7.62 NATO vs .308 Win brass

[am44mag]

So, I have not been able to find a definitive answer on this. Is there really a difference in 7.62 NATO and .308 Win brass, or for all intents and purposes, are they the same? I've read claims that the 7.62 brass is thicker and will need to be downloaded, and I've read claims that the difference in thickness is negligible. The internet being what it is, people love to pass along myths and hearsay, so I was wondering what the truth is on this.

I have a pile of .308/7.62 brass and since this is not going to be for anything even resembling a precision rifle, I'm wondering if I should even bother sorting and separating the brass. I'm going to be reloading to 7.62 NATO specs, so I'm thinking that if I do my load development in 7.62 cases, the worse case scenario at that point would be the loads in the 308 cases having slightly less pressure and a slight POI change.

[Hickory]

If I remember correctly, and my memory has been hit & miss lately, the 7.62 is loaded at a slightly lower pressure than the 308.

[Winger Ed.]

In the old Sierra loading book, they said to reduce all their data by 1 grain to compensate for the thicker GI
brass, and its influence on case volume and pressure for the same charge in a civilian case.

They had this warning on all sections that covered popular sizes of GI rifle brass.
I never chronoed any to check if it made a difference or not- I just took their word for it.

Some other older manual had that too, but I forget which one it was.
Maybe the old Hornady book, but I'm not sure.

A quick way to maybe answer your question is to take a couple, size & trim, then weigh 'em.

[kungfustyle]

Yes, separate the brass, at least for me. I bought my first 308 about 5 years ago and got some 7.62 brass from a CB member. Wow, were they hard to get sized properly to chamber in my rifle. From data in Hodgdon's reloading I started showing signs of pressure two grains before max. I know some loads from Hodgon are over pressured, several threads on this on this site, so yes, sort your brass and start at the minimum and work up. Try your own tests, load a handful of each and fire them and see what you get. Now if you are going to shoot just cast with 5 or 6 grains of some pistol powder, I don't think it would make much difference.

[Smallbore]

I had the same experience.
Lots of Lake City GI brass that is around has been fired in machine guns. Lots of headspace.
Lake City Match brass is another story and is more consistent in weight. Mine goes 177 to 179 grains.
It still needs a reduction in powder.
Smallbore

[Neverhome]

Unless you do what Winger Ed says, everything else is just internet chatter. You could even take it a step farther and check volume with water. True measurements are the only way to prove what YOU have.

[Petrol & Powder]

OK, no internet lore here, personal experience from the mid 1990's.

I had commercial Winchester cases and Lake City cases side by side. After trimming and de-priming, I noticed the brass at the case mouth appeared thicker on the Lake City. I thought that must be some type of illusion, the difference in thickness isn't going to be great enough to actually see. So I put the casings on the scale. Sure enough, the Winchester cases weighed X and the LC cases weighed X + something.
The casings were identical externally but the LC brass was heavier.

Now, the difference wasn't huge but I would be cautious if I was loading at or near max levels with NATO brass. The flip side of that coin was the LC brass was heavier but it was also far more consistent in terms of weight. I have no idea why the commercial brass would vary in weight.

And as a side note, I agree with smallbore, A lot of that LC brass was fired in machineguns. Those cases were very bad on the first reloading cycle. They needed to be full length resized to chamber and until they were fire formed in my rifle's chamber, they weren't all that great. After that first cycle, and if confined to only one rifle - it was very good brass.

[30calflash]

Win brass was some of the lightest with more case capacity than others. It was preferred for long range shooting as more powder could be used safely. Win 308 brass weighed around 155 grains iirc.

Military brass meant for use in semi and full auto rifles had a thicker/stronger case head that made the capacity less than most commercial cases. Some LC late 60's match brass weighed 177-180 grains.

Recommendations I have read were to drop the powder charge .5 grain for every 5 grain increase in case weight. I believe the info was provided by the NRA when they had a technical staff.

[dragon813gt]

To the OP, check case capacity of the cases you have. Case weight and thickness don’t matter. It’s how much each case can hold. Capacity is easy to check.

