Node !!

[Webster]

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?

You’re trying to analyze by considering things we don’t really understand and probably never will. I consider a node varying the powder charge and shooting 5 shot groups. If you have a big group then 2 small groups in a row, then a big group, then the node is in the area of the small groups. You will go crazy trying to understand why it happens. Just accept what you see on the target as real. No-one is trying to insult anyone here; they are all trying to help based on what they believe.

 

[Straightshooter1]

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?

There's not only the pressure wave acting on the barrel, but you've got the projectile, that's in contact with the barrel, moving through it and effecting the barrel harmonics as it moves. The incredible speed of all this happening makes the timing for the muzzles release of the projectile very critical. Whatever effects that timing effects what we're going to get on our targets. Those things than will make changes in the pressure wave will make changes in that timing as does the mass of the projectile and its surface contact with the barrel as it moves through the barrel. Though a powder charge may be consistent, things like ignition system and it's timing is also at play to effect some variation. It's a matter of getting all the elements working consistently and working together consistently.

Yes, when working with small data sets. . . like one shot ladders, it's going to produce things like a "flat spot" somewhere. The more shots taken, the more "flat spots" disappear into a linear line with ladder tests.

It seems to me that wiggle room around charges varies depending on the individual shooter's expectations. I just don't think there is a path to an absolute. ¯\_(ツ)_/¯

 

[CharlieNC]

Positive compensation is real, and provides for a flat point of impact vs charge weight response. The associated barrel vibration occurs at the speed of sound along the length of the barrel, not traditional transverse barrel vibration view. I presented a lengthy review about this last year with an absence of much discussion, which I had hoped would generate more opinions and insights. Seems it's a topic where speculation is more interesting than the grunt work of analysis.

 

[Mulligan]

Positive compensation is real, and provides for a flat point of impact vs charge weight response. The associated barrel vibration occurs at the speed of sound along the length of the barrel, not traditional transverse barrel vibration view. I presented a lengthy review about this last year with an absence of much discussion, which I had hoped would generate more opinions and insights. Seems it's a topic where speculation is more interesting than the grunt work of analysis.

Thank you for saying this out loud.

CW

 

[jimmymac]

I’m just a Pennsylvania hillbilly so I’m not smart enough to talk about flat spots and nodes associated with them.

I’m a score shooter. When I’m tuning my rifle I try to find a powder window that allows my rifle to perform well to give me a cushion. If I see that my tune is solid at 28.8 and test again at 29.2 with equally good results I’ll load at 29.0 and call it good. I will continue to test though as the match progresses. In my world this is my definition of a node.

 

[Bottom Fodder]

I’m just a Pennsylvania hillbilly so I’m not smart enough to talk about flat spots and nodes associated with them.

I’m a score shooter. When I’m tuning my rifle I try to find a powder window that allows my rifle to perform well to give me a cushion. If I see that my tune is solid at 28.8 and test again at 29.2 with equally good results I’ll load at 29.0 and call it good. I will continue to test though as the match progresses. In my world this is my definition of a node.

Sounds good to me

 

[chop house]

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.

thus NOT exhibiting monotinicity. to wit: of course, what if the rate of change (slope) varied in subtle ways, making flat spots appear to exist when working with only small samples sizes?

 

[Bottom Fodder]

So still learning. So if you had a gun that shot good with xx.02 of powder and it also shoot good with xx.06 grains of powder and you loaded 5 of each and shot all 10 would the 10 shots be a tight group or would they be two distinct groups

 

[jimmymac]

So still learning. So if you had a gun that shot good with xx.02 of powder and it also shoot good with xx.06 grains of powder and you loaded 5 of each and shot all 10 would the 10 shots be a tight group or would they be two distinct groups

It depends on if the two powder charges are printing to the same POI. It’s easy to test.

 

[ronsatspokane]

There's not only the pressure wave acting on the barrel, but you're got the projectile, that's in contact with the barrel, moving through it and effecting the barrel harmonics as it moves. The incredible speed of all this happening makes the timing for the muzzles release of the projectile very critical. Whatever effects that timing effects what we're going to get on our targets. Those things than will make changes in the pressure wave will make changes in that timing as does the mass of the projectile and its surface contact with the barrel as it moves through the barrel. Though a powder charge may be consistent, things like ignition system and it's timing is also at play to effect some variation. It's a matter of getting all the elements working consistently and working together consistently.

