ammo was ok. Using commercial ammo is not a safety issue in these rifles, but a durability issue. High port pressures can break things - like op rods.

As for the Enfield, it is a bolt action. Use 308 or 7.62. Similar pressures


As for the Enfield, it is a bolt action. Use 308 or 7.62. Similar pressures.
 
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GANDERITE said:
Quote: "So that would apply to converted Garands as well? What about a 7.62 Enfield?"

As I mentioned in my post above, one of the specifications of 7.62x51 is the port presure. The gas port of a M14 is (say) 12" forward of the chamber. NATO ammo will meet a specified minmimum and maximum pressure at that position.

A fast powder drops pressure fairly quickly as the bullet moves down the barrel. A slower powder, as is used on heavier bullets, drops pressure more slowly, so the port pressure at the 12" point would be higher. If the port pressure is too high it beats up the gas system.

A SAAMI (civilan) test barrel has only one place where pressure is measured - at the chamber. A military spec test barrel has two pressure test points. One at the chamber and another at the location of the M14 gas port (7.62x51) and the 5.56 military test barrel has a second place where the M16 gas port is located.

The IMR test lab at Valleyfield, Quebec has a set of SAAMI test barrels and also a set of NATO test barrels since they make powder for military applications.

The Canadian gov't lab at Bells Corners, Ontario has a special 308 test barrel made from an Obermyer 7.62 target rifle barrel. This barrel is tight, as used to be favoured by target shooters, measureing .3065 x .299 and is 30" long.

You asked about the M14 and Enfield. If I was to use commercial ammo in a Garand or M14, I would only use 150 gr or lighter bullets. This would probably have port pressures similar to NATO standard. But only NATO military ammo would guarantee me that the ammo was ok. Using commercial ammo is not a safety issue in these rifles, but a durability issue. High port pressures can break things - like op rods.

As for the Enfield, it is a bolt action. Use 308 or 7.62. Similar pressures.
Click to expand...

Thanks really good stuff. :D
 
OK, I checked the article on the link and see the problem. "Cartridges of the World" has a section that represents the US Army spec sheets. As my posting explained, the Army was using CUP data but called it "PSI", which leads to the impression (false) that NATO ammo is low pressure.

The author of the linked article, like may others, has picked up on this difference in pressure spec for 7.62 v 308 and has assumed the pressure limits are different.

It would be like an American looking at our speed limits signs and thinking we can drive faster here.

The truth is actually buried in the last article in the link, where they test some Federal low pressure ammo. As part of the test they fired some full power 7.62 NATO in an Ishy. Velocity was 2775.

If we go to a loading manual and look up 308 Win and the Max loads with the 150 gr bullet and 4895 powder, we see similar or lower velocities as the NATO in the Ishy.

Hmmm. Max 308 velocity is about same as NATO. Does not look like the NATO has a 10,000 psi disadvanatge, does it?

I am going to check my files and see if I have any test reports from the gov't lab for NATO and 308. I threw out a lot of that stuff, but still might have something. Readers might like to see what it looks like.

Then I have to figure out how to use my scanner....
 
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OK, I found some pressure test data. This is test results obtained by Energy, Mines and Resources at their Canadian Explosives Research Laboratory, Bells Corners Complex (Ottawa).

These tests were part of a program to develop target rifle ammunition that would be suitable for target rifles using barrels tighter than the official 308Win dimensions. The tests involved shooting various types of ammo in a SAAMI barrel (the official 308 barrel) and a DCRA barrel (a tight chamber throat and barrel). I was trying to develop ammo that would not exceed 62,000 psi in the DCRA barrel. As a reference, I used some IVI NATO 7.62 that I knew was causing pressure problems, This ammo developed about 55,000 psi in a standard barrel and about 63,000 psi in a DCRA barrel.

The two little arrows on the left show Winchester made 308W and ordinary IVI 7.62x51 ammo shot in a standard 308W barrel. The far right table shows the pressures – about the same - 55,800 and 55,000.

If you are looking for official confirmation that 7.62 NATO and 308Win are about the same pressure, here it is.

The bottom table shows the test results of the reference ammunition that I use in my pressure gun. Basically, these two lots of ammunition (one is 308, the other is 7.62 NATO) are known lots of ammo at the top end of the allowable pressure specification. All ammo we make must be milder than these two lots of reference ammo. Our pressure gun is not officially calibrated, but it does reliable compare one load to another. So if the ammo we make is milder than these two loads, we know it is ok. From time to time we submit ammo to the gov’t lab to see what pressures actually are.

The table at the bottom once again shows that a box of commercial 308Win had about the same pressure as a box of NATO 7.62. In this case, over 62,000 psi in a target rifle barrel.

testsummary.jpg



This is an actual raw data sheet from a test. Every pressure lab in North America has a case of the official reference ammo for each caliber. The 308Win reference ammo is made by Winchester. At the start of every test they shoot same reference ammo to calibrate the gun. This page shows the reference test, Lake City Match (US ARMY NATO) and Norma Match (308 Win).

The form is in French. The line “Moy corr.” means “Corrected Average Pressure”. It shows:
Winchester 308 was 55,800 psi,
Lake City Match (NATO) was 60,180 psi,
Norma Match (308 Win) was 52,060

In conclusion, 308 and 7.62 NATO operate at similar pressures and any given box will generate 55,000 to 60,000 psi. After many tests, I have not seen any trend of one type being hotter or milder than the other. As an ammo manufacturer who talks to others in the business, the one difference I know is that ammo manufactures worry about lawsuits, NATO does not. More than one of us has made a corporate decision to keep well below the allowed limits. One major manufacturer told me his limit was 57,000 psi.

testdatasheet.jpg


Before ammuntion can be sold in Canada it has to be "approved" and put on the approved list. This includes inspection and approval of the packageing and labeling (warnings must be bilingual, for example). And, of course, the ammunition must be approved for pressure/velocity. This aproval process includes approval of the components. One cannot have ammuntion aproved if it does not use approved powder.

This particular test involved testing of 11 different boxes of 308 and 223 match ammo. $45 per box of 20 rounds seems to me to be a very reasobable price for this service. Anyone wanting to have their pet load tested might be able to do so. The cases would have to be for a standard case (no wildcats) and full length sized, of course.

CANMETLETTER.jpg
 
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Ganderite,that is very exhaustive and informative data.Would you happen to have any lab tests concerning the accuracy of 7.62 ball ammo (IVI/DA/other),incl DND acceptance standards for accuracy? I see comments about "internet groups " printing MOA or better with military ball,but my own experience over the yrs tells me that anything better than 2 MOA is gravy.I do, however, allow for acts of God and random bullet dispersion yielding the odd sub-MOA group and have been blessed with this from time to time,but certainly not on a predictable/regular basis.
 
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