7.62 nato what is it?

Devil's advocacy time: how strong are the DCRA Longbranch rifles, with regard to .308 ?

When the DCRA and other Longbranch rifles were converted, they were never intended for the hot commercial 308Win. They were intended for 7.62x51 Nato spec ammo, which isn't all that much hotter than the original 303 British round.

Something else, just to show how the No4 rifles have been converted, back in the seventies, a friend of mine converted a No4 to 8x57. He did it for two reasons. One he liked the cartridge and wanted something with a larger diameter than the 303 and 8mm barrels were plentiful and cheap. Two, he firmly believed that the No4 actions were much stronger than believed by many at the time. He was an engineer and knew metallurgy very well. By his calculations, the No4 was capable of digesting 50,000+ psi CUPs as a steady diet. They were made to handle all sorts of issues that occur under battlefield conditions, like a muzzle jammed into the dirt or mud and go unnoticed in the excitement that ensued and have the soldier fire it out, albeit unintentional, without harm to himself or the weapon.

By the way, he fed it a steady diet of surplus 8x57 from various nations. He also hated commercially available loads. He would pull the bullets in the surplus, same as we do with the 7.62x39 and replace them with soft point ammo of similar weight. Those were snappy enough for his desires.

The No4, supposedly stretches a bit when fired and the snapping back into form is supposed to make it stronger, as well as enhance accuracy. Personally, I don't think it is any more elastic than any other receiver.

I do think they are a lot tougher than given due credit for.
 
Bearhunter said: "I say this because most Nato 7.62x51 is loaded to around 45,000 psi."

Claven2 said: "The NATO ammo it is designed for is much lower pressure."

NATO and 308 have almost identical pressure limits, around 60,000 psi. I have seen production lots of both commercial 308 and IVI 7.62 over 60,000.

The myth of NATO being lower is because the military used to quote CUP units, which was a smaller number than the PSI quote for 308. But it was like comparing mph to kph. Different numbers, but the same speed.

As for the FR7 and FR8, I have a FR8 and love it. Excellent sights and a nice rifle. I shoot anything in it.

I have had a number of small ring Mausers in 308 and 358, including 2 Spanish, and have fired them a lot with full power ammo. I don't have a FR7, but if I did, i would not hesitate to shoot commercial 308 and milsurp in it.

I recall that many 308 target rifles were built on the Swedish small ring actions. They fired hundreds of thousands of rounds without incident.
 
OK, now I have to go back and check my information sources.

Ganderite knows his stuff. I won't agree with him on this but he's good enough at what he does to take notice.

As for the M96 Mauser actions. The cartridges he mentions were built on later actions. There is a lot of controversy as to whether the metal in the later actions is stronger than the earlier actions. If so, the comparison is moot. Personally, again I have to go by what I can glean from old books and the internet. Sadly, there isn't really any proven consensus.

I've also seen the old US 98 Krag actions converted to 308 Win. Never saw one Kaboom or even heard of it.

There was also a time when an entrepreneur in the states was converting 91/30 Mosins to 30-06. There was a hue and cry that these rifles were grenades waiting for the right ammo.

The 30-06 cartridge was loaded to around 47,000 CUP right past WWII for the military. The 7.62x51 Nato was designed to operate under similar pressures in similar firearms. US government specs for the ammo used in the M14 was 50,000 psi maximum and I believe the unit of measure was copper units of pressure as derived from the measurement of pure copper billets that were crushed when fired in test receivers.

My source for this is The Book of Rifles by WHB Smith and Joseph E Smith.
 
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Back around 1975, I used to be the proud owner of a package of rifles that I bought from the SIR store in Winnipeg. The package consisted of a converted 98 Mauser, Belgian FNFAL and a TRW M14. All were ex IDF firearms from Israel.

The Mauser and M14 digested any ammo that was put through them without any issues at all. The Belgian FNFAL was fussy. If I used US Frankford Arsenal made ammo in it, I could guarantee an extractor, spring and plunger would get ripped out and disappear.

The US FA ammo was obviously hotter.

I did a personal test, which I won't claim to be definitive for anything other than my own curiosity and to solve a personal problem with the FAL.

It has also been rumored that Canadian FNC1A rifles suffered from similar issues with US ammo but I can't say I've seen it personally. Maybe someone with hands on experience can confirm or deny this???

