Node !!

[cwood59]

I tiptoe into this discussion very lightly as I have been away from shooting on a regular basis for some time (but getting back into it). I admit, I am a YouTube junkie. However, it does provide, now and then, some useful information in these modern times. I have looked at a lot of videos from the Hornady Manufacturing channel. Quite often, they have a guest named Jeff Siewert. He is a ballistician, reportedly very well respected in his field. He wrote a book, Ammunition Demystified. I actually just got it from Amazon today. Just from thumbing through it, it appears to have the information that may shed some light on the OP's concern. I am an engineer by education/trade and am very fussy about the texts that I am willing to spend money on. I suspect this one is going to be a keeper. Absolutely no ties or affiliation, I just thought it looked worthwhile.

Sorry I didn't show up with more input or an answer.....still learning.

Curtis

 

[ronsatspokane]

I can easily see why two tubes cut from the same stock would behave differently. How well blended the steel is would impact how the gun drill bores the hole, how the tool creating the rifleing behaves (be it cut or button) and how the harmonics of a given charge are affected. These days the steel is usually well blended. I have only encountered 1 barrel that would not shoot at all. It looked good in the bore scope. It was from a well known barrel maker. It was the same contour, twist rate and length and "in theory" the same steel as the previous shot out barrel but it would not shoot as well as the shot out barrel. I replaced it with a budget screw on barrel and was back to shooting under 1/2 MOA. Never did figure out why that barrel would not shoot and I dumped a lot of money into different bullets, powders, primers, charge weights and seating depths. Perhaps chatter in the gun drill or rifling button/cutter? Most barrels I have installed in that caliber shoot the same load just as well as the previous barrel did when it was new.

As far as flat spots in velocity across a number of charge weights, never seen it. At increasing charge weights I have always seen an increase in velocity. That increase in velocity is not always linear but I've seen it for years using optical chronographs, Magnetospeed and labradar. I have not been able to correlate shrinking velocity gaps to a specific "optimal" load. Perhaps there is some correlation but I have not been diligent about connecting those particular dots. What I have found is that repeatable tight groups tend to repeat over the long haul so that is what I look for during load development. Only after I find that do I gather velocities, ES and SD info. In my opinion those tight repeatable groups are indicative of the fact that the load is in tune with the harmonics of the rifle. Some consider my approach to be that of a philistine. I wear that label proudly.

As far as testing different powders, primers, bullets and seating depths throughout a day, I don't buy what I'm being told is proof of optimal charge weights or ladder tests. I think we have all shot a given load at various points in a day (and even across strings) and seen different behaviors from that same load. I chock it up to subtle wind or atmospheric changes or maybe even the the increase in barrel fouling and perhaps all of the above. When the testing is at distance, we can leak a round out of the X ring or the 10 ring even between shots. And that leak can be vertical or horizontal. Again, not an indicator of load differences in my mind, simply a missed wind call. Again, a philistine by any other name.

 

[Straightshooter1]

I have no idea how the term "node" actually got started in the shooting circles. But I assumed it had something to do with the theory for barrel harmonics as harmonic sine waves have nodes and anti-nodes.

Because I've always had an insatiable curiosity to know how and why things work as they do, I try to understand internal ballistics. While I don't find it difficult to know the different of things at play, how they all interact to produce what we see or want. . . it's really complicated. As a shooter-reloader, it's really not necessary to understand the interaction and just rely on what I get on my targets. But my curiosity just doesn't let me leave it at that.

I'm convinced, until someone can better show me otherwise, that the barrel's harmonic node is what many of us are chasing after to get consistent small groups, whether we understand it or not. The clincher for me is how a barrel tuner works to tune a load. The last time I posted about this, gunsandgunsmithing has rightly pointed out to me an issue with this theory for the way the harmonics work on a cantilever. But think there's more to it than what he's referring to (for example, this). All the evidence simply points to the effect of a barrel's harmonic sine wave where the node is the most stable part and where the timing of the barrel time with the node produces the smallest variances. Still, one needs to keep in mind the complex dynamics of internal ballistics that are at play that can cause two barrels, that appear to be identical, may not perform exactly the same.

