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What determines the width of an accuracy node?

zfastmalibu said:
When you compare a straight tube with a HV most of the extra weight is on the muzzle end.

... which means nothing in this discussion.
 
"If you are comparing 26" barrels, the heavier one (e.i. the fatter one) that is "normally made, will ring at a lower frequency."



Another nit pic...wouldn't the wave lengths of a shorter/stiffer tube be shorter and closer together? Wouldn't that be considered a HIGHER frequency. That is how it is in the music world, not sure about the engineering world.
 
4xforfun said:
"If you are comparing 26" barrels, the heavier one (e.i. the fatter one) that is "normally made, will ring at a lower frequency."



Another nit pic...wouldn't the wave lengths of a shorter/stiffer tube be shorter and closer together? Wouldn't that be considered a HIGHER frequency. That is how it is in the music world, not sure about the engineering world.

You missed the operative phrase... "If you are comparing 26" barrels, " The comparison is barrels that are the same 26" length - there is no shorter one.
 
CatShooter said:
4xforfun said:
"If you are comparing 26" barrels, the heavier one (e.i. the fatter one) that is "normally made, will ring at a lower frequency."



Another nit pic...wouldn't the wave lengths of a shorter/stiffer tube be shorter and closer together? Wouldn't that be considered a HIGHER frequency. That is how it is in the music world, not sure about the engineering world.

You missed the operative phrase... "If you are comparing 26" barrels, " The comparison is barrels that are the same 26" length - there is no shorter one.


Man, you just love to be right. ;) You made a blanket statement which is just not true. "But barrels get stiffer by getting heavier" Twist it how you like, but thats not the case or how can a fluted barrel be stiffer than another barrel of same length and weight? I am done now.
 
I think deflection and stiffness are being confused here. Imagine a tapered barrel, threaded to fit a receiver at both ends. The same barrel will have the same stiffness regardless of which end is attached to the receiver, but certainly not the same deflection. Think reverse taper and think tuners.
 
zfastmalibu said:
CatShooter said:
4xforfun said:
"If you are comparing 26" barrels, the heavier one (e.i. the fatter one) that is "normally made, will ring at a lower frequency."



Another nit pic...wouldn't the wave lengths of a shorter/stiffer tube be shorter and closer together? Wouldn't that be considered a HIGHER frequency. That is how it is in the music world, not sure about the engineering world.

You missed the operative phrase... "If you are comparing 26" barrels, " The comparison is barrels that are the same 26" length - there is no shorter one.


Man, you just love to be right. ;) You made a blanket statement which is just not true. "But barrels get stiffer by getting heavier" Twist it how you like, but thats not the case or how can a fluted barrel be stiffer than another barrel of same length and weight? I am done now.

The statement was...

"If you are comparing 26" barrels, the heavier one (e.i. the fatter one) that is "normally made, will ring at a lower frequency."

I don't see anything about fluting or "stiffer"

If you need to go that far off track to "prove a point", you got a real whimpy point.
 
http://forum.accurateshooter.com/index.php?topic=3814361.1305

Look at the post from Jweb308. This is a prime example of a very wide node. Any charge he tested from 42.8 all the way to 44.2 looks good. Obviously he is a good shooter. I certainly wish any of my rifles had a node that large.
 
If you look at my OP you will see my comment on "groups posted on Eric’s thread", thus the question.
 
Im hoping this thread gets back on track as I find this very interesting. ( not the bickering, but the OP)

I have my own theory that follows close to what Chris Long believes based off what I have seen on target while doing ladder testing. Pretty interesting stuff that I may never understand but find it fascinating. In a recent test, I did a new load work up on a 280AI with a pencil #4 hunting barrel. Its nodes where a lot narrower and wilder between them than all my target rifles. I used up almost a whole 5feet of elevation going from a lower powder charge moving up 3 grains or 4 grains if memory serves me right. It was crazy in between the nodes that I saw. Just a 1/2 to 3/4 grain good node. So along the lines of the OP what makes it do that? Powder? Cartridge? barrel design? Bedding? Action?

