'99 Savage: .308 Win or 7.62 NATO?

Cheeky Munkey

Cheeky Munkey

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I'd always been led to believe .308 Win and 7.62 NATO were the same thing but I now have reason to believe otherwise. Don't have examples of each handy or I'd check myself.

Anyone with a micrometer and a pair of shells can tell me exactly what the difference is?

Other evening at the range a friend's Savage '99 in .308 Win failed repeatedly to eject spent surplus 7.62 cases while it passed factory .308 Win without issue.

Is this common? :confused:

tia,
Cheeky Munkey
 
I believe the shoulder angle is slightly different but dont quote me on that (I could be thinking .223 rem and 5.56x45 NATO). What violator said about the savage experiencing hi-pressures sounds correct to me.
 
Hope this helps on your question.


7.62x51mm NATO or 308 Winchester?
An Armourer Explains the Differences

Do you have a military surplus rifle chambered in 7.62 x 51mm? If so, I'll bet part of the reason you bought it was to get a "308 Winchester" at a really low price. Well, you screwed up. It's like looking at a Northern Pike and a Muskie. They're close yes, but each is distinctive, and you have to understand what you're looking at.

Early in my military career, I worked on the FNC1 rifle (7.62 NATO). For someone that had previously handled and fired only shotguns and hunting rifles, this was a real treat! Maybe being an armourer wasn't going to be that bad! It was only natural then, that curiousity would generate questions and comparisons about what I thought was the same cartridge - 308 Winchester and the 7.62x51mm NATO.


FNC1

As part of my personal battery, I had a Midland 2100 chambered for 308 Winchester. This rifle was made in England by a small company - Midland Rifle Co I believe - but owned by Parker Hale. Having lots of military 7.62x51mm rounds available, I shot them from my 2100 from time to time. There was never a problem chambering or firing the military stuff. It was a pleasant diversion over the long (read boring) periods spent at the range for base small arms qualifications.
(I traded it off some years ago for a Smith & Wesson Model 686. It's the only rifle I ever regret losing! - Steve)

Around this period I discovered that shooting reloaded cases fired from an FN was virtually impossible. They didn't want to chamber. My frustration led me to ask an older armourer what was wrong. In a nutshell, he told me that they probably didn't fit because they stretched. I was using a Lee Loader in 308 Winchester and didn't know that they only resized the neck, leaving the rest of the case untouched. The shoulders were blown forward on initial firing, so the case was simply too long to fit my rifle's chamber! Hmmm...
I tried the gauges from work in my own rifle. What a shock! None of them would fit! The corporal brought a set in from home and explained the difference. Here's what I discovered.

308 Winchester (SAAMI) Gauges Shop (Military) Gauges
GO - 1.6300" GO - 1.6350"
NOGO - 1.6340" NOGO - 1.6405"
FIELD - 1.6380" FIELD - 1.6455"

The gauge sets were different too! What gives? He told me that the dimensions of the two new and unfired cartridges were basically the same. The difference lay in two areas - chamber size and cartridge makeup.

Chamber Size
Look at the picture below. The top chamber represents a military rifle, the bottom one a commercial sporter. With many military rifles, their chambers can be significantly longer than, say, a Remington 700. Note that the military chamber would fail a NO GO check, but pass a FIELD check using the proper shop (military) gauges.

There is a .013" difference in chamber length however, between these two "Safe & Serviceable" rifles!
rimless2.JPG
 
Is it safe to shoot 308 Winchester in a rifle chambered for 7.62 NATO?

What about 7.62 in a 308?



By Jim Bullock

I have pressure tested thousands of rounds of ammo in many different calibers both professionally (years ago) and more recently using the facilities of the Canadian Gov't (Explosives Branch) and Expro (maker of IMR powder).

While I don't like sweeping statements, in 308/7.62 I have found that although the specifications have very similar maximum acceptable pressures, the military ammo is usually "hotter".

Commercial ammo tends to run a round 55,000 psi while I have seen some lots of military running around 60,000 psi. (Same pressure gun, observed in the same pressure testing project.)

Ammo specifications can be miss-leading. Military ammo is usually quoted using the CUP system whereas commercial ammo is quoted in psi. The actual pressure maximums are about the same, but the numbers are about 5,000 units apart. This can create the illusion that the military is lower pressure.

