Can we revisit the 308 vs. the 3-06 one more time? I swear it is a good question

I love this discussion. If I could respond to several points that were made in order to hopefully clarify what my thinking is.
I guess first I should mention that I am 100% behind the assumption that the –06 and the 308 will be the same for all practical attempts and purposes. i.e. holding less than a 2 inch group at approx 300 yards. I am really looking at the sub-MOA like a ¼ inch at 100 yards or even less. Ok that out of the way, labgrade, I get what you are saying about the consistency of each bullet. As an archer I REALLY know what you mean. And I understand how minute differences at “trigger pull” can have a big impact 100 or 200 yards downrange. It seems like what you are saying makes the difference is the ability to more completely fill the shorter case with powder. I did some looking at the case dimensions and the only practical difference is in the length of the case, the 30-06 being about a half inch longer. Unfortunately I don’t have my reloading book in front of me so I can’t tell you what the volume for different powders are (I really don’t want to search each one on the internet). I do know that an –06 does accept higher pressure. I also am going to assume that the ability to load to within say ¼ of an inch of the top of the brass (Arbitrary distance from the top, not an actual, practical distance) is just as possible with either cartridge. It would just require the right powder selection, right? That thinking (I admit I don’t know exactly what I’m talking about so it might very well be flawed...) would put them both right back into the equivalent cartridge realm.

Guyon and howardaw, for most of my life the fact that bench shooters all shot the 308 did speak volumes to me. However, as I started looking into things and critically thinking about the status quo I no longer find it to say anything at all. Let me explain. When the 308 first came out you are probably correct about the 30-06 being the favorite round. However, very clearly Winchester would have had a huge reason to try to make it’s new round the favorite. I would suspect that the massive improvements in accuracy that happened at the outset were not due to a superior round but rather some big steps forward in rifle design. I don’t know anybody that thinks a 308 is THAT much more accurate, rather we are talking about MOA vs. Sub MOA. Very tiny differences. Assuming that this is what happened once a few matches were won with the 308 then everybody started copying the winner. And it was a snowball from there. Now the roles are swapped as far as popular opinion go. In fact I suspect that 95+% of all bench shooters “know” that the 308 is more accurate because that is what they hear everywhere. There is the shorter round but I still don’t understand how that is more consistent than a longer case. It seems to just be the popular opinion. Now I am not saying that Winchester did this. And I certainly don’t think that even if they did, it was anything wrong, I am just saying I can very easily see how such a thing would come about.

I think I tend to agree with Gwehr98. How does a bullet moving the same know if it came from a “short squatty” cartridge or a “long skinny” one? I haven’t seen consistency tables, but I am sure they would be around somewhere if a 30-06 couldn’t be loaded within say 20 fps from round to round. I have never heard of the –06 velocity, rate of turn, or anything else varying greatly in hand loads. Does somebody have something they can point me towards that would show that?

I realize I am playing the devils advocate here. I am not trying to argue with everybody so as I come to your comments don’t take any of it personal. You could be right I just want to make sure and understand why. ;)
 
Q: How does a bullet moving the same know if it came from a “short squatty” cartridge or a “long skinny” one?

A: different barrel harmonics and internal ballistics
 
I am sure they would be around somewhere if a 30-06 couldn?t be loaded within say 20 fps from round to round.
Click to expand...

I don't know the answer, but it would probably be worthwhile to figure out just what kind of consistency is required for 1/4 MOA at 1000 yards, for example. 20 fps? 2 fps?

-z
 
Ric I see where you are coming from with the barrel harmonics, after all that is the whole concept behind the BOSS. However, if the exact same harmonics could be repeated then a rifle is accurate (or rather precise). How does the difference in cartridge length cause inconsistencies to the harmonics? Or put another way, how does a longer case with the exact same powder load and bullet from one round to the next cause variations in harmonics that are not caused when a shorter case is used?

Chad that’s the exact same article that Smithz supplied us with.

