.308 vs. 7.62

[sqidd]

As some of you know I had some issues with my .308 POF the first time I shot it (there is another thread on this). I think I have everything all sorted and will be leaving here in a few to go test it out.

That being said someone sent me this a few minutes ago and I wanted to get the “collective take” on it.

Oddly enough I had no feed/stuck case issues with the .308 rounds I ran through the rifle and the 7.62 rounds were the ones that over pressured and blew out the primers and/or stuck cases. Just the opposite of what “should” have happened. If I'm reading the below correctly.

Are the .308 guys running both .308 and 7.62 with no issues in their semi auto’s? How about their POF’s.

Thanks a lot!

From link:

<span style="color: #000099">Before we go much further, we want to address the oft-posed question “are the .308 Winchester and 7.62×51 NATO one and the same.” The simple answer is no. There are differences in chamber specs and maximum pressures. The SAMMI/CIP maximum pressure for the .308 Win cartridge is 62,000 psi, while the 7.62×51 max is 50,000 psi. Also, the headspace is slightly different. The .308 Win “Go Gauge” is 1.630&#8243; vs. 1.635&#8243; for the 7.62×51. The .308&#8242;s “No-Go” dimension is 1.634&#8243; vs. 1.6405&#8243; for a 7.62×51 “No Go” gauge. That said, it is normally fine to shoot quality 7.62×51 NATO ammo in a gun chambered for the .308 Winchester (though not all NATO ammo is identical). Clint McKee of Fulton Armory notes: “[N]obody makes 7.62mm (NATO) ammo that isn’t to the .308 ‘headspace’ dimension spec. So 7.62mm ammo fits nicely into .308 chambers, as a rule.” You CAN encounter problems going the other way, however. A commercial .308 Win round can exceed the max rated pressure for the 7.62×51. So, you should avoid putting full-power .308 Win rounds into military surplus rifles that have been designed for 50,000 psi max.</span>

Link:
Link To Firearm Blog

 

[Parallax]

Re: .308 vs. 7.62

<span style="text-decoration: underline"><span style="font-weight: bold">.308 Winchester</span></span>

Case type - Rimless, Bottleneck
Bullet diameter - 0.308 in (7.8 mm)
Neck diameter - 0.3433 in (8.72 mm)
Shoulder diameter - 0.4539 in (11.53 mm)
Base diameter - 0.4709 in (11.96 mm)
Rim diameter - 0.4728 in (12.01 mm)
Rim thickness - 0.0539 in (1.37 mm)
Case length - 2.015 (51.18 mm)
Overall length - 2.800 (71.12 mm)
Case capacity - 56 gr H2O (3.64 cm³)
Rifling twist - 1 in 12 in (305 mm)
Primer type - Large Rifle
<span style="font-weight: bold">Maximum pressure (CIP Standard) - 62,000 psi (430 MPa)</span>

<span style="text-decoration: underline"><span style="font-weight: bold">7.62 x 51mm NATO</span></span>

Case type - Rimless, Bottleneck
Bullet diameter - 7.82 mm (0.308 in)
Neck diameter - 8.77 mm (0.345 in)
Shoulder diameter - 11.53 mm (0.454 in)
Base diameter - 11.94 mm (0.470 in)
Rim diameter - 12.01 mm (0.473 in)
Rim thickness - 1.27 mm (0.050 in)
Case length - 51.18 mm (2.015 in)
Overall length - 69.85 mm (2.750 in)
Primer type - Large Rifle
<span style="font-weight: bold">Maximum pressure(CIP Standard)- 60,200 psi (415 MPa) </span>

BTW both calibers are proofed at 125% of maximum pressure under CIP specifications... SAMMI doesn't test military ammo... most gun wags get the pressure figure for 7.62 x 51mm from a popular TM. The figures in the TM, according to many people I've spoken to are in error. Either in printing or through a misunderstanding of the difference between psi and cup the cup figure was used in error. CIP... which does test military ammo has the correct figure as listed above.

YMMV ... the controversy will continue I'm sure.... people like to pole vault over mouse turds.

 

[sqidd]

Re: .308 vs. 7.62

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Parallax</div><div class="ubbcode-body"><span style="text-decoration: underline"><span style="font-weight: bold">.308 Winchester</span></span>

Case type - Rimless, Bottleneck
Bullet diameter - 0.308 in (7.8 mm)
Neck diameter - 0.3433 in (8.72 mm)
Shoulder diameter - 0.4539 in (11.53 mm)
Base diameter - 0.4709 in (11.96 mm)
Rim diameter - 0.4728 in (12.01 mm)
Rim thickness - 0.0539 in (1.37 mm)
Case length - 2.015 (51.18 mm)
Overall length - 2.800 (71.12 mm)
Case capacity - 56 gr H2O (3.64 cm³)
Rifling twist - 1 in 12 in (305 mm)
Primer type - Large Rifle
<span style="font-weight: bold">Maximum pressure (CIP Standard) - 62,000 psi (430 MPa)</span>

<span style="text-decoration: underline"><span style="font-weight: bold">7.62 x 51mm NATO</span></span>

Case type - Rimless, Bottleneck
Bullet diameter - 7.82 mm (0.308 in)
Neck diameter - 8.77 mm (0.345 in)
Shoulder diameter - 11.53 mm (0.454 in)
Base diameter - 11.94 mm (0.470 in)
Rim diameter - 12.01 mm (0.473 in)
Rim thickness - 1.27 mm (0.050 in)
Case length - 51.18 mm (2.015 in)
Overall length - 69.85 mm (2.750 in)
Primer type - Large Rifle
<span style="font-weight: bold">Maximum pressure(CIP Standard)- 60,200 psi (415 MPa) </span>

BTW both calibers are proofed at 125% of maximum pressure under CIP specifications... SAMMI doesn't test military ammo... most gun wags get the pressure figure for 7.62 x 51mm from a popular TM. The figures in the TM, according to many people I've spoken to are in error. Either in printing or through a misunderstanding of the difference between psi and cup the cup figure was used in error. CIP... which does test military ammo has the correct figure as listed above.