Yes, when working with small data sets. . . like one shot ladders, it's going to produce things like a "flat spot" somewhere. The more shots taken, the more "flat spots" disappear into a linear line with ladder tests.

It seems to me that wiggle room around charges varies depending on the individual shooter's expectations. I just don't think there is a path to an absolute. ¯\_(ツ)_/¯

That is something I've considered. Is it a sign wave or a radial wave (or the functional equivalent of given the definition of a radial wave)? When you think about it, as the bullet transits the barrel it is under considerable pressure. The forces associated with that pressure are pressing against the lands and generating rotational forces. They are, in effect, trying to unwind the barrel. Of course the barrel wins this fight due to its considerably greater mass and rigidity but still, the forces involved become anything but a simple sign wave.

Of course when a brake or a suppressor are involved the game changes. They add mass which dampens action much like a tuner but they do more. I had a 338 Lapua which had the gasses forced out at 90 degrees either side to vertical. Not down. You could see that barrel bend. But the bullet was gone by that time. One wonders though if the air being forced out of the barrel ahead of the bullet had a similar impact on the flex of that barrel that the expanding gasses did. It would require very expensive equipment to determine the truth of that.

 

[CNC-Dude]

OCW may work but I don't subscribe to it period.

The barrel question does pose a real question no doubt. In my mind even though those two barrels that were at some point joined and one solid piece I suppose something could have changed within the tooling, machinery, or operational in the process of the rifling stage within that 62 inches.

Erik Cortina has a recent podcast with Frank from Bartlien Barrels, and this topic of how two barrels cut from the same stick of material and machined identically at the same time, with the same reamer and identical in every way can have much different performance.....
He also has a podcast with the guy that first developed the OCW process and the guy that came up with the OBT(Optimal Barrel Timing)concept was conceived. All interesting discussions.....

 

[CharlieNC]

Thank you for saying this out loud.

CW

Clay there are several excellent technical references which demonstrate this, and the methods can be applied to further prove why increasing charge/velocity yields a flat or even falling poi. I applied this to my ladder targets and the proof was so convincing that I abandoned measuring barrel vibration. "The truth is out there Scully"

 

[gpoldblue]

thus NOT exhibiting monotinicity. to wit: View attachment 1469846 of course, what if the rate of change (slope) varied in subtle ways, making flat spots appear to exist when working with only small samples sizes?

I know one thing....if I'm going down the road in my car at say 60mph and mash the gas pedal and my car doesn't go faster and then I mash the gas pedal even further and my car doesn't get faster or actually slows down........I'd say my car has a serious problem!.......I guess I've hit some kind gas or velocity "node"......huh?

 

[gunsandgunsmithing]

Positive compensation is real, and provides for a flat point of impact vs charge weight response. The associated barrel vibration occurs at the speed of sound along the length of the barrel, not traditional transverse barrel vibration view. I presented a lengthy review about this last year with an absence of much discussion, which I had hoped would generate more opinions and insights. Seems it's a topic where speculation is more interesting than the grunt work of analysis.

Your work leading up to that didn't go unnoticed at all. It's still one of the better posts out there on what's going on. There's a lot happening in a short period but testing shows me that the tuner being at the end of the bbl does adjust for all those things and that "natural" frequency is still a big part of what we can control. It's repeatable and that says a mouthful in regard to all that's going on at once. If all those factors in fact over ride a "natural" frequency entirely, everything would have to be indentical with every shot and we know that's not the case, yet there is repeatability and that's what allows us to manipulate tune with a mass on the end of the bbl. At some point, we have to stop and analize what does happen vs why it does. There's a lot to be learned from that and I'm not sure there is any software available at this time to anylize every single force and cause for the end result in time that is happening but as long as it's predictable and repeatable, we can use it. I'm convinced that we have a good handle on tuners but from testing and vibration anaysis but there may always be some aspects that we can never measure. In simple terms, I look at it like this...the tuner being at the end of the bbl can and does adjust for the average of everything going on up to the point of bullet exit. If this were not the case, moving a tuner would seemingly only yield random results but we know that's not the case. All of those forces mentioned matter and that's why I think we still have much to learn, but the end result is still there. That alone has much merit and we are much closer to understanding how we can manipulate those forces repeatably than understanding the exact value of each force independently and their respective value to the end result...tune.