Smithz Excellent point! I honestly couldn’t tell you what sort of range in velocity or any other variables are acceptable to achieve sub MOA groups. Wouldn’t you suspect though that that information would be out there somewhere if the –06 really couldn’t be kept consistent? I would venture that with careful loading (even going so far as to load with optimal atmospheric conditions, or loading right before firing) both the -06 and the 308 could be kept to the same consistencies. I would bet less than 1 fps variations would be relatively easily attained. Somebody with more handloading experience and more time with a crono could probably say better than I could though...
 
Come July, I will have shooting the '06 for 51 years. In all that time, I have never had a clover-leaf group, whether three shots or five.

I have seen photos here at TFL from non-benchrest .308s that do show clover-leafs.

Leaving out all other cartridges, if I were going to do benchrest competitive shooting, I would choose the .308 over the '06. Given my "mechanic's attitude", I'm more interested in the results rather than the reasons for the results. :)

Pick your purpose, then pick your cartridge.

Fun, ain't it?

:), Art
 
Art that is the type of thing I was looking for. In your experience do you think you could say for sure that the rifle quality (or accuracy) wasn’t the factor in bigger group sizes with the –06? Generally speaking the 308 has a much better selection of accurate rifles than the –06 does. Most –06’s are “hunting” accurate rifles, not bench accurate rifles. For instance the Rem 700 (in bench rest versions) doesn’t even come in 30-06. Do you think that that is a factor here? It sounds like you are saying that the rifle selection isn’t the factor but I thought I’d ask...
 
ahenry, the .308 started out-doing the '06 in competition when it first came out, with equal technology in the rifles and bullets. So maybe the stiffer action is one factor, and more important than "better built". You'd have to have a bulkier, thicker receiver for the '06 in order to have equal stiffness. Since this sort of receiver was not available "back then", the .308 started winning the accuracy battle.

The short, fat, sharp-shouldered cartridges have become the choice in competition. Thus I believe that insofar as shape is a factor, the .308 is better than the '06 for that last little decrease in group size.

Overall, there is no one thing. It's a little bit of this, a smidgen of that, and you wind up with a total package which is better than other packages. Heck, even such tweaks as the seating of bullets close to the leade are relatively new. Add in the years of effort by hundreds or thousands of shooters to develop the most accurate loads, with the new powders. To get the '06 "up to speed" would take a lot of catch-up, and most folks won't bother--it's more trouble than it's worth unless you're just real hard-headed. :)

I'm just guessing and inferring from what I've seen and read. So much of it is art, not science, that it's hard to have absolute knowledge instead of educated guesses and beliefs.

Hope this is useful,

Art
 
Here's a slightly longer answer to the how does the bullet know if was fired from a fat case or skinny case.

The case, chamber and barrel make up a combustion and expansion chamber. Consider that the force accelerating the bullet is not a point source, but distributed over the area of the bullet base. Vortices and currents in the gases released as the powder burns will be different with different case lenghts - this makes a difference as to how the force is distributed. For a given caliber, some case shapes (length/diameter/shoulder angle) are more consistent in the way the accelerating force is distributed across the bullet base. More consistency = better accuracy.

The barrel harmonics will also be effected by case length. Obviously, harmonics will vary barrel to barrel. Each case length group will thus yield an ensemble of oscillation functions. If one case length yields an ensemble of functions that are "tighter", ie have less, then it is reasonable to predict that on average that case length is more accurate one. Again more consistency = better accuracy.

None of this is new. PPC cartridges were developed using these (and other) ideas. "Short and fat" has been shown time and again to be more consistent.

Remember also that we are speaking "statistically", and while we might predict that one case shape is more accurate than another the prediction only applies to a large sample, ie "on average". We cannot predict the behavior of an individual sample, there are just too many variables.

-ric
 
Still not convinced of the physics...