YMMV ... the controversy will continue I'm sure.... people like to pole vault over mouse turds. </div></div>
If I am reading what you posted correctly it would seem that specific rifle aside the two rounds “should” be interchangeable.

Thanks

 

[kraigWY]

Re: .308 vs. 7.62

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">If I am reading what you posted correctly it would seem that specific rifle aside the two rounds “should” be interchangeable.</div></div>

They are to a point. It isn't the demensions that will get you, its how they are loaded. 7.62 Nato is designed for the most part, Semi-auto rifles. Meaning, to save wear and tear on the gas system, they are loaded with ligher bullets (=/< 175s) and medium burning powder.

Some 308 hunting ammo may be loaded with heavier bullets and slower burning powder.

Check you reloading manuels, some, like hornady have a special loading section for gas guns.

The problem is not unique to 7.62/308s. You have the same problems with the 30-06 in the Garand. Heavier bullets and slower burning powder will beat the crap out of the gas system.

If you're using bolt guns, you don't have that problem. Also in the case of the Garand, they have after market adjustable gas plugs witch will eleminate the problem.

This normally only affects hunting bullets, Match ammo, such as put out by Federal & Black Hills, load their ammo to match the M14/M1A, you'll find its damn near identical to M852 % M118LR so I realy doubt its gonna hurt your M1A or other gas guns.

The real problem is the "internet" is like the little games we played in grade school. You hear something, pass it around and by the time it gets back to you, its completely different.

We're (internet users) are no different. Someone puts out the information that "Heavy Hunting 308 loads are hard on the gas system of semis". By the time this information travels around the WWW, any thing resembling a 308 will turn your gas gun into a gernade.

 

[Sailormilan]

Re: .308 vs. 7.62

In the AMERICAN RIFLEMAN magazine a couple of years ago, there was short(1 - 2 paragraph) article on this. They stated that they had found Military Surplus 7.62x51 ammo that gave higher chamber pressures than commerciallyl made .308 Win ammo. However, they did not say what ammo it was that gave these results.

 

[sqidd]

Re: .308 vs. 7.62

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kraigWY</div><div class="ubbcode-body">The real problem is the "internet" is like the little games we played in grade school. You hear something, pass it around and by the time it gets back to you, its completely different.

We're (internet users) are no different. Someone puts out the information that "Heavy Hunting 308 loads are hard on the gas system of semis". By the time this information travels around the WWW, any thing resembling a 308 will turn your gas gun into a gernade.</div></div>

Too funny, and too right!

 

[sqidd]

Re: .308 vs. 7.62

I was just on the phone with Cody at POF about something else and he told me in the case of POF’s the chambers are dimensioned to eat anything you can throw at it. Of course at each end of the “load” spectrum it may not be the happiest rifle in the world but it should still run.

He said he runs Wolf through his guns! Say it ain’t so! If they can eat that stuff they should be able to eat anything short of rocks!

 

[FPO]

Re: .308 vs. 7.62

Thanks for the explanation, that's been bugging me.

 

[r0ttie1]

Re: .308 vs. 7.62

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sqidd</div><div class="ubbcode-body">I was just on the phone with Cody at POF about something else and he told me in the case of POF’s the chambers are dimensioned to eat anything you can throw at it. Of course at each end of the “load” spectrum it may not be the happiest rifle in the world but it should still run.

He said he runs Wolf through his guns! Say it ain’t so! If they can eat that stuff they should be able to eat anything short of rocks!

</div></div>

I've run Wolf through mine with no ill effects.

 

[redirt78]

Re: .308 vs. 7.62

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kraigWY</div><div class="ubbcode-body">Heavier bullets and slower burning powder will beat the crap out of the gas system...
If you're using bolt guns, you don't have that problem.
</div></div>

And what about piston guns like the OP's POF?

<span style="color: #000099">Edit</span>: I just read the post that says one of their employees says his "eats everything"... but will mine?..

 

[sqidd]

Re: .308 vs. 7.62

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: redirt78</div><div class="ubbcode-body">
And what about piston guns like the OP's POF?

<span style="color: #000099">Edit</span>: I just read the post that says one of their employees says his "eats everything"... but will mine?.. </div></div>
You could run the Superperformance if it was the end of the world and that is all you had. That is at the end of the spectrum though and it would not be too happy about it. I think the chances of having to run a round like the Superperformance is pretty slim though. You have to go out of your way to run that stuff. And why would you? It sounds like the POF's are happy with your average to "junk" rounds. Sounds good to me. I could run 93 octane in my truck, but it runs just as well on 89. So it gets 89.