Thanks for your work!

I should add that "natural frequecy" in this context is not the same as if we simply tap on the bbl, but where all of these forces are going on, because those are the frequencies I had any interest in during testing. The rest of the equation opens up a whole different can of worms., entirely.

 

[Straightshooter1]

That is something I've considered. Is it a sign wave or a radial wave (or the functional equivalent of given the definition of a radial wave)? When you think about it, as the bullet transits the barrel it is under considerable pressure. The forces associated with that pressure are pressing against the lands and generating rotational forces. They are, in effect, trying to unwind the barrel. Of course the barrel wins this fight due to its considerably greater mass and rigidity but still, the forces involved become anything but a simple sign wave.

Of course when a brake or a suppressor are involved the game changes. They add mass which dampens action much like a tuner but they do more. I had a 338 Lapua which had the gasses forced out at 90 degrees either side to vertical. Not down. You could see that barrel bend. But the bullet was gone by that time. One wonders though if the air being forced out of the barrel ahead of the bullet had a similar impact on the flex of that barrel that the expanding gasses did. It would require very expensive equipment to determine the truth of that.

I visually perceive it more as a corkscrew sine wave.

 

[gpoldblue]

I visually perceive it more as a corkscrew sine wave.

I wonder if what you say is why 'clocking"of barrels on .22rf is sometimes done.
I visiually picture centerfire barrels oscillating more in an egg shaped pattern and not always straight up and down as we'd like to think.......maybe due to varying densities in the steel,thread joints,etc.

 

[gunsandgunsmithing]

I visually perceive it more as a corkscrew sine wave.

Why? I do too to a degree because I think there are both, but due to gravity, bbl movement and groups appear vertically biased(not only). I've posted several pics of targets on here. I can see where that applies to a degree based on the fact that groups don't form only in the vertical or in the horizontal, though. So I'm just wondering your logic is all. Not saying it's right or wrong, though. I think my tuner test shows a clear pic of what happens on the target but it can't possibly show every single force even if they are repeatable. Repeatable group shapes are undeniable if you see enough test targets. It's along the lines of 95+% of the time that the groups have the same shape patterns at different tuner mark intervals. That's freakin huge and I don't much care what anyone says. I see more test targets than possibly anyone because of how I do tuner sales. I only do them by phone, give very specific test instructions and I predict group shapes respective to tuner settings before the customer even shoots the test. That's only possible one way.

 

[ronsatspokane]

I visually perceive it more as a corkscrew sine wave.

The barrel is a noodle. More so than many realize. When the pointy end is pointing at the same location as the bullets exit, the groups are small. When it is not... well... we've all been there.

 

[Doom]

thus NOT exhibiting monotinicity. to wit: View attachment 1469846 of course, what if the rate of change (slope) varied in subtle ways, making flat spots appear to exist when working with only small samples sizes?

It is very difficult measure the differences between velocities for small increments, .2 grains in a 6.5CM. powder charge would expect to cause a variation approximately 10 to 12 fps. The best accuracy we have is probably the Labrador which is +/-2.7 fps. That is about 50% of the expected change. Throw in sampling variations and uncertainty for small sample sizes and flat spots occur due to noise and instrument uncertainty.

 

[Webster]

thus NOT exhibiting monotinicity. to wit: View attachment 1469846 of course, what if the rate of change (slope) varied in subtle ways, making flat spots appear to exist when working with only small samples sizes?

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

There seems to be an assumption that the barrel vibrates in a perfect classical vertical sinusoidal pattern. The barrel can be vibrating horizontally and vertically at the same time. Something like a figure 8 or much more complicated. Musical instruments have many harmonics and overtones imposed on the basic frequency.