[redhawk0]

size them...then weigh each. If the GI brass is heavier...it MUST be thicker. Reduced internal volume will require a slightly reduced powder load to achieve the same pressure.

If you're not shooting at Max....its probably not worth worrying about. I relegated all my GI brass for Lead only...I use commercial brass for hunting loads.

redhawk

[popper]

You are not going to run at full load so who cares. I use LC and Win/FC all the time in ar10, SIZED correctly, no problem. Sizing as chamber is slightly different! Results @ 50, near top load with ARComp 168gr Amax, ~40 rnds. Mixed HS, unknown # firings.
263817

[1hole]

Weighing cases only tells us how much metal each has, sized or unsized, as such, doesn't matter a bit when segregating cases by weight.

Actually, to be worth the trouble of weighing, the cases should first be uniformed. Trim-to lengths, mouths chamfered/deburred, necks reamed/turned, primer crimps removed and flash holes deburred. THEN we can learn how much our prepared cases actually weigh.

I can't believe that going from one case maker to another could cause a KABOOM unless it was already loaded to the ragged edge of loosing its togetherness. I reload but I don't run a hot-rod shop so military cases have never been a safety issue for me.

I believe the printed cautions about using GI cases are worth remembering but I suspect the real reason some manuals give those warnings is legal liability protection. No one wants to be sued by some dufus searching for reasons other than his own reloading screw-ups for blowing his rifle - plus a few fingers and eyes - from together. So, the company's lawyers (wisely) insist on a few legal boilerplate warnings that will hopefully sound good in some future tort court.

[Petrol & Powder]

"loosing its togetherness" - there's a phase I need to remember :-o

I've seen some engine blocks that "lost their togetherness" !

[ulav8r]

I have 46 or 47 308 loads in military cases. The 3 or 4 emptys have severely flattened primers and a bright spot where the ejector hole in the bolt is located. I foolishly used the same load I had been using in commercial brass. Had to hammer the bolt open. When I get time to get back to them, I will pull the bullets and reduce the powder charge.

[Drm50]

Many years ago I used a hypodermic syringe and checked volume of 7.62 vs 308 and 5.56 vs 223.
Both militaries had less case capacity due to heavier brass. I’m not crazy about loading military 5.56. But I load 7.62 match brass for my m70fw 308. I think you would have to be loading red line 308 in 7.62 cases to see any effect. I’ve been doing it for 50yrs. I shot 150gr for about 10yrs at around 2900fps. Then switched to 130gr at approx 3000fps and have had to problems with hundreds if not thousands of rounds.

[HangFireW8]

I don't full length size MG fired 7.62 LC brass. I set the shoulder back with a Redding body die, without the expander ball that causes so much case stretch and eccentricity, then treat it like normal fired brass.

How I treat normal fired brass is another topic.

I like LC brass, a tiny bit more efficient, and after extensive first time processing, and some culling, just as accurate in anything but a full up competition rifle.

[oconeedan]

Nobody mentioned, so I will...you will have to remove the primer crimp by reamer or swager on all military brass the first time you reload it.

[Wolverine19D]

Actually the 5.56 military brass will hold more powder then 223 brass on average. At least that is the case for Lake City 5.56 over standard 223 loads. But for 7.62x51 it is the opposite and the 308 brass has more case capacity. I have heard many people say to down load by 1-2 grn of powder.

Since I haven't actually loaded any 308 yet I am curious how much more velocity you can push from the 308 brass over 7.62 Nato brass? I figure some loads the NATO brass is pretty close to the same velocity with less powder but most of the time at max pressure the 308 brass will have a little more velocity? I'm mainly asking out of curiosity for building an AR10 for long range shooting where the velocity increase could be noticeable.

[am44mag]

I plan on loading to roughly M80 specs with either BL-C(2) or H4895. I have no reason to want to push this round hard, I have other guns that will do that far better. I think what I'll do is do my load development in the 7.62 cases and see how those loads perform in the 308 cases afterwards. If they're not to my liking, I'm keep the cases separated and work up a load for them that is close to the 7.62 load.

