Rant: Another gun rag gets .308 vs 7.62 NATO wrong

[Echo40]

Old thread, but I can relate to the TC's irritation towards the authors of various articles spreading misinformation because unfortunately Investigative Journalism is a lost art, and sensationalism generally attracts attention better than boring old factual information ever will amongst the sort of ignorant folks who act as if it is unreasonable to be irritated by the spread of misinformation.

Fortunately, times change, and in most circles I'm aware of, most folks in the know will tell you that 7.62 and .308 Winchester are indeed interchangeable, so the only folks it effects are the sort who acts like such misinformation isn't worth getting upset over.

It reminds me of the modern day attitudes towards .40 S&W now that it's no longer popular in Law Enforcement and all the articles making blanket statements about how 10mm Auto being a more powerful cartridge without getting into load data or actual facts, so you get ignorant people posting around forums about how their 10mm is more powerful, yet all they ever shoot are 10mm Lite/FBI which is downloaded to similar specs as your average 180gr .40 S&W self-defense load, thinking that they have something substantially more powerful. Don't even get me started on the nonsense about 10mm being as powerful as .41 Magnum.

 

[DWalt]

Doncha just love how certain inaccuracies become fact and refuse to die no matter how many times the truth is spoken. Yes, it's 7.62 NATO vs .308 Winchester AGAIN. Shooting Times trotted out the old fiction about .308 Win being a 62,000 psi cartridge and 7.62 NATO is only 50,000, so has much less pressure. WRONG,WRONG thrice again WRONG.

The 62,000 psi figure for 308 Winchester is the latest SAAMI pressure measured using a piezo pressure transducer. The value for 7.62 NATO comes from an old Copper Units of Pressure (CUP) style measurement, and the answer is indeed 50,000 CUP. It's like saying the distance between two points is 62 miles and somebody says, "No, it's much further, like 100 km". Unfortunately there is no "laws of physics" based PSI to CUP conversion, but empirical data does show a relationship. http://www.shootingsoftware.com/ftp/psicuparticle2.pdf

Shortly, somebody will appear and say "Ah, but it's 50,000 psi CUP". There's no such unit of measure. It's like measuring your inseam in grand pianos per decade. Don't go there.

A fuller explanation is to be found here. Chamber pressures | M14 Forum
The NATO and SAAMI chamber pressure test methods both use piezoelectric pressure gauges, but there the similarity ends. And the ancient copper crusher method is entirely different from both. Actually, the European CIP method is similar to the NATO method in principle. All four tests produce a chamber pressure number but not the same number for the same load. The CUP method is obsolete today and it is doubtful that it is still used anywhere. Sort of like comparing a sundial to an atomic clock if you want to know the time.

 

[murphydog]

Still good information, and in four days we can wish this thread a happy 10th birthday!

 

[sigp220.45]

I treat .223/5.56 and .308/7.62x51 as completely interchangeable and save those brain cells for something else. No problems in the last 50 years or so.

 

[LVSteve]

A fuller explanation is to be found here. Chamber pressures | M14 Forum
The NATO and SAAMI chamber pressure test methods both use piezoelectric pressure gauges, but there the similarity ends. And the ancient copper crusher method is entirely different from both. Actually, the European CIP method is similar to the NATO method in principle. All four tests produce a chamber pressure number but not the same number for the same load. The CUP method is obsolete today and it is doubtful that it is still used anywhere. Sort of like comparing a sundial to an atomic clock if you want to know the time.

The trouble usually starts when somebody sees the old NATO CUP number and compares it with the modern piezo methods.

 

[erikpolcrack]

I remember this debate somewhat. I think the warning was meant for those using older mil-surp rechambered rifles from the turn of the century. I'm vague on the whole debate.

That's exactly how I remember this discussion, as being primarily about not shooting 308 Win in imported Spanish 1893 and Chilean 1895 Mausers being import marked as 308 Winchester. The point was made that they were re-barreled/rechambered for 7.62 NATO as potential wartime reserve/militia weapons. The differences between the two rounds was enough that it wasn't safe to fire 308 Win in those 130-year-old rifles originally designed around the 7mm Mauser.

 

[6string]

As a handloader, here’s how I approach the subject. And, avoid trouble!
To begin with, I only shoot my own loads, unless I’m shooting up factory stuff to get the brass.

