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

Steve, I'm afraid your links are no more credible than the rag you mentioned in your first post. I didn't read all of them, mostly because there were so many mistakes it wasn't worth continuing.

I don't consider anything on the internet as "fact" unless it's from a reputable source. This isn't either, but I am going to try to verify the information in post nine on the chamber dimensions as it appears your source on the "headspace" issue is pretty wrong.
7.62 x 51 mm and .308 winchester - M14 Forum
 
The 223/556 argument never ends. I've heard "experts" say it's OK to shoot 556 out of a 223-stamped gun while others say you shouldn't.
 
I tend to ask the maker.

Springfield said I could use 7.62 or 308 in my M1A.

Ruger said I could use 223 or 5.56 in my Mini 14.

Ruger also said to only use 223 in my #1.
 
Jellybean said:
Steve, I'm afraid your links are no more credible than the rag you mentioned in your first post. I didn't read all of them, mostly because there were so many mistakes it wasn't worth continuing.

I don't consider anything on the internet as "fact" unless it's from a reputable source. This isn't either, but I am going to try to verify the information in post nine on the chamber dimensions as it appears your source on the "headspace" issue is pretty wrong.
7.62 x 51 mm and .308 winchester - M14 Forum
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I'm not seeing any difference the headspace data in your link and the one I quoted.:confused::confused::confused:

As for confusion over pressures, I see much of it on the M14 forum and in that thread. Consider the factors for confusion:

1) NATO/CIP have their test standards and the answers are in PSI.

2) SAAMI have a different test standard and the answers are also in PSI, but will be slightly different from the NATO/CIP values for the same round.

3) Back in the day the US used CUP to judge chamber pressure and it gives readings in the same order of magnitude as PSI measurements with the same ammo, but CUP readings are different enough to cause problems.

4) Add poor attention to detail, lack of the appreciation for scientific units leading to careless mixing of PSI and CUP, and throw in a liberal dose of poor reading comprehension (ain't got no time fo dat :D) and guess what you get? ;)
 
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The .223 vs .556 can get real confusing with its labeling. Some ammo is labeled both (.223/5.56). Which is it? Some just .223, other just 5.56. I've been told some ammo labeled .223 is really 5.56. Is it really?

In any case, I've shot it all in my .223 M70, my dad has shot it in his ruger #1. It has all been fine. I suspect the most important factor is the real heavy bullets may not stabilize due to the slower twist rate. 62 gr is the heaviest I've used.

I have a hard time believing that a m70 or #1 chamber is weaker than an ar15 chamber.
 
johngalt said:
The .223 vs .556 can get real confusing with its labeling. Some ammo is labeled both (.223/5.56). Which is it? Some just .223, other just 5.56. I've been told some ammo labeled .223 is really 5.56. Is it really?

In any case, I've shot it all in my .223 M70, my dad has shot it in his ruger #1. It has all been fine. I suspect the most important factor is the real heavy bullets may not stabilize due to the slower twist rate. 62 gr is the heaviest I've used.

I have a hard time believing that a m70 or #1 chamber is weaker than an ar15 chamber.
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No differences (okay a very, very slight difference in capacity that won't matter) in the cases. The differences is the military rounds are typically longer than sporting .223s, so 5.56-chambered rifles have a longer throat than sporting .223 rifles. A 5.56 round may cause the bullet to engage the rifling in a .223 chambered rifle, and thus raising pressures. If you chamber a longer 5.56 round and after ejecting it find no rifling marks on the bullet, your throat is probably long enough.

Secondly, military rounds are hotter than sporting .223s. Will sporting rifles handle the higher pressures? Maybe, maybe not.

I've noticed most ARs are compatible with both rounds, but a few are .223 only chambered. Why a box of ammo would be marked .223/5.56 is beyond me and sets the stage for a possible accident.
 
I would suspect that ammo marked 223/556 is considered by it's maker to be safe to use regardless of the chambering specs and throat dimensions. I have used both interchangeably for years with no difficulty in quite a few different rifles.
Military chambers are often a little generous (to allow for dirty ammo) and may well have a longer throat but I really doubt there is a significant difference between commercial and military loads with the same weight bullets. I can see where a tight, match spec chamber in 223 could have problems with mil spec ammo but it could very well have trouble with some 223 commercial stuff as well. As more than one poster already mentioned, pressure measuring methods vary and it's not easy to relate one system to another.
 
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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.
 
There is a velocity/pressure difference between .223 and 5.56, it is quite common for ARs with .223 chambers to shed crimped in primers while firing 5.56.
 
Arik said:
308 was a copy of the 7.5 French!

Sent from my SCH-I545 using Tapatalk
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I know that this is an ancient thread, but the .308 was modeled after the .300 Savage cartridge after WWII, not the 7.5 MAS. Virtually identical to the .300 case, except the 7.62/.308 has a longer case neck, to more firmly hold the bullet when used in full auto weapons.
 
Another ferinstance....

I found out that the large difference in 5.56 NATO and .223 is that testing method, including the location of the transducer, is WAY different. And that the throat on the 5.56 is made to accommodate different rounds that could over pressure a .223.
 
johnbeaver said:
Zombie much.
I thought the .308 was a cu down '06?
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That was exactly the rationale of the .300 Savage just after WWI. The Savage Model 99 rifle had been on the market for 20 years, but it had a fairly short action, too short to accommodate the .30-'06 cartridge. After WWI, it occurred to Savage that it might be easier to market the Model 99 if it could be chambered for a cartridge more or less equivalent in power to the .30-'06, so it would appeal to all those Doughboys returning from France where they became very familiar with .30-'06 rifles such as the Springfield '03 and the Enfield 1917. So they just shortened the .30-'06 case so that the loaded cartridge length was short enough to work through the Model 99 action and could be loaded to approximate .30-'06 ballistics, as the Savage 99 action was quite strong. It worked.

During and after WWII, the U. S. Army was looking for new rifle and machine gun designs which would be lighter and handier, and that would necessarily require a lighter and more compact cartridge, preferably one which was already in use, eliminating a lot of ammunition development cost. The .300 Savage best met that requirement. However after some testing, the Army decided that the stubby case neck of the .300 Savage did not provide adequate support to hold the bullet firmly enough for use in full auto weapons, so they simply lengthened the .300 Savage case neck a bit. And Voila! - the 7.62x51 (.308 Win) was born.
 
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