The military know what rifles the ammo will be used in and have a guarantee that the rifles will be in good shape. Commercial companies worry about lawsuits. There are rifles in poor condition, miss-matched bolts, unsuitable actions, etc. The last 50 feet per second will cost about 5,000 psi. As a commercial loader I would trade off 50 fps for the safety of 5,000 less pressure, any time. Although commercial ammo can be loaded to 60,000 psi the companies I have discussed this with tell me they don't like to go beyond 57,000 and 55,000 is what they prefer.

The military brass is heavier than commercial brass. I load 308 in commercial brass that weighs 157 grains. I load 7.62 in brass that weighs 195 grains. (I happen to have a large quantity of both types). Since the outside dimensions are the same, we know the internal capacity of the 7.62 case is less because of an extra 38 grains of brass. The powder capacity is very different and the pressure/velocity results of the two are so different I have to treat them as quite different calibers. The light brass can use a larger powder charge and obtain higher velocity at the same peak pressure. The peak pressure of a 308 and a 3006 are the same. The difference is powder capacity. More powder translates to more energy and more velocity. To a lesser extent, the same thing is true of 308 vs. 7.62

Commercial ammo seldom exploits the larger case capacity. In practice I find the military ammo loaded fairly "hot" and commercial ammo is less than max pressure.

Pressure being equal, the military brass offers a significant safety factor. Some actions have chambers with less head support than others, so a thick head is important.

When loading for 303 British the same thing is true about brass weight. Military brass is heavier. Segregate your brass, military vs. commercial and use 2 grains less powder in the military. If you load 3 to 5 grains less than the max powder charge shown in the book you will find the brass lasts much longer. 20 reloads instead of 3 to 5. Just neck size the first quarter inch of the neck, if it is to be shot again in the same rifle.

The suggestion about shooting over a chronograph is an interesting one. If the bullet weight is the same, higher velocity equates to higher pressure, but only if the brass is the same. As I have explained, 308 and 7.62 brass is not the same.

The Hornady Light Magnum ammo I have shot in 308 (both production and experimental) offers significantly higher velocity (around 200 fps) for ordinary pressures (around 55,000 psi). This is accomplished by using a very large charge of compressed slow ball powder. They stuff a 3006 load of slow ball powder into a 308 case. Don't try this at home. You can't do it.

In conclusion, commercial ammo probably has lower pressure than military. Military is safe if the rifle is in good shape. Hornady Light Magnum has unremarkable pressure and I would not hesitate to use it any rifle in good shape.

Handloading and down loading 100 to 200 fps is much easier on the rifle, the brass and the shoulder and is still perfectly fine for punching paper out to 600 yards (about 500 yards farther than is usually required.)



Jim Bullock

About the author:

Jim Bullock is the grandson and son of rifle shooting competitors. Jim started with a BB gun (a daisy pump) in 1950 and received his first .22 at age 10.

He has represented Canada twelve times as a member of the Canadian rifle Team as a shooter, Coach and Team Captain.

His fullbore rifle shooting started in 1960 using the Lee Enfield #4 in 303 caliber in what was known as Service Rifle (B). That was a well-tuned rifle with a Parker Hale 5C rear sight and the standard post front sight. SR (B) was deliberate (no snap, or rapid fire) at 200 to 1,000 yards. His best shot was a pair of bullseyes fired at 1,000 yards with a 26 minute wind change between shots (that is about 260 inches or about 21 feet of windchange).

He has an extensive firearm collection including a dozen or so Lee Enfields.
 
Thanks for that, V. Very informative. But I'm looking for definative information re. the dimensions of the two shells.

ie: Why did the .308 Win factory rounds pass seamlessly though the gun while the 7.62 NATO brass stuck/hung up in the chamber? The extractor didn't seem able to gain a purchase on the 7.62 casing and so ejection failed to occur.

I'm not sure I can see/understand how a marginal difference in power would cause this. Am I missing something?