Ok, what all that states above is that you're looking for consistency, specifically in muzzle velocity, which is part of the internal ballistics equation. True, barrel harmonic nodes are ALWAYS a factor in a gun's given accuracy, regardless of the chambering and bore dimension. Hence all the work done with both free-floating and pressure-point bedding, as well as adjustable barrel harmonic dampeners (or Browning BOSS), even heavy weight vs. sporter contour barrels. You have to tune the load to match the barrel, or tune the barrel to match the load. Handloaders have known this for years. In it's favor, a .308's shorter bolt action, as opposed to a longer .30-06 bolt action, allows for less action flex or whip, too. I believe that ties into some of the system's harmonics, affecting accuracy. Another accuracy factor that's caliber-independent is a barrel crown that allows a uniform bullet departure without canting the bullet off to one side or another.

My point is that it makes not one bit of difference between the 7.62x51 (.308) vs. the 7.62x64 (.30-06) once the bullet leaves the muzzle, because at that very moment, the only forces acting upon the bullet's trajectory are the wind vector, drag of the bullet moving through the air, and gravity's downward pull. That .308 case can cause no more influence than can the .30-06, because combustion at that point is no longer relevant, the propellant gases are no longer a factor. The short, fat case or long, skinny case has done it's job of accelerating the bullet down the bore to a given pressure and velocity.

If you take the same care to build two different rifles, paying attention to details, including tuning the load to the rifle, or alternatively tuning the rifle to the load, I'll wager that with bore diameter and bullet weight being the same, you could make either rifle perform to the same degree of accuracy.

I'm very close to testing out this theory. I've got a proven 1/4 MOA target 6.5-06, based on the longer .30-06 case. I've got a spare action and 6.5mm Krieger barrel blank, as well as another Canjar trigger and target stock. My plan is to build a duplicate to the 6.5-06 rifle, but chamber it in either 6.5-284, or .260 Remington. The results, and comparison, should prove interesting.
 
If the 308 is more accurate than the '06...

whatever it is that makes it more accurate has to happen inside the gun, because once the bullet is in free flight it can't tell if it came from a 300 Savage or a 300 H&H, let alone a 308.
 
An interesting topic. I too am uneducated but in thinking about the differences between the two cartridges, it seems that the 06 with the longer powder column would provide more opportunity for variation in the powder burn. The primer ignites the powder directly adjacent and the burn moves forward through the powder column contained within the case. The shorter the powder column, the more consistent the burn and therefore more consistent harmonics and velocity. Don't know that this theory is true but seems to make sense at least to me.
 
Once again we have a bunch of interesting posts to mull over.
If there is a difference in accuracy of the caliber itself I think Art hit it on the head when he said it is a “little of this and a smidgen of that”. Unfortunately I think I fall into the category of hard headed. I love being able to do something (long range tack driving) in a way that falls out of the norm. Call me strange I guess. *grin*

Ric, I don’t think I buy what you are saying. I still don’t see how the exact same amount of powder from one round to the next in the exact same shaped brass from one round to the next can have such variations. These variations you speak of in harmonics and such seem to be things that affect one caliber to the next. Not things that are “more consistent” from round to round in the same caliber. Suppose you have do have a particular oscillation in the barrel when a certain amount of powder is used with a particular bullet and primer. In order for the –06 to be less inherently accurate that oscillation would have to vary from firing to firing even when powder, primer, bullet, brass, and everything else is exactly the same. Remember, achieving accurate groups is just exactly replicating what happened in the previous shot. To take the logic of “short and stubby equals more accuracy” to the extreme why don’t we see people shooting rounds that are as big around as dime but short like a 22lr (or something similar)?
Another reason I balk a bit at this is no other calibers seem to bear this concept out. If this were true I would expect to see rounds such as the 22 more accurate than the 223. Nothing bears that out. I think I m with Gewerh98, I just need to test both on equal guns. Anybody have one (in either caliber) they want to lend me? *grin*
When I conceptually think about what happens when firing a gun I can’t see length of the brass as an issue. Don’t forget that the powder gets all jumbled up before shooting. At the moment of firing the powder is not in a column in the normal sense of the word. It is stretched out with the air at the top side of the case, not the area near the bullet. If shorter calibers actually made a difference then wouldn’t we see more accurate groups either shooting uphill or downhill? I have never heard of the angle you are shooting at making a difference in group size (point of impact yes, group size no)
 
Gewehr98:

The second paragraph of your previous post is certainly true - the case can no longer influence trajectory once the bullet has left the bore. But you have ignored the possibility that the bullet's motion as it leaves the bore can have been influenced by the case.

