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7.62 NATO and .308 Winchester

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Smokey View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Smokey Quote  Post ReplyReply Direct Link To This Post Topic: 7.62 NATO and .308 Winchester
    Posted: October 11 2009 at 6:11am
The WWII .30-06 M2 Ball specifications required 835 m/s (2,740 feet per second) velocity, measured 24 m (78 ft) from the muzzle. Muzzle velocity was 2,805 ft/s.
The 7.62 NATO does close to the same with a smaller cartridge.
I believe the M2 Ball operated with a peak pressure of around 45,000 PSI. The NATO cartridge peaks at about 50,000 psi to get the same velocity. .308 Winchester ammo can run much higher, with a maximum of 62,000 psi. I would not want to run any "regular" No.4 Mark1 or 2 with ammo at those pressures. Headspace will be increased. The Indian rifle uses a higher-strength steel for the action to handle the NATO cartridge, but again I'd stay away from the non-NATO ammo.
In any event, reloading allows the use of milder loads that extend the life of your rifle.
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Stnwll2 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stnwll2 Quote  Post ReplyReply Direct Link To This Post Posted: October 11 2009 at 7:25am
What I don't understand about the whole 308/7.62 issue is ..... Isn't it essentially a physics problem?

Given the same weight projectile and the same velocity shouldn't the pressure be the same out of the same rifle?

147/150 grain FMJ bullet moving at about 2800 fps.  Doesn't that math problem give you the same pressure assuming the same rifle?

Why should it take more pressure to move the .308 than the 7.62?  If the .308 developed more pressure shouldn't the velocity be significantly higher too?

I stood in the ammo isle of the local Sportsman's Warehouse looking at all the .308 ammo, with 150 gr slugs and heavier and all of them had roughly the same velocity listed.  I can see that the heavier bullets may require higher pressure.

I have a degree in History so there very well could be a math subtlety that I'm missing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: October 11 2009 at 10:03pm
Hoo Boy! Get the popcorn, this may take a while.Confused
 
The .308 Winchester is the civillian version of the 7.62mm NATO round.
There are minor tolerance differences in the spec drawings for the 2 cases.
 
The 7.62mm NATO round is frequently made with thicker brass (to better handle the violent cycle of full auto weapons.)
 
SAAMI use one method to measure pressure during firing & NATO use a different method that uses a different unit of measurement. Because of this & several other things there is a lot of confusion about the actual pressures generated during firing the 2 rounds in an identical chamber.
 
Because of the thicker brass with the same external dimensions the volume inside the 2 cases differs. IF you're reloading you need to lower the charge weights to allow for the lower internal volume.
Also there are some rifles that won't run well with some commercial loads (The Garand being a major example).  The Garand's design has an inherant weakness. Ithe dog leg operating rod can be bent with heavy bullets & slow-burning powders! Not a defect for military use as the medium speed powder & 150 gr bullets worked perfectly, but if you were to load say a 220 gr bullet with a slower burning powder you'd have a problem.
 
Powders vary as well. the same volume of unburnt powder gan produce differnt volumes of gas, and at different speeds. Because of this there is a curve of pressure because "gunpowder" doesn't "explode" it burns fast. The peak of the curve can create temporary pressures that are above the safe limits for the case & action.
 
The 2 methods of measuring pressure come into play here.
One measures only the total effect of the pressure at the end of the cycle. The other actually measures & graphs the curve in real time as it happens.
 
As you can imagine this gets slightly different answers to the same question. Now throw in for luck the differences in the units of measurement & add the fact that one is called "PSI" but is NOT "Pounds Per Square Inch" & the source of confusion becomes easy to understand.
Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Edward Horton Quote  Post ReplyReply Direct Link To This Post Posted: October 12 2009 at 7:12am
< ="-" ="text/; =utf-8"> < name="GENERATOR" ="Office.org 3.0 Linux"> < ="text/"> < ="-" ="text/; =utf-8"> < name="GENERATOR" ="Office.org 3.0 Linux"> < ="text/">

Did you ever hear anyone say if you shoot commercial 30-06 ammunition in a military 03-Springfield your Springfield 03 would blow up?

The rumor mill started about the .308/7.62 and chamber pressures because some people do not understand the difference between the older copper crusher method and the newer transducer method of measuring chamber pressure.

On top of this the military manuals use the older copper crusher method and list the chamber pressure in PSI.....BUT remember it is in the older CUP (copper units pressure) which is also read as PSI or pounds per square inch, NOT to be confused with the transducer method which is also read as PSI.

What you need to realize is 50,000 CUP is equal to 60,000 PSI just as 60 MPH is equal to 100 KPH. On paper there is actually less than 200 PSI difference between the .308 Win and the 7.62 NATO which is insignificant. In reality the .308 actually generates LESS pressure than the 7.62 NATO because the American ammunition manufactures load there ammunition below the maximum allowed chamber pressures.

In closing as you can see below if put 220 kPa in your tires they will blowup and kill everyone in a 50 yard radius, but if you only put 32 PSI in your tires you will be perfectly safe and your tires will not blow up. Wink

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Cookie Monster Quote  Post ReplyReply Direct Link To This Post Posted: October 12 2009 at 7:12am

There is several post on this topic if you wish to search for them. Ask Tony he has archived many of these

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Stnwll2 Quote  Post ReplyReply Direct Link To This Post Posted: October 12 2009 at 1:26pm
Soooooo ....