 

[Fast14riot]

An interesting take on the "node". Its not the barrel, but the load.

Why can there be some known loads for specific chamberings that just flat shoot, regardless of the barrel? FGMM is known to shoot better than most factory ammo in a wide variety of guns/barrels/rest configurations. Berger loaded ammo does too.

In hand loading, ~24gr RL15 or Varget under a 75-77gr in a LC case for 5.56 just flat shoots. ~30gr Varget under a 105-107 in a Lapua 6br case shoots. ~44gr H4831 under a 140gr bullet in nearly any brass in 260rem just shoots. In a good barrel any of these could be tuned a little better, but could also be taken out of tune a lot worse.

I don't think its any coincidence that many people end up nearly at the same end point in many chamberings (not all) and barrel combinations.

 

[Dave M.]

I think if Mr. Ezell was to comment, he would say the word “node” is a misnomer and that we should likely be referring to these spots as “anti-nodes”.
Dave

 

[Dave M.]

I have no idea how the term "node" actually got started in the shooting circles. But I assumed it had something to do with the theory for barrel harmonics as harmonic sine waves have nodes and anti-nodes.

Because I've always had an insatiable curiosity to know how and why things work as they do, I try to understand internal ballistics. While I don't find it difficult to know the different of things at play, how they all interact to produce what we see or want. . . it's really complicated. As a shooter-reloader, it's really not necessary to understand the interaction and just rely on what I get on my targets. But my curiosity just doesn't let me leave it at that.

I'm convinced, until someone can better show me otherwise, that the barrel's harmonic node is what many of us are chasing after to get consistent small groups, whether we understand it or not. The clincher for me is how a barrel tuner works to tune a load. The last time I posted about this, gunsandgunsmithing has rightly pointed out to me an issue with this theory for the way the harmonics work on a cantilever. But think there's more to it than what he's referring to (for example, this). All the evidence simply points to the effect of a barrel's harmonic sine wave where the node is the most stable part and where the timing of the barrel time with the node produces the smallest variances. Still, one needs to keep in mind the complex dynamics of internal ballistics that are at play that can cause two barrels, that appear to be identical, may not perform exactly the same.

View attachment 1469663

Lol. You beat me to it. Mike will be proud that we are listening and preaching the good word.

 

[ronsatspokane]

An interesting take on the "node". Its not the barrel, but the load.

Why can there be some known loads for specific chamberings that just flat shoot, regardless of the barrel? FGMM is known to shoot better than most factory ammo in a wide variety of guns/barrels/rest configurations. Berger loaded ammo does too.

In hand loading, ~24gr RL15 or Varget under a 75-77gr in a LC case for 5.56 just flat shoots. ~30gr Varget under a 105-107 in a Lapua 6br case shoots. ~44gr H4831 under a 140gr bullet in nearly any brass in 260rem just shoots. In a good barrel any of these could be tuned a little better, but could also be taken out of tune a lot worse.

I don't think its any coincidence that many people end up nearly at the same end point in many chamberings (not all) and barrel combinations.

So yeah, I hear what you are saying and have seen this first hand. However, the question arises, what does "just flat shoot" mean to any individual. What is the group size, what are the conditions, what distance are we talking about and on and on. Some calibers like the 6 BR and it's derivatives do appear to shoot in a variety of actions and barrels using a variety of powders, bullets and primers. Does that mean that a bad load cannot be found or a given rifle cannot shoot a common "known for accuracy" load? I think there are stereotypes and then there are the exceptions. Could it be that those calibers known to shoot well are usually chambered in higher quality actions and barrels? Don't know but it is something to think about.

