What barrel profile has the best accuracy potential.

[amlevin]

Over the last year or so I've listened to some who say that "XXX" is the best "profile" for accuracy in a given caliber.

My question revolves around the .308 using a 175 gr bullet (SMK, TMK, or even 178 A-Max).

What profile, other than just a full diameter unlimited barrel, has the greatest potential for accuracy. A barrel with a "contour" similar to a Remington Sendero, an M-24 or just a straight taper. I've heard claims that those with "contours" rather than just straight tapers can be more accurate due to their ability to utilize the harmonics.

I realize this question may seem strange to some who might just say "go with the heaviest you can carry" but I'm more interested in whether there is any truth to the fact that a more "complex" barrel may be more accurate than just a straight piece of Stainless Steel with a rifled hole in it's middle.

 

['Freak]

Read these:

http://riflebarrels.com/what-makes-a-rifle-barrel-accurate/

“In another article on barrel stiffness, we outlined the mechanics and math behind barrel rigidity. The simplified version of that article is that a barrel too long for its diameter is not rigid. It can be whippy and accuracy will not be at its best. Generally speaking, a short and fat barrel is more accurate.”

http://riflebarrels.com/a-look-at-the-rigidity-of-benchrest-barrels/

 

[jlow]

BTW, the terminology here is incorrect - this is a common problem.

What you are asking is “precision” and not “accuracy”. A precise barrel will give consistent/tight groups. Accuracy means being able to hit a target you aim at, don’t think that is what is being discussed.

 

[Alex Wheeler]

Stiffer is not always better. I doubt you will see much difference in accuracy between contours. You will be able to fire more rounds with the heavier contour before heat effects your groups.

 

[ShootDots]

I would bet I have had chambered over 100 barrels in various calibers from .223 all the way to a .358 S.T.A. In all those barrels I have had 2 for sure and maybe 3, that would be considered R-E-A-L "hummers". One was a .257 Roberts A.I. , one was a 6.5 x 47 and the "possible" was a .308. They were all 26" with various contours. Two of them were Rock Creeks and one was a Krieger. It mattered not what you put down the bore, as far as projectiles were concerned, they all just hammered, with almost no tuning! I think you could have run stones down those barrels and they would have hammered!

Having said the above, I do not believe that contour or length (that is length within reason) has very much to do with the accuracy potential of a given barrel. How the barrel steel was made, drilled, rifling cut and straightness of the barrel has more to do with the potential for accuracy than contour does.

 

[amlevin]

BTW, the terminology here is incorrect - this is a common problem.

What you are asking is “precision” and not “accuracy”. A precise barrel will give consistent/tight groups. Accuracy means being able to hit a target you aim at, don’t think that is what is being discussed.

True. In colloquial use, accuracy and precision are synonymous. To be "scientifically correct" I probably should have used the term "precision". The "accuracy" is a function of the shooter 8)

 

[amlevin]

The simplified version of that article is that a barrel too long for its diameter is not rigid. It can be whippy and accuracy will not be at its best.

What now leads to a followup question. Is their a "golden ratio" of "caliber" to barrel length? I have a .308 with an effective barrel length of 21.88" (24" - CBTO of 2.118") which yields a length of 71 "calibers" (+/-).

My .223 has an effective barrel length of over 100 calibers. Both shoot sub .25 MOA.

Just curious if the "conversations" I've read about barrel lengths in "calibers" is really a factor or is it something more important for artillery pieces and "naval rifles".

 

[seymour fish]

Levin, On a subject we otherwise know little about, Women, the Golden ratio is 1:1.6. I am certain this may help. Seymour

 

['Freak]

The simplified version of that article is that a barrel too long for its diameter is not rigid. It can be whippy and accuracy will not be at its best.

What now leads to a followup question. Is their a "golden ratio" of "caliber" to barrel length? I have a .308 with an effective barrel length of 21.88" (24" - CBTO of 2.118") which yields a length of 71 "calibers" (+/-).

My .223 has an effective barrel length of over 100 calibers. Both shoot sub .25 MOA.

Just curious if the "conversations" I've read about barrel lengths in "calibers" is really a factor or is it something more important for artillery pieces and "naval rifles".

The two linked to articles and what’s within quotes up there is “Daniel Lilja” doing the talking, not me.