1). All loads are matched to the specific firearm in which they are to be used.
2). Military brass (ie: 7.62 or 5.56) has crimped primers and reduced capacity. (Keep the latter in mind even if converting to another caliber.). Develop loads and process brass accordingly.

PS: I don’t understand why there were so many replies mocking to OP. It’s an important topic that some people want clarified.

 

[ImprovedModel56Fan]

I treat .223/5.56 and .308/7.62x51 as completely interchangeable and save those brain cells for something else. No problems in the last 50 years or so.

I don't know whether that is right, but I do it, too.

Hope some of you pay attention to me when I DO know what I'm posting about.

 

[LVSteve]

PS: I don’t understand why there were so many replies mocking to OP. It’s an important topic that some people want clarified.

I can tell you exactly why. I had the temerity to suggest that some people's beloved .308 Win was not a dragon slaying monster when compared to 7.62 NATO. As somebody who previously worked in high end metrology, I have found that hard proof often gets up people's noses.

Years before I wrote the OP I read on another forum a guy who actually worked in an EPVAT rated facility in Canada and tested ammo said he had seen NATO ammo regularly equal and even surpass the .308 SAAMI spec on his test rig. A whole bunch of pitchforks and torches were handed out then, too. I tried to find that forum again when I posted the OP for this thread, but looks like it got lost in one of the corporate forum takeovers.

 

[46er]

I think I lucked out, the link does not work!!!

 

[Yendor357]

I am going to beat my favorite dead horse yet again.

Buy a Chronograph. Although Velocity is not an absolute measure of chamber pressure, it’s a pretty good indication. And in the end, velocity is all that matters.

 

[DWalt]

I am going to beat my favorite dead horse yet again.

Buy a Chronograph. Although Velocity is not an absolute measure of chamber pressure, it’s a pretty good indication. And in the end, velocity is all that matters.

Under the same conditions and circumstances, the MV is proportional to the peak chamber pressure, but it is not a simple linear relationship. If you have the Quickload computer program you can work it out.

 

[cd228]

I can tell you exactly why. I had the temerity to suggest that some people's beloved .308 Win was not a dragon slaying monster when compared to 7.62 NATO. As somebody who previously worked in high end metrology, I have found that hard proof often gets up people's noses.

Years before I wrote the OP I read on another forum a guy who actually worked in an EPVAT rated facility in Canada and tested ammo said he had seen NATO ammo regularly equal and even surpass the .308 SAAMI spec on his test rig. A whole bunch of pitchforks and torches were handed out then, too. I tried to find that forum again when I posted the OP for this thread, but looks like it got lost in one of the corporate forum takeovers.

Good on you for fighting for the Facts.

Also, Sweet baby Jane, this is an old thread.

 

[hkcavalier]

Now can we discuss 9x19, 9mm NATO, 9mm +P, 9mm +P+, and 9mm Major?

 

[LVSteve]

Now can we discuss 9x19, 9mm NATO, 9mm +P, 9mm +P+, and 9mm Major?

There's probably a zombie thread out there to revive on those subjects, but this time I didn't start it.

 

[OutAtTheEdge]

I'll just pretend I understand what you're talking about.I'm still awed by the fact that socks can go on either foot.

I actually have a pair of "performance socks" that my wife gave me, that are marked L and R. One day on a whim, I intentionally put them on the wrong feet. Laced up my shoes, stood up and took one step. Ran smack into myself.

 

[rwsmith]

I need to put Quickload .......

Under the same conditions and circumstances, the MV is proportional to the peak chamber pressure, but it is not a simple linear relationship. If you have the Quickload computer program you can work it out.

...on my 'Things I want' list. Maybe Libre or somebody will come out with a clone.

 

[djohns6]

By the time I finish typing this I will have forgotten what I read and it won't matter anyway ...

 

[Skeet 028]

Back a few years I did a lot of shotgun shooting which equated to a LOT of reloading. I shot a K-80 in skeet with Briley and/or Kolar tubes. We shooters noticed quite a few split chambers in the 20 ga. Briley did some checking and found that a perfectly safe 20 ga load through the years had really high spikes in pressure when checked by PE testing. Lead crushers never read the very high momentary pressure spikes. They let it be known that we should switch powders in the 20 and 28 if loading Green Dot. . I used Unique or Herco in both and never split a tube. Just an illustration about the differences between crusher pressures and Piezo Electric testing

 

[jimmyj]

GEE, THANKS. Now I have something else to keep me awake when I should be getting my beauty sleep. (I really, really need more beauty sleep)