 

[William Vogel]

Here’s what I do. I have a target velocity range that SHOULD be safe and I load 5 rounds each in charge steps of .2 grain increments. It’s usually 50 rounds. I start at the lowest charge and shoot groups with a chronograph for verification of velocity and group size on targets. I shoot 1 shot from each load, recording velocity and move through all loads. I then fire the second round through each load until I either find pressure, velocity or group size inadequacies. I once I find good results, I load another set of rounds of 10 each within a .1 grain difference. Maybe another 50 rounds or 30 rounds. Once I confirm the best, I then load another set of rounds with various seating depth to hone in even closer. I get lucky sometimes and don’t fire all the loaded rounds because once a trend starts, there’s no need to shoot the crap loads. The crap loads get the bullets pulled and the necks resized to make the final loads once optimal is found. Weather changes along with any other inconsistencies will cause variations in your results and must be taken into account but my go to loads shoot bugholes at 100 yards and shoot very nice at long range also. I promise this works and I have never found velocity plateaus once enough rounds have been fired. My velocities change with different weather and different weekends but the groups on paper stay consistent for the most part.

 

[Bottom Fodder]

So am I understanding this right when you find your “node” or what back in the day was called “sweet spot” then a slight plus or minus change in powder charge will not affect your accuracy basically giving you a little wiggle room

 

[JFrank]

So am I understanding this right when you find your “node” or what back in the day was called “sweet spot” then a slight plus or minus change in powder charge will not affect your accuracy basically giving you a little wiggle room

I’ll refer you to post # 21 ( correction post #19 ) as an example of that.

 

[Fast14riot]

So yeah, I hear what you are saying and have seen this first hand. However, the question arises, what does "just flat shoot" mean to any individual. What is the group size, what are the conditions, what distance are we talking about and on and on. Some calibers like the 6 BR and it's derivatives do appear to shoot in a variety of actions and barrels using a variety of powders, bullets and primers. Does that mean that a bad load cannot be found or a given rifle cannot shoot a common "known for accuracy" load? I think there are stereotypes and then there are the exceptions. Could it be that those calibers known to shoot well are usually chambered in higher quality actions and barrels? Don't know but it is something to think about.

Repeatable accuracy with a higher than average level of precision. 1/2 moa or better I feel is an acceptable number (especially if you have ever spent any time on a public range and have seen massive shot patterns people put down range).

Chamberings like 6br might be a little different as its basically hand load only, so you see it chambered in better than average equipment. However, 308, 5.56, 260rem, etc get cut into all kinds of rifles. I would think it safe to assume that if a person buys a factory rifle then tries to find a "node" with loading for it they will have to be above the average shooter and capable of seeing a difference in loads on target.

 

[praveen]

So am I understanding this right when you find your “node” or what back in the day was called “sweet spot” then a slight plus or minus change in powder charge will not affect your accuracy basically giving you a little wiggle room

So this was my original question. Why is there a little wiggle room around a sweet spot? Physically, that seems impossible to me and yet most of us (including me) accept this as gospel.

 

[Dave Way]

So this was my original question. Why is there a little wiggle room around a sweet spot? Physically, that seems impossible to me and yet most of us (including me) accept this as gospel.

Have you ever considered the effect that chamber pressure has on burn rate and efficiency?

Dave.

 

[DLT]

I am often amazed how we, as shooters, can take something so simple such a load development and cleaning a rifle and turn it into something mysteriously complicated.

When all you have had is trash like I have it is lol

 

[K22]

When all you have had is trash like I have it is lol

One man's trash is another's treasure.

 

[BoydAllen]

So this was my original question. Why is there a little wiggle room around a sweet spot? Physically, that seems impossible to me and yet most of us (including me) accept this as gospel.