Anyway, I tested Canadian made IVI, DCRA issue ammo as well as, South African, Israeli, British and US Frankford Arsenal ammo, which by the way was the most available at the time.

The only ammo that gave me problems in the FAL was the Frankford Arsenal stuff. The cases were similar in weight and construction. The US and Canadian offerings were Boxer primed and the others were all Berdan primed. All of the bullets were approximately 150 grain fmj SPBT.

I pulled ten bullets from each manufacturer and all except the US FA cartridges were loaded with ball powder. The US FA stuff used an extruded powder that resembled the IMR stuff available at the time. I suspect IMR 4895 which averaged 45 grains in weight on my balance beam scale.

All of the bullets averaged 150 grains. The charge in the ball powder loaded cartridges were between 45-47 grains.

The Chrony I had back then left a lot to be desired. It was one of the first shadow models available and was quite unreliable from one moment to the next. To get consistent results with it, I had to make up an artificial light source, consisting or 12v head lights held over the screens and powered from the batteries in my pick up.

The Canadian and European offerings all measured around 2700fps, +/- 50 fps. The US FA offering was slightly over 2800fps +/- 50fps. I will note ow that the Canadian and European offerings shot around 2+ inches and the POI was almost identical. The US FA ammo was noticeably stouter in felt recoil and printed at least 4 inches higher and the groups were around 4 inches in diameter.

The rifle I used for testing velocities was the 98 Mauser.

When I reloaded the cases I pulled apart previously, including the US FA stuff I reloaded the all with 47grains BLC2, which I knew delivered around 47,000 CUP.

I shot all of those rounds out of the FAL because I knew it was a safe load from previous tests. It was also an accurate load with most of the FMJ BT bullets going into 2inches at 100 yards. All of the different manufacturers followed similar specs as far as bullet weights and shapes go. All of them also made their cases to very similar weights, give or take a couple of grains. Not bad at all. All velocities were around 2725fps +/- 20fps. The closer velocity spread was likely because the loads were all weighed individually, rather than thrown.

The consistent performance of all of the cartridges in the FAL, when the cases were reloaded with the same powder and the bullets went into their original cases and all were loaded to the average OAL, which was only a few thou one way or the other, they were accurate and no issues occurred in the FAL.

I made a personal observation that the ammo that was most available, US FA was more powerful in that it delivered higher pressures. It was also problematical in the FAL but fine in the M14 and Mauser. It was also the least accurate of all the manufacturers tested.

It was these tests that I drew the conclusions from that I mentioned in response to the safe pressure guidelines mentioned about the Spanish FR7 rifles, which are built on 93 Mauser actions, made in Oviedo Spain Arsenals. I would also suspect the actions were the best of what was available and not ridden hard and put away wet.

I also suspect the CETME rounds are loaded to around 45,000 CUP. That is why I will shoot some specific NATO 7.62x51 spec ammo in mine.


Like I mentioned previously, this is by no means a definitive test. It was done for my own information so I wouldn't damage a valuable rifle which even though I don't prefer as a battle rifle, I respect and like to shoot.

I sold the FN FAL and M14 long before the classification and registration regs came into law. I regret that but seeing as I wouldn't be able to enjoy them anyway, other than to fondle or store in a safe. Still, I did like the rifles. At the time, an expensive divorce reared its ugly head and they went the way of the willow.
 
"The US FA ammo was obviously hotter. "

I don't know why, but this happens. Some lots of ammo are just much hotter than others. I recall a lot of IVI that was blowing extractors off target rifles. I reported this to the military and they tested it. They reported back to me that it was hot, but at 62,000 psi, still acceptable.

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 wadcutter 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, for some calibers 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 (NATO vs Commercial 308) 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 rifles (M14) 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 case 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.

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 for the last 15 years I 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.
 
Thanks for that Ganderite. Much appreciated.

I have shot a lot of milsurp 7.62x51 out of my FR7. Not thousands but several hundred at least. I have avoided using US made ammo in it, based on my personal tests.

Given your information, maybe I won't be so cautious. Old habits die hard.

IMHO, I go through a lot more effort than most people to make sure my loads are safe and accurate.

That Santa Barbara ammo you mentioned damaged a lot of firearms and even did some damage to the shooters. A good friend of mine had a 98 match rifle damaged and had to have a piece of brass removed from his eyeball. Somehow it made it under his shooting glasses.