I just got a Lyman large primer pocket reamer in the mail, so that will make dealing with the 7.62 brass easier. I usually just chuck it up in my lathe and set the speed pretty low. I've done that before with 5.56, and I can go through a pile of brass pretty quick like that.

Thanks fellas.

[popper]

I processed ~ 150 308 Win/LC/FC yesterday. Neck on Win/Fc is just a tad shorter (LC is mixed year MG stuff). It will make NO difference unless you shoot really long range! I did ~moa @ 200 with HV cast, mixed brass, no weighing bullets. brass or trickling powder. Hodgdon shows 308W and 308Win service rifle(762 NATO?), notice the 308W just has a wider spread of charge. How much difference will there be for 92 vs 94% fill? Or 84 vs 82%? None unless you get close to 100%. Neck tension will make more difference! Load mixed, shoot and look at HS after the shot. You won't see a difference.

edit: 'service' rifle rating is by the Mil to make their rifles work (op rod operated) and cycle - reliability. Unless you are shooting service rifle (tanker rifle or or class competition), why worry? M80 pulls aren't that accurate anyway. You can always tinker with the load to get POI the same.

[Larry Gibson]

I plan on loading to roughly M80 specs with either BL-C(2) or H4895. I have no reason to want to push this round hard, I have other guns that will do that far better. I think what I'll do is do my load development in the 7.62 cases and see how those loads perform in the 308 cases afterwards. If they're not to my liking, I'm keep the cases separated and work up a load for them that is close to the 7.62 load.........Thanks fellas.

I've loaded thousand of M80 (U.S. spec) equivalent loads with both those powders and a couple others (H335 & AA2230). As popper says if the range to be used at is short then the differences in cases won't matter that much.

However, I do suggest sorting all the Winchester cases out if you are loading for a gas gun. The Winchester cases are considerably thinner than M80 cases in the web area and incipient case head separation can be a real problem. I also suggest the use of a standard 308W RCBS X-die to size the cases if used in a gas gun as case life will be considerably longer. Run a "search" for the test i did on them. I got 20+ loadings per case with LC brass using a M118SP load.

If you've a gas gun with a 22" barrel then you'll want 2750 fps with 145 - 150 gr bullets to duplicate U.S. M80 velocities. Also, with either of those powders with loads at that velocity the pressure will be fine.

[MostlyLeverGuns]

Weigh the brass. For 308/7.62x51 I've got Lapua at 178 gr, IMI - 180 gr, Peterson - 180 gr, Winchester - 159 gr, Frontier - 162 gr, IVI -180 gr, FX - 180, there are differences, various military usually run about 180 grain for me/my scale, all are averages of 10-15 cases, most vary plus minus a grain or two. Winchester is much lighter but they do vary. Weighing will tell you how it compares. Electronic scale works well for checking or sorting brass. I sort by headstamp, don't usually weigh every case, but do check 10-15 of each headstamp to avoid problems.

[Pirate69]

I thought I would take a look at the 308 Win/7.62 mm NATO case issue using QuickLoad. I have always heard the need to reduce the powder charge when using military cases and have taken the advice at face value. Guess, at this point, I need a better understanding as to why a charge reduction may be needed.

I selected at 308 Win load that is close to the SAAMI max and ran it through QuickLoad. The same charge was then run through QuickLoad as a 7.62 mm NATO load. The chamber pressure difference was very surprising.

So, with all things being equal, what is driving the significant difference is predicted chamber pressure? 59,752 psi compared to 72,398 psi seems to be significant. Note ion the table below, the NATO brass has 0.26 cc less case capacity than the commercial brass. It is assumed that this is a result of the “thicker” NATO brass when compared to commercial brass.

For this load, an 8.1% decrease in usable case capacity results in a 21.2% increase in chamber pressure. The decrease is only 0.26 cc. This is about 2 and ½ drops of water from a pipet; not a lot.

How much difference in weight of commercial and NATO brass is necessary to yield a 0.26 cc difference? Given that the SG of brass is about 8.5 grams/cc, it is calculated that a difference is the weight of the commercial and NATO brass is about 34 grains.

