7.62 vs 308

[survivalshop]

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AMMUNITION, RELOADING

7.62X51 VS. .308 WIN.

SEPTEMBER 16, 2016 MIDSOUTH SHOOTERS 1 COMMENT

By Glen Zediker:

I hope by now that most folks do know there is a difference between 5.56 NATO and .223 Remington. Either way, I’ll be hitting that topic eventually, and the reason is because it really matters! NATO is loaded to much higher pressure than commercial .223 Rem. There’s up to 15,000 PSI difference. Reason: the NATO has a radically longer leade or throat, more room for expanding propellant gases.

If you are a handloader and are loading for a 7.62 NATO chamber, get a cartridge case headspace gage and subtract 0.004 inches from the spent case reading to use as a figure to set your sizing die (case shoulder set-back). Don’t take it down to .308 specs or it’s liable to break next use. Literally break. Here’s a spent case from my SAAMI-.308-Win. chamber (left) next to the same ammo run through a NATO. Whoa. Be aware that some commercial-spec .308 Win. ammo can literally come apart in a true NATO chamber.

But, what about 7.62 NATO compared to its civilian equivalent, .308 Winchester? Good question.

A little front-loading: There are industry standards for cartridge dimensions and operating pressures. SAAMI — Sporting Arms and Ammunition Manufacturer’s Institute — is a voluntarily-given base of information that defines and delineates our modern centerfire cartridges. Essentially, it’s an agreement among those in our industry to produce cases and cartridges and chambers that fit the specs, and they all agree to the specs. That’s for the U.S.A. SAAMI defines minimum and maximum headspace, for instance, and also chamber pressure maximums.

NATO—North Atlantic Treaty Organization—is the outfit that standardized mil-spec ammunition in use by the allies, including U.S. Armed Forces. It has its own set of standards for dimensions and outputs.

So. Comparing .308 Winchester and 7.62X51: .308 Win. came first. The two ended up differently… Like the 5.56/.223, the difference between commercial SAAMI-spec .308 Winchester and 7.62 NATO is in the chamber, but it’s in a different place. The difference in these two isn’t the throat, it’s the headspace. NATO is ridiculously longer. Although there are different pressure-testing standards used by NATO and SAAMI, .308 commercial is normally loaded to a higher pressure maximum than mil-spec NATO. It’s safe to shoot NATO rounds in a .308 Win. chamber. The difference comes in shooting a commercial .308 in a NATO chamber. At the least, the commercial case will be stressed, a whopping lot. Numbers?

Look for this to know it’s NATO. The cross-in-a-circle stamp identifies it absolutely.

Sho. SAAMI-spec headspace for a .308 Win. is a minimum (shortest allowable headspace or “GO” figure) of 1.630 inches, and a “reject” (too long) figure of 1.634. Well, the number given as a minimum for NATO is 1.638. The “reject” on NATO is 1.6455. I’m not at all clear on why anyone thought that was a good idea, but that’s what was done. It is also the reason that NATO cartridge case specs call for considerably thicker-walled brass. It has to endure that much more expansion. It’s a big reason not to purchase “surplus” 7.62 brass for reloading. Well that’s my advice… Cases fired through a true NATO chamber will be patently worthless to anyone owning a .308 Win. They’ll be blown beyond all reasonable repair.

A “true” NATO round will have a cross inside a circle stamped into the head. You can’t tell by chambering a round, no difference there. The other influential cartridge (not chamber) dimensions (overall round length, headspace, etc.) are patently the same for either standard. Crazy.

The preceding is a specially-adapted excerpt from the new book, “Top Grade Ammo,” by Glen Zediker. It’s soon to be available at BuyZedikerBooks.com or call 662-473-6107. You can also find Glen’s other works at Midsouth Shooters Supply’s.

[planeflyer21]

Don't see it mentioned above but the datum for measuring headspace is in different locations between 7.62x51 NATO and .308 Winchester.  The former is always at the top of the cartridge shoulder (2.015" from the base), the latter at a datum approximately halfway on the shoulder as measured from the base of the cartridge (1.5377"min/1.5477"max).

When the surplus Spanish CETMEs started being imported, a few purchasers blew them apart with commercial .308 Win ammo.

[survivalshop]

12 hours ago, planeflyer21 said:

When the surplus Spanish CETMEs started being imported, a few purchasers blew them apart with commercial .308 Win ammo.

  That was mostly because of Metallurgy, not to mention old worn out Actions  

     This comes up all the time , if you shoot any ammo out of a worn or over cut chamber , its dangerous . A lot of over sea's rifles , surplus , are like that , this is where this comes from . any modern rifle will shoot both ammo types , his assertion that the 308 case fired in a True 7.62x 51 chamber ( his words ) is ruined ( might be if shot from a well worn Chamber ), From almost forty years of shooting & hand loading from both chambers & ammo , I call that BS , period .  It may alter the reloading times with soft Brass , Remington Brass come to mind.

     Just because the 308 is listed by SAAMI spec's that it was tested & approved for the higher pressure , doesn't mean any are loaded to those max spec's .  The two Cartridges are the same , same exterior case spec's with a slight thicker web ( internally ) , they are identical , its the Chambers that are slightly different , of course you know that , as you have pointed out . 

     Of course if you have a surplus rifle , re-chambered for the 7.62x51( or a new Barreled ) , I really would not shoot 308 in it & would be worried about 7.62 Nato also . Old is Old & has probably met & surpassed its serviceable life , long ago .

     The Nato chamber was made to those spec's to have more room in the chamber for a rifle used in battlefield conditions where a chamber will get much more fouling then a hunting rifle will ever see , between cleanings . 

  I ask anyone to show me a set of 7.62x51 Sizing Dies .

  He may be referring to loading for Match ammo , in that I might agree with him somewhat with the fired cases , but thats a totally different ball game & I would be real picky about my Brass , in many ways . 
  
  These type articles , just get to me .

[jtallen83]

7 hours ago, survivalshop said:

  .  I ask anyone to show me a set of 7.62x51 Sizing Dies .

 

That has always been the tell for me. There are lots of statistics and opinions out there on this subject but the fact that only one die set is made for reloading has always assured me they are the same cartridge for my purposes. When reloading you always start low on the powder charge to the interior difference doesn't really matter then as long as you don't mix up the two types of brass. Chambers can vary between rifles with the same designation so used rifles should always be checked anyway.