2 brass .308 cartridge cases

7.62X51 vs. .308 Win.

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.

2 brass .308 cartridge cases
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?

NATO cross-in-a-circle stamp
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.

10 thoughts on “7.62X51 vs. .308 Win.”

  1. I’ve been loading and shooting 7.62X51 Military brass for years in my 308 bold rifles and have never had a case failure. Might have problems the other way, but I will continue loading and shooting milsurp 7.62X51 brass. I am also a very experienced reloader and consistently check my resized cases against a case gage.

  2. Hey guys I want to buy your book on reloading when will it be ready??? You write great stuff, please get er done & let me know.

  3. I usually don’t disagree but i have a person that works on the Small arms line at Lake City here in KC Mo. They load all there ammo on the same line to the same powder charge, be that LC or Federal for the average person. Yes the NATO round may produce a slightly higher pressure because of throat length but i have many 308 and 7.62 and 223 guns in my collection i have found no difference in chamber length and little in throat except for 5.56. Most of us have been shooting military rounds for years with no problem.Bob

    1. Just to make sure it was clear: there’s not really any difference in the ammo comparing 7.62 and .308. It’s in the rifle chamber, the headspace. With 5.56, the difference is in the chamber (longer throat) and also that the NATO is loaded to a higher pressure (because of the longer throat).

      1. Glen, thanks for the article. Question: Given the different headspace dimensions you site in your article, it should not be possible to chamber a 7.62×51 in a properly sized .308 WIN chamber. Is that correct or am I missing something.

  4. I was aware that military .308 brass was thicker than commercial brass but I didn’t know why until now. Lyman’s 47th. edition reloading manual advises against reloading military brass but says that if you insist, reduce maximum charges by two grains. I no longer have a .308 but I loaded & fired military brass in my Rem. bolt action .308 with no ill effects. I did not load any to max. charge levels. I was going to give the rounds I have left to a friend that has some type of military style .308 but since I don’t know what type of chamber it has, I don’t think I better do that. Maybe I will buy another .308 but since a hunter has no need to carry large quantities of ammo. around, I will probably just continue to load my .300 Win. to moderate velocity levels for less demanding applications.
    The only thing I know about a .223 is it makes a pretty good varmint rifle & is worthless for big game hunting.

    1. I don’t for the life of me know why NATO elected to make the chamber so long, when the ammo is “standard” .308 Win. Story: I eagerly accepted a Kroger-sack full of once-fired LC brass, 1100 rounds. 192 were re-usable in my M1A… That’s where the object in the photo came from. Reason I wrote this one is because there are a lot of “accepted” cautions about reloading mil-spec 7.62 and hope the reasons now are clear.

  5. This is nonsense. I have reloaded hundreds upon hundreds of once fired NATO brass (when I have to swage the pocket it’s a pretty good indicator that it has been fired once) without a single issue. The brass is USUALLY thicker than commercial, but not always. I parsed an enormous amount of 308 and 7.62 brass only last week, and have some lots of commercial that we more than the MIL stuff. It just depends, dudes.

    1. There is a lot of variation in mil-spec brass. Point is that it’s wise to be aware of the differences that can exist. I have encountered many many once-fired NATO cases that could never be reused in a commercial .308. It does just depend, and I agree. Just check out, though, before reusing mil cases.

  6. If there is any chance that a cartridge, could or would, be put into the firing chamber of a gun, that would cause any bodily injury because of any confusion regarding the size of the cartridge and how it fit into the firing chamber, every insurance company involved in providing insurance to a gun or ammunition manufacturer, would put a stop to it immediately. If you can dazzle them with brilliance, baffle them with BS.

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