Is that a good number or is QuickLoad employing a safety factor? I just complete the resizing and trimming of both commercial and NATO brass. I pulled four commercial FC casts and four different NATO cases; one being a LC case. The FC cases weighed 175.4, 174.5, 177.4 and 177.3 grains. The NATO cases weighed 179.2, 172.0, 178.8 and 178.5 grains. Not a lot of difference in this small sample.

If you look at the extreme difference in weights between commercial and NATO cases, it is only 4.7 grains. This equates to only a 0.0358 cc difference in usable case capacity.

If the usable case capacity, for the 308 Win load, is decreased by 0.0358 cc, the pressure rises from 59, 752 psi to 61,210 psi.

I realize I am beating the data to get an answer and this is a limited sample of NATO and commercial cases. There may be cases with much different weight and that is baked into the QuickLoad software.

I think it is safe to say, that if using commercial cases only, the 308 Win data is appropriate. if using NATO cases only, the NATO data is appropriate. If using a mixture, a default to the NATO data is the safe bet.

Edited to add photo of chart. https://imgur.com/HTCLSkJ

Load: 168 grain Nosler CC. 46.0 grains IMR 4895



308 Win 7.62 mm NATO
COL 2.800 COL 2.800
CL 2.014 CL 2.014
Case Capacity 56 grains water 3.636 cc Case Capacity 52 grains water 3.373 cc
Usable Case Capacity 49.304 3.201 cc Usable Case Capacity 45.3 2.941 cc
Chamber Pressure 59,752 psi Chamber Pressure 72,398 psi

[Pirate69]

Win brass was some of the lightest with more case capacity than others. It was preferred for long range shooting as more powder could be used safely. Win 308 brass weighed around 155 grains iirc.

Military brass meant for use in semi and full auto rifles had a thicker/stronger case head that made the capacity less than most commercial cases. Some LC late 60's match brass weighed 177-180 grains.

Recommendations I have read were to drop the powder charge .5 grain for every 5 grain increase in case weight. I believe the info was provided by the NRA when they had a technical staff.

The 0.5 grain powder decrease per 5 grain increase in case weight caught my attention. I posted on a comparison of an identical load of 308 Win commercial brass pressure vs 7.62 mm NATO brass; as calculated by QuickLoad. QuickLoad does not indicate brass weights; only case volume. However, the difference in brass weights can be calculated (estimated) from the difference in case volumes. For the comparison that I did, the difference in case weights was 34 grains. Lets say 35 grains. From the rule of thumb that you posted, a reduction of 3.5 grains would be recommended to ensure a safe load.

I took the modeled output from the 7.62 mm load and reduced the powder charge until it equaled the pressure of the commercial brass. It took a 2.5 grain reduction in the powder charge to get equal chamber pressures for both loads. Looks the rule of thumb is a good one to remember. Hope I can remember it in the future.

[GONRA]

GONRA loaded quantities of 7.62x51mm NATO in LC 62 brass decades ago. Typical powder charges were in the 42 grain range.
IF I had used .308 Winchester brass, would have have ADDED about 2.5 grains powder based on lottsa previous load development.
Sounds like Pirate69's experience.....

[popper]

46.0 grains IMR 4895 WAY TOO HOT!

[Pirate69]

46.0 grains IMR 4895 WAY TOO HOT!

I agree 46.0 grains of IMR 4895 is a hot load in commercial cases; even more so in NATO cases. This load is not being recommended by any means. It was selected as part of a paper exercise since this load predicted a chamber pressure slightly below the 308 Win SAAMI. The objective was to see if NATO cases with this load would exceed the SAAMI; which it did. Again, this in not a recommendation for a load.

[303carbine]

So, I have not been able to find a definitive answer on this. Is there really a difference in 7.62 NATO and .308 Win brass, or for all intents and purposes, are they the same? I've read claims that the 7.62 brass is thicker and will need to be downloaded, and I've read claims that the difference in thickness is negligible. The internet being what it is, people love to pass along myths and hearsay, so I was wondering what the truth is on this.