Folk go with longer barrels to get nearer to a full burn of the slower burn rate powders when they need the increased projectile velocity to have the things reach way on out there before slowing to too near the sonic transition. To offset the increased barrel whip that comes with the increase in the barrel’s length they’ll have to also increase the barrel’s diameter and so also its weight. The most capable .224” caliber rifle I’ve ever had opportunity to shoot had guessing a ~ 2” diameter cylinder somewhere between legal and 18” in length.

 

[amlevin]

The most capable .224” caliber rifle I’ve ever had opportunity to shoot had guessing a ~ 2” diameter cylinder somewhere between legal and 18” in length.

My .223(.224) has a 24" Bbl and is an MTU profile. Looks more like a piece of truck axle . Love shooting it as it literally stacks the bullets in the same hole at 100 yards. This rifle is heavy enough so I don't think I'll consider a 'no taper" barrel.

 

[jbhotrod]

Stiffer is not always better. I doubt you will see much difference in accuracy between contours. You will be able to fire more rounds with the heavier contour before heat effects your groups.

Think your answer is right here. A man named Harold Vaughn did all the testing you could possibly come up with regarding accuracy, though his book is quite expensive and rare nowadays. Still meaning to get ahold of a copy.

AFAIK, the results he came up with reflects the above; believe he tested all the way up to 3" diameter straight cylinder. Hell, some people have even done tensioned and water cooled barrels(and set records with them!!). That said, good barrels are found not bought. And diameter doesnt have much to do with the equation as long as its thick enough to not get too hot(and it tracks well). Stiffer does NOT mean better. If its too heavy, you aint gonna be able to tune it as good.
Look at BR results, theres plenty days when a light gun(s) outshoot heavy gun(s). Obviously the heavies will shoot better when looked at over the course of a season, but I would definitely surmise that the difference aint got nothing to do with contour/diameter. A hummer barrel is a hummer barrel, thats all there is to it at this point. Until Tony Boyer or someone else figures out what makes a hummer, you just gotta go with the hot brand at that particular time and say a prayer. And when they do figure it out, best believe theyll make a daggum fortune.

 

[jlow]

I think there are factors other than “precision” (not accuracy) that has not been discussed when considering barrel contours.

Assuming every other factor mentioned in the Lilja article is held constant (i.e. straightness of the hole, uniformity of the rifling geometry, twist rate, etc....) what barrel contour can affects is the width of your accuracy node.

The thicker the barrel, the stiffer the barrel, and the wider the accuracy node. That makes for a more forgiving rifle in terms of being slightly off in powder charge, differences in temperature, neck tension, etc. It does not necessarily make the rifle more precise but you will find those barrels tends to shoot just about most charges well and with less fliers.

 

[jbhotrod]

The thicker the barrel, the stiffer the barrel, and the wider the accuracy node. That makes for a more forgiving rifle in terms of being slightly off in powder charge, differences in temperature, neck tension, etc. It does not necessarily make the rifle more precise but you will find those barrels tends to shoot just about most charges well and with less fliers.

Are you certain of this? My thinking is a bit different here, and again this is all on paper and theoretical in nature without proper testing, but a longer or whippier/less stiff barrel will have the wider node, no? The reason I say this is fairly simple, thicker/shorter barrel means higher frequency vibrations, longer/whippier means lower frequency. With the lower frequency, consequently your muzzle will get more time at its preferred tuned location, right? This means wider nodes...right?
Correct me if my thinking is wrong here, just trying to look at things with a fresh perspective. And taking Mr Lilja's conclusions with a grain of salt. No offense to him at all, the man knows a lot about barrel making and much more about shooting than I do! But regarding his conclusions on stiffer = better, I dont think one can really say that. I believe the main reason for thick heavy barrels is heat and easier shooting/tracking.

There was a good discussion on this on the BR site a while ago, good info there.
http://benchrest.com/showthread.php?88106-Maximum-accurate-barrel-diameter-for-Heavy-Gun

Notice the importance stressed on barrel quality vs barrel diameter.

 

[jlow]

I am certainly no expert but my thinking is not frequency but amplitude. Heavier barrel has lower amplitude which means it will have a shorter “whipping/bending” distance which means narrower grouping due to the movement.

Think of it this way, when one is off an accuracy node, what happens is the bullet is exciting the crown when the tip of the barrel is still moving. The degree of that movement i.e. amplitude determines how far off course the bullet is moved.

 

['Freak]

When was a hummer of a pencil thin hunting barrel ever seen much less a record holder or winner in bench rest, either short or long?