Thanks in advance.
Russ T
 
CatShooter said:
CPorter said:
The load and bullet are like selecting different mallets to strike a bell.

Badd analogy cuz no matter what you hit the bell with, it rings with the same tone (frequency).

Same with barrels - the barrel vibrates with the same frequency unless you cut it - the reason changing the load improves things (or makes them worse) is that you change the time in the barrel, so you change the exit time in the vibration cycle.

And you win the Seegar!! ;D ;D
 
jlow said:

What determines the width of an accuracy node?

So this is a question for the real experts. I think we have all seen groups posted on Eric’s thread. The question is what determines the width of an accuracy node? Is it the rifle, the caliber, the load, or a combination of the three?

Post your response but it would be useful if it was backed up with some data.

First of all I am a newbie, not in the same league as zfastmalibu, CatShooter or many others here.

Having said that, I am a good reader and researcher. On the topic of barrel harmonics, it is my opinion that Chris Long http://www.the-long-family.com/ has made a seminal contribution to my understanding of barrel harmonics, his web site is a "must read".

Jlow, if you read Chris Long's paper he has lots of data. If you use his Optimal Barrel Time (OBT) and QuickLoad it will give you a clear target that will save you time and money. I put it to the test on my rifle and my friend's rifle, and sure enough it works.

I don't want to offend anyone but some have described the barrel "whipping", that is not accurate. Whipping would be true if the barrel was a rod, but the barrel being a tube reacts differently to the shock wave as it travels up and down its length on all sides. There may be some oscillation, but the critical fact is that the barrel acts very much like the old film camera shutters did. It constricts and expands as the sound wave travels through all sides of the barrel. I'm sure it isn't that simple because the bullet moving through the tube has to have an effect also.

Read Chris Longs OBT theory, it's all there.

Kindest regards,

Joe
 
Interesting discussion guys,
IMHO its the whole rifle/ load. Lock, stock, and barrel so to speak. Simple truth is that a rifle is a law unto itself . No two are alike. The accuracy node can be affected by many things. Not the least of which is the "mechanics" of the rifle . Bedding, mounting, optics mounting, scope tracking etc. Once these all are confirmed as good now you can load test. What you are trying to find is the bullet seating depth and velocity that the rifle likes no matter how long or thick the barrel is. You want to find where the bullet leaves the muzzle at the same point of barrel flex every time. As you test you may find many or just a few accuracy nodes both with seating depths and velocities. Use the one that gives you the velocity you need so the round gets to your target still supersonic if you're a target shooter (long range 1000yds plus) or if its a hunting round at least 1800 fps. In short the rifle is a tool. Find the "accuracy node" for what you will be using it for and testing is the only way. There is no magic answer that will apply to all rifles. My 2 cents.
Take care,
Phil Hoham
Berger Bullet Tech :)
 
In general, assuming the dominant component is the whipping motion of the barrel, and that a node straddles where the barrel reaches the limit of its reciprocating motion and reverses direction, I would venture to say that, all else being equal, a barrel with a larger amplitude of motion, and corresponding lower frequency of motion, will produce a "wider" node, but will also produce more vertical displacement of the groups' centers, and probably also larger groups around those centers, between the nodes.

Just my hunch, and perhaps obvious, but we're not dealing with pure sine waves here, there are always harmonics and random noise present.
 
brians356 said:
In general, assuming the dominant component is the whipping motion of the barrel, and that a node straddles where the barrel reaches the limit of its reciprocating motion and reverses direction, I would venture to say that, all else being equal, a barrel with a larger amplitude of motion, and corresponding lower frequency of motion, will produce a "wider" node, but will also produce more vertical displacement of the groups' centers, and probably also larger groups around those centers, between the nodes.

Just my hunch, and perhaps obvious, but we're not dealing with pure sine waves here, there are always harmonics and random noise present.
Good post! This is what tuners are for and is what they do, but with adjustability.
 

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