The fact that My 1965 2A1 didn't blow when I shot 20 rounds of American Eagle 308 though it shouldn't surprise me. 150gr, 2780 fps (-ish) .... about the same as Nato.

Beer
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Quote  Post ReplyReply Direct Link To This Post Posted: October 12 2009 at 3:12pm
There have been arguments on other forums regarding pressures and Nato ammunition and I'm not getting involved in an argument on here. All I will say is comercial ammo is made to suit MODERN rifles which haven't been ill used they are of a stronger construction using modern steel and different bolt locking formats. The forum doesn't take ANY responsibility for anybody using ammunition of their choice in their weapons.The archive material has been posted as a guide read it then make your own decisions.You should all have loading data from a reputable source email Hornady, Sierra, Lynman or Vhitavuouri and ask their advice! Don't rely on an "internet expert ". The above make ammunition or powders etc THEY are the experts.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Quote  Post ReplyReply Direct Link To This Post Posted: October 12 2009 at 9:56pm
As Disraeli said there are lies Dammn lies and statistics. Stats can be bent to suit any circumstance so ASK THE EXPERTS! 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Edward Horton Quote  Post ReplyReply Direct Link To This Post Posted: October 13 2009 at 12:52am
< ="-" ="text/; =utf-8"> < name="GENERATOR" ="Office.org 3.0 Linux"> < ="text/">

The Truth About 308 Win and 762 NATO


A little info that some people might find interesting that is not over exaggerated or based on urban myth.


The Truth About 308 Win and 762 NATO

http://home.comcast.net/~ehorton/The...d 762 NATO.pdf


Is it safe to shoot 308 Winchester in a rifle chambered for 7.62 NATO?
What about 7.62 in a 308?
By Jim Bullock

http://www.smellysmleshooters.net/ammopressure.htm


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Edward Horton Quote  Post ReplyReply Direct Link To This Post Posted: October 13 2009 at 1:05am

Pressure convershion chart CUP to PSI




The U.S. Army manual is written in CUP (copper units pressure) BUT it still is read as PSI or pounds per square inch, the pressures given below are not in the newer transducer method which are also read as PSI.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Quote  Post ReplyReply Direct Link To This Post Posted: October 13 2009 at 4:03am
 You're the person involved in the argument on the other site aren't you?? You wound up the other members!! I suggest you read your own links RE WEAPONS IN GOOD ORDER. As I said in my first reply we do NOT know if the weapons any of our members is using has been abused prior to the member purchasing it.ERGO THE FORUM DOES NOT ACCEPT RESPONSIBILITY FOR ANY MEMBER USING UNSUITABLE AMMUNITION IN THEIR WEAPONS!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Shamu Quote  Post ReplyReply Direct Link To This Post Posted: October 13 2009 at 4:07am
Originally posted by Stnwll2 Stnwll2 wrote:

Soooooo ....

The fact that My 1965 2A1 didn't blow when I shot 20 rounds of American Eagle 308 though it shouldn't surprise me. 150gr, 2780 fps (-ish) .... about the same as Nato.

Beer
YupClap
What you've discovered is the difference between the real world, where bumble bees buzz happily hither & yon, & the thoeretical world where the bumble bee is incapable of flight, mathematically speaking.Wink
Don't shoot till you see the whites of their thighs. (Unofficial motto of the Royal Air Force)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Edward Horton Quote  Post ReplyReply Direct Link To This Post Posted: October 13 2009 at 4:26am
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Tony you are a moderator, since when is posting published facts to clear up confusion and stupidity considered stirring up the natives or making trouble.


I have NO idea what you are talking about in your above posting or are all moderators as insulting as you are in this forum. Your above posting smells of “burn the witch or “off with his head” for presenting proven facts instead of rumors.


IF you can PROVE that any of the material I have posted here is incorrect then please present facts to the contrary otherwise save your insults for a PM instead of an open forum.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Quote  Post ReplyReply Direct Link To This Post Posted: October 13 2009 at 4:51am
My comment is simple! We do not accept responsibility for persons using ammutniton unsuitable for their weapon! Your post states weapons in GOOD order THAT IS THE POINT I AM MAKING! As a moderator I have a responsibility for the safety of the forum members!
 TO AVOID ANY FURTHER PERSONAL ATTACKS I AM LOCKING THE SUBJECT!

Published facts! http://www.surplusrifle.com/shooting2006/308vs762nato/index.asp
Rottie (PitBulls dad.)


“If electricity comes from electrons, does morality come from morons

Born free taxed to death!!!

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Cookie Monster Quote  Post ReplyReply Direct Link To This Post Posted: October 13 2009 at 6:16am
Enough is enough lets resolve this in a civil manner whan is a good time to discuss this in the chat room. Let me know what is a good time ?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Quote  Post ReplyReply Direct Link To This Post Posted: November 03 2009 at 7:24pm
Ok GENTLEMEN I have unlocked this thread now things have calmed down. I'll be keeping a watchful eye on things in here as well as the forum in general.
Rottie (PitBulls dad.)


“If electricity comes from electrons, does morality come from morons

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