I have a pile of .308/7.62 brass and since this is not going to be for anything even resembling a precision rifle, I'm wondering if I should even bother sorting and separating the brass. I'm going to be reloading to 7.62 NATO specs, so I'm thinking that if I do my load development in 7.62 cases, the worse case scenario at that point would be the loads in the 308 cases having slightly less pressure and a slight POI change.

Simply put, Nato brass is thicker, less internal volume , higher pressure loaded the same as commercial 308 brass.
Nato ammo is about 10 thou or so less in PSI for auto loading rifles, commercial 308 Win can damage internal parts of some rifle designs.
That's why the M1 Garand has its own loading data.

[AlaskaMike]

After reading through this thread, I have a question about an assumption that appears to have been made.

Several posts have commented on concluding that the mil brass is thicker because a mil case weighs more than a commercial case. How can we make that conclusion when we really don't know the brass alloy used in either the mil or commercial case?

Most of us here on the Castboolits forum are aware of how varying lead alloys can make a significant difference in bullet weight, despite the external bullet dimensions being identical. Why wouldn't we consider that with brass?

[beltfed]

A couple things from my years of Service Rifle competition with the M14 and M1A.
Back in "DCM" days, at Perry, we had to shoot the supplied M118 and Later the M852 white box ammo
In order to be able to practice get good zero's and shoot local matches, I developed a duplicate Handload that matched the
M852over my Oehler 33 chronograph: It was LC77 Match brass, Fed 210M primer, 41 gr IMR 4320 under 168 gr Sierra or Hornady BTHP match bullets.
( I had a couple of 20# kegs of the 4320, and it worked well, metered well(short stix))
One Important thing was, I used Forster's "308 National Match" die for full length sizing the brass. It is spec'd to exactly
bring the brass back to Mil Spec dimensions for the M14s. trimming as needed, of course.
The other important thing for the M1a/M14s was to set up the FL die for my particular rifle/Krieger barrel and chamber:
Take down the rifle, strip the bolt of the ejector plunger and extractor> Replace the Bolt Only in the receiver.
Then take a fired brass, and size it with the Forster FL die backed out a turn or so. Wipe off the lube and then drop the
case into the chamber with rifle horizontal and the bolt in Open position. Now you tip down the rifle, barrel down like
to a 45 degree angle or more until the bolt slided forward of its own weight. First try, the bolt will not close and lock itself.
Now resize the brass after turning the FL die a bit deeper into the press.
Do the bolt closing exercise again.
Repeat until the bolt will "just close" AND LOCK on the sized cast.
Now you lock that FL die ring and you have a die that will size enough, but not over re size the brass for that rifle.
Lastly, Yes, the Prison Range training brass I picked up from a friend whose brother was a guard, that was fired in M60s
was not very good. A good deal of it was stretched in the web and some would last only for one reload, even tho minimally
resized as per the above for my rifle. I got to "hooking" this brass to find and scrap those many that had incipient head separation
I finally tossed it all when I bought a couple of 20MM cans of new LC77Match brass.
beltfed/arnie

[HumptyDumpty]

I have noticed that most commercial brass has a far more prominent impression of my rifle's chamber flutes (PTR-91) after firing. Additionally, over the course of four or so reloadings, I had a neck finally split slightly. Again, this was commercial brass. I haven't been able to make a precise measurement, but I suspect that commercial 308 brass is generally thinner, or else, softer.

[303Guy]

After reading through this thread, I have a question about an assumption that appears to have been made.

Several posts have commented on concluding that the mil brass is thicker because a mil case weighs more than a commercial case. How can we make that conclusion when we really don't know the brass alloy used in either the mil or commercial case?

Most of us here on the Castboolits forum are aware of how varying lead alloys can make a significant difference in bullet weight, despite the external bullet dimensions being identical. Why wouldn't we consider that with brass?


Cartridge brass consists of approximately 70 percent copper and 30 percent zinc with no other alloying constituents.
Brass is a substitution alloy which means that zinc atoms replace copper atoms so differences in alloying percentages would be proportional to the difference in atomic weight. The difference in atomic weight is small at 3.33% so a change in alloy make up from 75:25 to 65:35 would produce a 0.34% increase in density. Not a lot.