International Firearms recalled that ammo if I remember. There were a lot of rumors as to what was wrong with it but nothing definite. That stuff still shows up on occasion.

Again, thanks for sharing your knowledge and experience. Much appreciated.
 
Thanks for that Ganderite. Much appreciated.

Given your information, maybe I won't be so cautious. Old habits die hard.

That Santa Barbara ammo you mentioned damaged a lot of firearms and even did some damage to the shooters. A good friend of mine had a 98 match rifle damaged and had to have a piece of brass removed from his eyeball. Somehow it made it under his shooting glasses.

International Firearms recalled that ammo if I remember. There were a lot of rumors as to what was wrong with it but nothing definite. That stuff still shows up on occasion.

Again, thanks for sharing your knowledge and experience. Much appreciated.

The Santa Barbara incident I referred to involved an out of spec chamber.

The ammo that blew up a lot of guns in Canada and USA was headstamped CBC. I think it was made in Brazil and imported as surplus by Century Arms. I bought many thousands of rounds of it after it was condemned and broke it down for the components.

I was privy to the official report on the problem. At some point in the production run a can of pistol powder got dumped in the powder hopper of the loading machinery. Both the rifle and pistol powder were ball, so not possible to see the problem. Most rounds are 100% rifle powder, a few have some of both and some have enough pistol powder to Kaboom.

Hand loaders often blow up guns the same way.

I have had the occasion to examine many blown up gins over the years (only one was mine). In most cases there were some warning signs before the Kaboom. The Santa Barbara round Kaboomed on the third shot. the first two had serious indications something was wrong.

So if you have a hard extraction or a blown primer you might be getting the only warning God will give you before the kaboom.
 
The Santa Barbara incident I referred to involved an out of spec chamber.

The ammo that blew up a lot of guns in Canada and USA was headstamped CBC. I think it was made in Brazil and imported as surplus by Century Arms. I bought many thousands of rounds of it after it was condemned and broke it down for the components.

I was privy to the official report on the problem. At some point in the production run a can of pistol powder got dumped in the powder hopper of the loading machinery. Both the rifle and pistol powder were ball, so not possible to see the problem. Most rounds are 100% rifle powder, a few have some of both and some have enough pistol powder to Kaboom.

Hand loaders often blow up guns the same way.

I have had the occasion to examine many blown up gins over the years (only one was mine). In most cases there were some warning signs before the Kaboom. The Santa Barbara round Kaboomed on the third shot. the first two had serious indications something was wrong.

So if you have a hard extraction or a blown primer you might be getting the only warning God will give you before the kaboom.


You're right, the cases were marked CBC and it was a specific date stamp IIRC. The box I have is marked REINGESTADA, which is Portuguese for reinserted. I always thought it meant the cases were reloaded.

I was lucky enough to go through the Mannesmann plant in Brazil where they were prepping the truckloads of fired military brass that was brought in for reloading into practice ammo. When I was there, the production dates and codes were all mixed up. It wouldn't surprise me if several thousand similar cases went through the process together.

Thanks for that. There were even rumors that the ammo had been reloaded for Ecuador, which was going through a revolution of some sort at the time and the process was sabotaged. Very unlikely. Your explanation makes a lot more sense.
 
"You're right, the cases were marked CBC and it was a specific date stamp IIRC. The box I have is marked REINGESTADA, which is Portuguese for reinserted. I always thought it meant the cases were reloaded. "

The REINGESTADA ammo was made with necks annealed dead soft. The lack of neck tension made it unusable. So the unpackaged all the bad ammo ( several different lot numbers) and ran it through crimping machines in an attempt to make the ammo usable for something. This did not work very well, so the ammo got sold off as surplus. It would have been good plinker ammo, except one of the lots that got mixed in was the lot that had some rounds with the pistol powder.

If anyone has a case of CBC ammo, pull a few bullets. If they are all loaded with extruded (stick) powder, they are good to shoot. If they are ball powder, pull them and reload with reliable powder.
 
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.

This is what gives historians and writers nightmares - and employment!

I get the feeling we have but touched the tip of the iceberg here.

The question is, how can we get more of this knowledge, yours, bearhunter's and others, into the the public forum?

I can think of some people who have knowledge but will not share it except in dribs and drabs. It will die with them, and instead of being known for their contributions, they will be forgotten.
 
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