 

[Alex Wheeler]

A stiffer barrel will generally have a narrower node window. It will have a higher frequency and lower amplitude. This means the nodes will be closer together and smaller. Either way you can tune it. I dont think you will run into a too stiff issue unless your using short barrels and barrel blocks with stiff stocks.

 

[gunsandgunsmithing]

A stiffer barrel will generally have a narrower node window. It will have a higher frequency and lower amplitude. This means the nodes will be closer together and smaller. Either way you can tune it. I dont think you will run into a too stiff issue unless your using short barrels and barrel blocks with stiff stocks.

We'll put. It's been my experience that more flexible barrels shoot bigger when out of tune than stiffer barrels...but both can be tuned to shoot small. Along with the lower frequency and higher amplitude of a less stiff barrel come longer duration at tuning nodes....hence wider tune windows. A mass at the end of the Barrel..aka a tuner...gives much the same effect and adjustability.

 

[jlow]

A stiffer barrel will generally have a narrower node window. It will have a higher frequency and lower amplitude. This means the nodes will be closer together and smaller. Either way you can tune it. I dont think you will run into a too stiff issue unless your using short barrels and barrel blocks with stiff stocks.

We'll put. It's been my experience that more flexible barrels shoot bigger when out of tune than stiffer barrels...but both can be tuned to shoot small. Along with the lower frequency and higher amplitude of a less stiff barrel come longer duration at tuning nodes....hence wider tune windows. A mass at the end of the Barrel..aka a tuner...gives much the same effect and adjustability.

I can certainly see higher frequency for a thicker stiffer barrel – not sure exactly what this does to the accuracy node but it would seem that the lower amplitude of a stiffer barrel should give a wider accuracy node as there should be less deflection when you are not directly on the absolute optimal powder charge?

 

[Alex Wheeler]

A stiffer barrel will generally have a narrower node window. It will have a higher frequency and lower amplitude. This means the nodes will be closer together and smaller. Either way you can tune it. I dont think you will run into a too stiff issue unless your using short barrels and barrel blocks with stiff stocks.

We'll put. It's been my experience that more flexible barrels shoot bigger when out of tune than stiffer barrels...but both can be tuned to shoot small. Along with the lower frequency and higher amplitude of a less stiff barrel come longer duration at tuning nodes....hence wider tune windows. A mass at the end of the Barrel..aka a tuner...gives much the same effect and adjustability.

I can certainly see higher frequency for a thicker stiffer barrel – not sure exactly what this does to the accuracy node but it would seem that the lower amplitude of a stiffer barrel should give a wider accuracy node as there should be less deflection when you are not directly on the absolute optimal powder charge?

I see what your saying, but with a high frequency we are having more cycles in a period of time so naturally we'll be at the end of each cycle for less time. But your partially right in that if we're out of tune, it wont be as bad on the stiffer barrel.

 

[jlow]

A stiffer barrel will generally have a narrower node window. It will have a higher frequency and lower amplitude. This means the nodes will be closer together and smaller. Either way you can tune it. I dont think you will run into a too stiff issue unless your using short barrels and barrel blocks with stiff stocks.

We'll put. It's been my experience that more flexible barrels shoot bigger when out of tune than stiffer barrels...but both can be tuned to shoot small. Along with the lower frequency and higher amplitude of a less stiff barrel come longer duration at tuning nodes....hence wider tune windows. A mass at the end of the Barrel..aka a tuner...gives much the same effect and adjustability.

I can certainly see higher frequency for a thicker stiffer barrel – not sure exactly what this does to the accuracy node but it would seem that the lower amplitude of a stiffer barrel should give a wider accuracy node as there should be less deflection when you are not directly on the absolute optimal powder charge?

I see what your saying, but with a high frequency we are having more cycles in a period of time so naturally we'll be at the end of each cycle for less time. But your partially right in that if we're out of tune, it wont be as bad on the stiffer barrel.

It all depends on what exactly “barrel time” is.

I personally do not think it is the low part of a cycle since if that was true, then there would be one for every set of up and down cycle and as we know this is not the case. Also as you said, if frequency goes up then the duration of that low cycle would shorten making it harder to hit the low spot.

My own guess is there are lots of “ringing” going on when a barrel fires since apart from the main cycle, there are also reflections like what one would see in a pond with limited diameter when one drops a rock into it. My own thinking is “barrel time” is certain time that when these cycles cancel out to cause a quiet period. However, amplitude still plays a role since if you are off that “barrel time”, you start to run into the “noise” and as such if the amplitude is lower; your group will open up but less so than if the amplitude is higher.