Construct a "theoretical cartridge case/chamber/bore" that holds the bullet exactly aligned with the bore but when fired will apply all of the propelling force to a small area located at 12 O'clock on the bullet base. As the bullet leaves this case and traverses the freebore portion of the chamber, there will be a small force component that will pitch the bullet tip downward slightly. So as the bullet engages the rifling it is no longer perfectly aligned in the bore.

Upon leaving the muzzle the bullet is rapidly rotating. But the bullet is now also "corkscrewing" about its axis, a consequence of the bullet-bore misalignment. (Usually this is just called yawing, but i think that it is more correctly described as a combination of pitching and yawing.)

Now move that small area on the bullet base where the force has applied to a different spot and you get different yaw (interesting aside, for a perfectly concentric bore and uniform bullet you'd get the same yaw for any locations equadistant from the center of the bullet base). So here we have a variable that can affect accuracy.

This is obviously a deliberate exaggeration to make the point. But it seems to me that a difference in case shape will cause a difference in the way the accelerating force is distributed across the bullet base. This will cause bullet misalignment in the bore. I think it reasonble that for a given caliber, some case shapes will be more consistent in how that force is applied. And those case shapes will be capable of better accuracy.

ahenry:

"If shorter calibers actually made a difference then wouldn’t we see more accurate groups either shooting uphill or downhill? I have never heard of the angle you are shooting at making a difference in group size (point of impact yes, group size no)."

Well, actually angle does make a difference in group size. Tests made firing vertically up, vertically down, and horizontal. gave statistically significant variation in MV's based on orientation. These were military trials involving thousands of rounds of '06, IIRC. Variation in MV's would certainly make a difference in group size.

-ric
 
Other points:

ahenry:

"Remember, achieving accurate groups is just exactly replicating what happened in the previous shot."

On this we agree. But for the reasons i gave previously it is reasonable to me to think that some case shapes for a given caliber are more consistent in distributing the propelling force across the bullet base.

------------

"To take the logic of 'short and stubby equals more accuracy' to the extreme why don’t we see people shooting rounds that are as big around as dime but short like a 22lr (or something similar)?"

Look carefully at some of the BR and PPC rounds. They are about as fat and short as you can get to feed in existing actions.

-------------
"Another reason I balk a bit at this is no other calibers seem to bear this concept out. If this were true I would expect to see rounds such as the 22 more accurate than the 223."

I don't think rimfires vs centerfires is a fair comparison here. Rimfire ignition is quite complex. Remember that although the primer is arrayed somewhat uniformily around the circumference of the round it is only ignited at one point (or sometimes two places - Freedom Arms revolvers dual ignition system). And I think that we need to compare similiar power levels/pressure levels.

---------------
"I think I m with Gewerh98, I just need to test both on equal guns."

Sadly, a few paired tests would still not be enough to generate statistically significant results. There are other complications, for example the experimental design would also have to be "blind" so that the shooter should not know which case they are firing to eliminate unconscious bias.

That said i look forward to Gewehr98's 6.5 mm paired test results ! Then we can debate 6.5 '06 vs 6.5-08 (.260 Rem) !

This is a question that can be debated and tested endlessly. Talk and shoot, shoot and talk. You got to love it. Also note that i have not expressed an opinion as to which case .308 or '06 i think is inherently more accurate.

I agree with Art - Fun ain't it !

And since I'm afraid that if this thread goes on much longer i'll resort to Aggie jokes, i'd better leave it at that.