Thanks for your help with this puzzle.

best,
Cheeky Munkey
 
Due to the shoulder on the 7.62 ammo being a bit farther forward, the case was getting slightly stuck in the chamber, and the extractor wouldn't let it get a good grip on it. Headsizes on the two are exactly the same. But 99's don't like to extract cart's that even seem like they are stuck. Les
 
Sounds like the same thing that was happening with my 99C in 284, I'd blame it on the pressures. Wheres the brass going when it's shot at those pressures? They gotta blow out and form to something. Either gonna go back or forward into the chamber deeper. The 284 wouldn't pull a shot casing out unless I really reefed on the lever which flew open about an inch after every shot. Smith said it might be headspace but I'm thinking not as none of the primers were backed out. I don't think they should have ever went to the Winchester calibers except for the 32-40, 38-55 and 25-35 anyways.
 
Violator22 said:
Is it safe to shoot 308 Winchester in a rifle chambered for 7.62 NATO?


Jim Bullock

About the author:

Jim Bullock is the grandson and son of rifle shooting competitors. Jim started with a BB gun (a daisy pump) in 1950 and received his first .22 at age 10.

He has represented Canada twelve times as a member of the Canadian rifle Team as a shooter, Coach and Team Captain.

His fullbore rifle shooting started in 1960 using the Lee Enfield #4 in 303 caliber in what was known as Service Rifle (B). That was a well-tuned rifle with a Parker Hale 5C rear sight and the standard post front sight. SR (B) was deliberate (no snap, or rapid fire) at 200 to 1,000 yards. His best shot was a pair of bullseyes fired at 1,000 yards with a 26 minute wind change between shots (that is about 260 inches or about 21 feet of windchange).

He has an extensive firearm collection including a dozen or so Lee Enfields.
Click to expand...

You forgot to mention that Jim won the Grand Agg in Bisley, is a member for the DCRA Shooting Hall of Fame and a member here on CGN.:p

Jim, care to jump in?
 
MadDog said:
I don't think they should have ever went to the Winchester calibers except for the 32-40, 38-55 and 25-35 anyways.
Click to expand...

MadDog,
Are you suggesting a '99 in .308 should be avoided?

Les,
As I read your posted articles, it's the chamber that's slightly larger (looser) on NATO military firearms, not the cartridge.

Does anyone have a micrometer and a .308 and 7.62 round handy can make a few quick measurements?

I'm really curious about this.

Thanks for all your feedback.

cheers,
Cheeky Munkey
 
Also notice that they cartridge is generally loaded to slightly higher pressures and cartridge thickness makes a big difference. the NATO case has thicker case walls that increase pressures more than the 308 case. Les
 
Sorry I'm azzbackwards. here it is, found what i was looking for.

They are NOT exactly alike although many people do treat them as interchangeable. You might get by in some firearms but the pressures are different and the shoulders are different. The difference in a bolt action will probably go by unnoticed. But in a semiauto firearm, trying to use a 7.62x51 in a modern firearm could cause chambering problems because the degree of angle on the shoulder of the 7.62x51 is not as great as on a .308. Using a .308 Winchester in a gun chambered for 7.62x51 could result in neck/shoulder splits and gas coming back at the shooter. While we're on the topic, .223 is not the same as 5.56 either...
 
Violator22 said:
Sorry I'm azzbackwards. here it is, found what i was looking for.

They are NOT exactly alike although many people do treat them as interchangeable. You might get by in some firearms but the pressures are different and the shoulders are different. The difference in a bolt action will probably go by unnoticed. But in a semiauto firearm, trying to use a 7.62x51 in a modern firearm could cause chambering problems because the degree of angle on the shoulder of the 7.62x51 is not as great as on a .308. Using a .308 Winchester in a gun chambered for 7.62x51 could result in neck/shoulder splits and gas coming back at the shooter. While we're on the topic, .223 is not the same as 5.56 either...
Click to expand...

7.62 Vs .308 and 5.56 Vs .223 comes up every few weeks. Not one has been able to point me to a thread on the WWW where a 7.62 fired in a .308 rifle or a 5.56 fired in a .223 rifle has had any KABOOM.

Speaking from a competitors point of view the Canadian rifle team takes .308 chambered rifles to Bisley England every year and shoot 7.62 RG ammo. When the CF switched to 5.56 just about every shooter had a .223 rifle built to shoot 5.56 ammo. I am talking hundreds of thousands of rounds without a KABOOM.

On the next point, can someone show me where I can buy 7.62 NATO or 5.56 NATO dies?
 
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