308 vs 7.62 Nato

[LDBennett]

The reference to my PTR-91 problem:

According PTR INC. (PTR-91 manufacuturer):

TAR LIKE SEALANT used in:
South African
Winchester white boxes marked 7.62
Venezuela Cavim
Austrian Hirtenberger
Some lots of German

In the PTR and H&K 91 variants the chamber is fluted to allow easy extraction of the cases against the roller lock action of these guns. In WWII and after, when the guns were developed originally, this fluting solved the hard extraction problem. The idea was that some of the gas pressure in the flutes of the chamber works against that in the case to minimize the hold the chamber has on the brass case. It normally works fine but the tar sealant goes into the flutes and coats the chamber wall making the chamber eventually stick to the cases, locking up the gun.

Would this happen in a bolt gun? I am not sure but it seems to me the pressure would expand the cases tightly against the chamber wall, locking out all the gasses from getting to the chamber wall at least initially. If the gun shows excessive blowback of the gases on the body of the outside of the case then the cases MAY get stuck to the chamber wall. But I don't think that would happen normally. It is my opinion that the tar sealnt would not effect the extraction of the cases from a bolt gun but indeed causes problem with extraction from the H&K 91 and its clones. We proved it through the use of South African ammo in a brand new PTR-91. Cleaning the chamber and changing to reloads eliminated the problem completely.

Broken extractors are usually associated with hard extraction often caused by excessive headspace (it says here ???). Or can be caused by rough chamber walls from corrosion from corrosively primed ammo usage in the life cycle of the gun. Smoothing the chamber with a drill motor and a stick wrapped in very fine sand paper, like 600 grit, often solves the problem IF you don't remove too much metal from the chamber walls to get the rust out. A smooth chamber aids extraction. Oiling the ammo cases can too but that makes the bolt work harder as the case friction is lost and the bolt has to take the full brunt of the pressure.

Finding the cause of extractor breakage is a process of eliminating the things correct with the gun only to end up with only the problem left.

LDBennett

[Joker18]

The big and major difference between 7.62X51mm NATO ammo and the .308 Win is the throat dimensions of the NATO 7.62 X 51 chambers are different and if my old memory serves me well the NATO chamber throats are deeper. Most current Milsurp ammo in 7.62X51 is loaded for military gas operated rifles and should be fine with any commercial bolt rifle chambered for .308 Win. The only exception is some of the 7.62 Indian surplus produced for belt fed machine guns that has been de-linked and sold as loose ammo. Some lots of that ammo was quite hot and are not recommended for M1A's and other gas operated military rifles.

[Vael]

Originally Posted by Popgunner

You would be safe to buy a rifle marked for .308 Winchester & fire 7.62 NATO ammo in it. 7.62x51 NATO ammo has a max pressure of 49,700 psi (usually called at 50,000 psi). SAMMI max pressure for the 308 Winchester was for years listed at 52,000 psi. Then that pressure max was raised to 62,000 psi.

Wrong.

308 Max Pressure - 62k PSI
7.62 NATO Max Pressure - 50k CUP ... or 60-61k PSI.

Originally Posted by Popgunner

Another thing to remember is that 7.62 NATO cases are THINNER than commercial brass-the opposite of the norm of military brass being thicker than commercial brass. Loads using NATO brass at max .308 Win levels should be reduced by at least 2 grains.

Wrong.

7.62 NATO brass is THICKER than 308 brass. Since they have nearly the same exterior dimensions and 7.62 brass is thicker, the levels are reduced by about 2 grains.



If you really want to know the difference between 7.62 NATO and 308, I would suggest reading this:
http://home.comcast.net/~ehorton/The...762%20NATO.pdf

Edit: For a short answer to if you can use 308 or 7.62nato in a rifle. I would say if you have a good quality rifle and good quality ammo, either should work fine. The main problems come mainly from severe out of spec exterior dimensions, not pressure. So if you have a tight tolerance, precise 308 rifle and you try to use some crap 7.62 from a 3rd world country, it might not work so well.

[Vael]

Originally Posted by gdmoody

I have a problem understanding something about this. A while back, I bought a Mossberg .308 rifle. At the same time I bought 50 rounds of surplus 7.62X51 NATO ammo. After I fired something like 6 rounds, the extractor busted. I sent it back to the factory where it was repaired. The second time, I fired something like 9 rounds when the extractor broke again, and again I returned it to the factory for repair. Second time back, I traded the rifle in for something else.

My friend who owns the gun shop, where I bought the Mossberg and the ammo, told me that he thought the problem was that the ammo was too "hot" to be fired in the .308 rifle. How can this be so if you are saying that 7.62 NATO can be fired in a .308 without any problems??

Ok, from my limited experience, I've noticed that most 308 companies download further away from their max compared to the military. For example, the 308 round at 62k psi max usually only gets loaded at 55k psi. The 7.62x51 nato round with a 60+k psi max will often get loaded to 58-60k psi. I think this is mainly to do with the 7.62 using thicker brass and being able to handle its max psi much better. So really, if you have a weak extractor and are running military 7.62, it might be too hot for your gun.


See above post for more information.

[Popgunner]

This is the link I posted here on TFF on loading blank cartridges where the guy stated 7.62 NATO cases are thinner than commercial cases. This may or may not be true in some types of NATO cases.
http://hubpages.com/hub/Making-Blanks-Part-2

This article has been done away with for unknown reasons.


vael: you seem to be setting yourself up as an expert in this area. Making statements such as:

"Ok, from my limited experience, I've noticed that most 308 companies download further away from their max compared to the military. For example, the 308 round at 62k psi max usually only gets loaded at 55k psi. The 7.62x51 nato round with a 60+k psi max will often get loaded to 58-60k psi. "

Was this limited experience you had that caused you to notice this phenomenon with any type of testing equipment? Maybe you just surfed the net & took as gospel what you saw written?

You & FAL Phill that wrote your article seem to think exactly the same. Are you two one in the same? FAL Phill seems to be arguing these points with many knowlegable folks on several gun forums.

The M-118 match load you use to say NATO ammo is in the 61k psi range is not regular 7.62 NATO ammo.

I'm just sayin'

[Vael]

Originally Posted by Popgunner

You & FAL Phill that wrote your article seem to think exactly the same. Are you two one in the same? FAL Phill seems to be arguing these points with many knowlegable folks on several gun forums.

I am not FAL Phill, I copied the link to his article from another forum discussing this same topic, and though it would be helpful to this discussionl. I think its strange that many forums that are stuck on the 7.62=50kpsi, mostly the ones with people that have less experience with firearms.

Originally Posted by Popgunner

The M-118 match load you use to say NATO ammo is in the 61k psi range is not regular 7.62 NATO ammo.

I never said anything about what ammo I use.


Honestly dude, if you want to know the answer, stop searching the forums and get some real data.

[jack404]

Hold on,

Australia makes 7.62 NATO but we make thin wall which is appoved

we are a net importer of 5.56 NATO and buy from the US NZ and i think Canada

and all are different slightly and i resize these before using them for reloads on my civilian same caliber rifles, i've based my civilian ones off available military stuff

but each nation is a tad different each factory even..

rule of thumb goes

for 7.62 civilian is hot stuff

for 5.56 Military is hot stuff

check all NON NATO compliant ammo for chamber pressures

( some south american stuff will knock your socks off)

even better, reload yourself , then you KNOW ..

[JLA]

Good info and advice Jack...