-ric
 
It's been tested!

Thousands of rounds manufactured on essentially identical equipment, test barrels made by the same people (10 or 20 or 30 barrels in each caliber, can't remember, all used at the same time).

Test groups fired at the same time on the same day at the same place. Like side-by-side test fixtures.

Groups fired all the way out to 600 yards, through multiple single-layer targets (200, 300 & 600, IIRC).

We're talking as statistically valid as it can be done. The bullets were identical, but were open base FMJBTs.

Yup, USGI Match ammo in .308 and .30-06. They even would fire the groups as fast as they could feed the test fixture actions, during lulls between slight breezes on very calm days. All ammo in later years made by the Lake City Army Ammunition Manufacturing Plant.

Theorize all you want about the reasons, but with the 173-gr FMJBT, the .308 was measurably, repeatably, and consistently accurate, IN 30-ROUND GROUPS.

I've read the reports of each year's Match ammo accuracy testing, as published at the time from 1959 to about 1967.

Now, any of you guys who brag about your three-round groups, just try to fire a full ten rounds (one target's worth) and see how much the group sizes grow.

When the barrels and ammo are at their best, the .308's slight accuracy edge has been confirmed with other bullets, most notably the Sierra Matchkings. You may find a SPECIMEN in .30-06 which will shoot tighter groups than another SPECIMEN in .308, but that will only mean that you have either a less-than-perfect .308 barrel, or your load is not matched to use the barrel's full capabilities.

By the way, statistical analysis of shooters' scores at the National Matches also proved a very strong positive correlation between caliber fired and scores recorded. This was true even comparing M-1s to each other (.30-06 vs .308).

Testing between only two rifles will *not* be conclusive. It's just that you have better odds of getting tiny groups with the more accurate cartridge.

BTW, velocity variation of less than 200 fps have far less of an influence on group size (200 yards and less, anyway) than will variations in exit gas action on the bullet base. That's why having a good crown is so critical to getting good accuracy.
 
Gee Whiz, folks!

The evidence is absolutely overwhelming that the .308 is more accurate than the 30.06. You don't have to understand it, though it would be nice to know. We have heard some of the theories. They have to be accumulative. The .308 IS the most accurate, though you can always use a particular rifle to prove any point you want. You have to accept facts. (Also, look at the PPC cartridges, and how their design has affected the competitive shooting. They are "more of the same", when comparing .308 design to 30.06 design).

The 30.06 is capable of greater ballistic performance. No one can argue that - it is a fact, too.

The .308 kicks less and is more fun to shoot. I own both and I CAN tell a difference. The difference, though, in recoil is not going to make or break your ability to shoot.

A short action rifle is superb, as compared to a long action rifle, when it comes to hunting. But if you need maximum bullet weight or velocity, you better give up that one nice little feature for that one nice little advantage.

Mike
 
I agree with Ron's point about the case and powder affecting the slight amount of wobble that is caused when the bullet spins slightly off it's axis. I've heard--I can't remember where--that some people will try to shake or tap their rifle while it is pointed in various safe directions so that the powder "settles" in a consistent pattern before shooting. This seems to me to be a little on the superstitious side, but do whatever floats your canoe--just do it safely.


I think the 30-06 cartridge looks better than the .308. Does that count for anything? :)

When dealing with so many variables that are difficult to measure and events that are difficult to observe, statistical analysis may be the only way to go. Apparently the statistics point to the .308 as being more accurate. This is only true under the conditions that people have been using these cartridges. If someone found a new way to load the 30-06, more statistical data should be gathered.

I wonder if more consistency in cartridges regarding power "settling" could be obtained by switching to caseless, solid propellant cartridges.

Oh well, all of this experimentation means more shooting and a rifle and cartridge that will be driven closer to perfection. I see nothing wrong with the continued rivalry between the 30-06 and the .308, as long as people spend as much time playing with the cartridges as they do BS'ing about them.
 
You must log in or register to reply here.
Back
Top