In recent years I have made a hobby of trying to help shooters get better results. One fellow that I finally have given up on has always had a great deal of trouble accepting anything that does not fit within "it seems to me". The trouble is that what is logical to him does not work very well, and his rifle does not care about his "logic". My advice to everyone is to do well thought out experiments and to believe your targets. For most of us, the goal is to shoot better. With regard to your question. There will generally be more than one powder charge that works, but some nodes are wider than others. This is determined by experimentation. Other factors can influence node width. In the last few years tuners have come into more common use in competition, and some of those who use them tell us that they tend to broaden nodes, in that case, meaning that a given load will work through a broader temperature range. Often, we can only know that a thing works, but lack the proper equipment and or budget to prove why.

 

[Doom]

So this was my original question. Why is there a little wiggle room around a sweet spot? Physically, that seems impossible to me and yet most of us (including me) accept this as gospel.

I will give you the generally accepted explanation for the wiggle room from an engineering prospective. The rifle barrel behaves like a simply supported cantilever beam (if it's free floated) and any beam supported in that fashion will vibrate at its natural frequency when excited by a force. This can be a hammer strike or in the case of a barrel an internal explosion. The barrel vibrates in a sine wave function and if you look a a time wave function with time the displacement becomes small at the ends of the wave, so the barrel isn't moving as fast at those points.

Is this the only possible explanation? Probably not. But it does explain qualitatively what we see and it also explains the results we see with heavy barrels and tuners.

Have you ever considered the effect that chamber pressure has on burn rate and efficiency?

Dave.

If the question is about flat spots, for a flat spot to actually exist the burn rate and efficiency would have to change in one direction and then change back to the original or similar state. This type of behavior is is not something that happens. You are talking about something that is improving with load then suddenly stops improving and gets worse then starts improving again.

 

[praveen]

I will give you the generally accepted explanation for the wiggle room from an engineering prospective. The rifle barrel behaves like a simply supported cantilever beam (if it's free floated) and any beam supported in that fashion will vibrate at its natural frequency when excited by a force. This can be a hammer strike or in the case of a barrel an internal explosion. The barrel vibrates in a sine wave function and if you look a a time wave function with time the displacement becomes small at the ends of the wave, so the barrel isn't moving as fast at those points.
View attachment 1469763
Is this the only possible explanation? Probably not. But it does explain qualitatively what we see and it also explains the results we see with heavy barrels and tuners.


If the question is about flat spots, for a flat spot to actually exist the burn rate and efficiency would have to change in one direction and then change back to the original or similar state. This type of behavior is is not something that happens. You are talking about something that is improving with load then suddenly stops improving and gets worse then starts improving again.

So, in general the barrel vibrates not with its natural frequency but with a forced frequency that is forced by an external force. In this case, the contained explosion. Of course its more complex then this because the pressure is changing and there’ll be multiple waves at any given point of time. So, using this wave explanation, we can see that there are going to be times in a barrel’s vibration when it moving the least. But this will be true for every single powder charge and not a particular load. Doesn’t exactly explain why certain charges become a node. Possibly as explained at lot of places, in a ‘node’ or optimal charge, the bullet is exiting the barrel very close to when the barrel is experiencing its minimal vibration (peaks or troughs of the sine graph). Highly unlikely to happen given that there’ll be multiple waves but we do know barrels shoot better at certain charges.
Still, flat spots remain unexplained.
I’m beginning to see that maybe we are working with very small data sets. II’m going to try and run an experiment with my dasher. I do have a ‘node’ for it. So, I’m going to shoot a bunch of charges around that node to see if things remain flat on paper.
Also, if flat spots do exist and there’s a wiggle room around powder charges, why do we chase after better and better lab grade scales to weigh the powder charges?

 

[praveen]

Have you ever considered the effect that chamber pressure has on burn rate and efficiency?

Dave.

Hmm… not something I had considered. I would assume that as pressure increases, temp increases and the powders would burn faster.

 

[Bc'z]

Following along closely
All this takes place in just a fraction of a second, yet we see the results on paper.
WOW!!