[Ultimate_sig]

Well i chose to stay with the 39 i know itll be fun

[MachineHead]

Originally Posted by Ultimate_sig

Well i chose to stay with the 39 i know itll be fun

And it will be cheaper to shoot

[hoovco]

Originally Posted by Ultimate_sig

But if its chanber in .308 it can shoot the 51

Yep. My 308 loves M118LR NATO ammo.

[Ultimate_sig]

Originally Posted by MachineHead

And it will be cheaper to shoot

Well i ordered a vepr from a shop and they put it in the wrong box sp i called to fix it. They asked me if they put the wrong gun in the box or the gun in the wrong box. So they pretty much gave me a choice to fix it asking if i want 39 or .308

[austin92]

Originally Posted by robocop10mm

Wrong. I have heard a bunch of vets (primarily Vietnam era) state this. Absolutely NOT true. the NATO round is 12mm longer and will not fit in a typical AK. I think this "military legend" stems from the fact that Soviet artillery and morters are generally 1mm larger than US. It may be possible for them to use a US 81 mm morter in their 82 mm tube.


Nope, wrong again. The US loading of .308 is hotter than the NATO loading. It is the opposite of the .223/5.56 relationship

So none of the 7.62 rounds can be fired through a .308 and vise versa?

Could you go into a little more in to detail about the US loading and NATO load differences and what the 223/5.56 relationship is exactly?

[Ultimate_sig]

Originally Posted by austin92

So none of the 7.62 rounds can be fired through a .308 and vise versa?

Could you go into a little more in to detail about the US loading and NATO load differences and what the 223/5.56 relationship is exactly?

.308 is to 762x51 as is 5.56 to .223

[Jpyle]

Originally Posted by austin92

So none of the 7.62 rounds can be fired through a .308 and vise versa?

Could you go into a little more in to detail about the US loading and NATO load differences and what the 223/5.56 relationship is exactly?

With the 5.56/.223 rounds the caliber can be fired in the metric barrel, that is .223 can be fired through a 5.56 mm barrel but not the reverse. In contrast, a 7.62 x 51mm round can be fired through a .308 but not the reverse.

In regards to loads and pressures, all civilian ammo is loaded to SAAMI or some other international standard. Military loads may or may not conform to that standard so using a NATO round could be potentially dangerous in a chamber not specifically spec'd to handle higher pressure ammo.

[robocop10mm]

7.62 X 51 NATO looks like .308, but it is not the same. Pressures are lower on the NATO round. Dimensions are slightly different. You CAN shoot all the NATO ammo you want through a .308 rifle. No problems. You can shoot .308 through a NATO chambered rifle. You may have problems. Higher pressures can wear things out faster and MAY cause a failure of critical parts.

Really high performance .308 like the Hornaday Light Magnum ammo is a really bad idea in a NATO chambered rifle. Heavier bullets cause increased breach face thrust that can be a major isue to a NATO chambered rifle. Full load 180 gr .308 should never be shot through a NATO chambered rifle.

Many rifles patterned off miliary guns have very violent extraction/ejection. Commercial .308 brass may not be up to the task. NATO brass is thicker and tougher to tolerate the violence of the military designs.

Non gas operated guns like the HK-91 and CETME use fluted chambers. The flutes add to the stress. Case head separation is not at all uncommon wth .308 ammo in these guns.

Gas guns like the M1-A are not adjustable (as issued). Excessive pressures can bend things like operating rods.

Gas guns like the FN FAL are adjustable and can compensate for the different pressures.

The more I think about it one must also consider the pressure curve. When does the pressure peak? Most commercial .308 ammo uses slower burning stick type powder that peaks later than military spec ball propellant. That pressure curve allows port pressure to be higher as the gasses are still expanding at a high rate as the bullet passes the gas port. This is a bad thing. Just considering peak pressure is not good enough. It is peak pressure TIMING.

To get more to the specifics of the question; .308 is nominally 51 mm long. The "standard" AK round is 39 mm long. Thik of it like trying to get a .22 mag to fit in a .22 LR chamber, can't happen. The "other" Russian 7.62 is called 7.62 X 54r The case is 3mm longer than the .308 AND it has a rim (that is what the "r" stands for). The X 54r is also a much fatter, drastically tapered case. It, too, will not fit. nThe bullet diameters are different, too. Despite being called 7.62 mm, the bullets are different diameters. The US/NATO round uses a .308 bullet. The Russians use a .310-.312 bullet. The difference lies in the way the barrels are measured. Western nations generally use a measurement across the lands (smaller) and the Eastern bloc (Russians, Chinese) measure across the grooves. Copare it to measuring your car's dispacement by measuring the actual diameter of the cylider as opposed to measuring the diameter of the piston that rides in it. Same engine different dimensions or different engine, measure differently being called the same thing. Parts would not be interchangeable.

On to the .223/5.56 issue; Once again different dimensions (slightly). Much of the difference lies in the barrel. A 5.56 barrel has a chamber with significantly more leade. That is the throat. The tapered area between the neck of the case and the beginning of the rifling. Weatherby calls it "free bore". You can safely run up the powder charge because the pressures will not spike with the extended leade. You can get more velocity while keeping pressures manageable. A 5.56 round in a short throated .223 barrel can spike pressures beyond normal limits.

Some will claim the pressures are comparable. I disagree. SAAMI measures pressures at the mouth of the case. The Europeans measure pressure about 1.5" further down the barrel. Pressures are lower at that point. The 5.56 is proofed by European standards.

[Jpyle]

Please sticky that. It is the best, most concise explanation of this frequently asked question I have read in a long time.

Thanks for taking the time to post it Robo.

[austin92]

Yeah, I read it 3 times, thanks man