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What is a "Node"?

I think I know the strict meaning of a node (as an intersection of lines), but I'm curious about how the term is being used in the context of accurate shooting.

In some usages, the term seems to be synonymous with "optimal powder/charge/bullet combination.

What do you guys who use the term understand it to mean?
 
It's the idea that certain cartridge / bullet combinations have multiple velocities where accuracy is best and similar. Conversely, at velocities outside these nodes accuracy is degraded.

IMHO it's myth. Even if it's true, who cares? Any shooter will shoot the most accurate load at the highest velocity they can and stay in the pressure range they are willing to accept.
 
It's the idea that certain cartridge / bullet combinations have multiple velocities where accuracy is best and similar. Conversely, at velocities outside these nodes accuracy is degraded.

IMHO it's myth. Even if it's true, who cares? Any shooter will shoot the most accurate load at the highest velocity they can and stay in the pressure range they are willing to accept.

Some don't want to run their rifles at max velocities. Saves wear and tear on brass and is often not the most accurate load for your rifle.
 
A node to me is a flat spot in the rising trend line when you plot your powder ladder (powder charge increments) on one axis and distance from a common reference point on the other axis. This allows some "forgive" in your powder charge should you or your equipment not be as precise as you expect it to be.
CW
 
A node to me is a flat spot in the rising trend line when you plot your powder ladder (powder charge increments) on one axis and distance from a common reference point on the other axis. This allows some "forgive" in your powder charge should you or your equipment not be as precise as you expect it to be.
CW

Yep that is one kind of node. A wide range of powder charges with little vertical change.

Seating depth also has a node

And when you get them all working together you will find your.accuracy node.
 
I've always suspected that nodes are at least in part a result of fouling patterns because it involves groups and I seldom have trouble placing the first shot.
 
vibrations b.jpg
The figure shows vibration mode shapes of a cantilever beam – like a rifle barrel with the breach at the left end and the muzzle at the right. Consider this a snap-shot of the beam’s motion when the muzzle is at its farthest point from its undisturbed location (farthest from the horizontal line.) Mode 1 is the “fundamental” mode. Modes 2 and 3 are the first and second “harmonics.” The “nodes” are the points along the beam (barrel) that don’t move from their undisturbed position. When the beam is struck, all modes are set in motion, and the true shape will have the effect of these, and higher-order modes.
 
A node is where a multiple charge weights will shoot into the same group. The center of the node is usually very accurate. The node is a forgiving spot where minor differences in case capacity or charge weight will not cause a large degradation in accuracy. For instance, lets say that in my 6.5x47 39.8, 39.9 and 40.0 grains of a particular powder will all shoot into a 1/2" group and that 39.9 will hold a 3/8" group. With 39.9 as my selected charge weight, if I use a powder measure to load some rounds then I have a margin of error 0f */- 0.1 gr and still have accurate ammo. If I selected a charge weight that was very accurate but degraded with a 0.1 gr error then I would have to weigh each charge very carefully to maintain that accuracy. There are multiple tests you can run to find a node: ladder test, OCW test per Dan Newberry and the 10 round load development per Scott Saterlee. Each test has it pros and cons. Find the one you like best and use it. Don't forget that seating depth is part of the equation. Which to test for first: Seating depth or charge weight? Ask that question on any shooting/reloading forum and you will get very emphatic responses for both. I have been testing seating depth before testing charge weight. I will still test seating depth after finding a node as I have recently seen optimal seating depth change after finding the optimal charge weight.

FWIW,

Dennis
 
All mechanical systems vibrate. Large inputs of energy (like gunpowder) can produce larger vibrations, depending on the stiffness of the system.

Vibrating systems are more likely to be closer to the same every time if one tweaks the inputs so that they are close to nodes at the key moment. In a rifle, the key moment for accuracy is when the bullet leaves the barrel.

Reloaders don't worry too much about whether they are really on the barrel note that corresponds to the position of the barrel in time or the velocity of the barrel in time, but they really should be at the node of velocity as related to barrel whip (a vibrating cantilever) and at the minimum of the annular oscillations. (There are multiple modes of barrel vibration and movement. Different "nodes" are optimal for different modes of vibration.)

The experimental approach (what reloaders can quantify most easily), is to go for the smallest groups at a given powder charge with the least vertical dispersion with small changes in powder charge.
 
Some really good visualizations of barrel movement can be seen on Varmint Al's site. Google it if you're interested. He explores both the "standing wave" model and the "barrel whip," using a detailed finite element model of the rifle system. He does not yet add a stochastic bore time model to show the effect of load tuning upon group size.
 
"Stochastic"? I'll have to look that up.:eek:;) Not being a comp shooter, I work in the lower pressures to extend brass life. Mostly:cool:
 
Some really good visualizations of barrel movement can be seen on Varmint Al's site. Google it if you're interested. He explores both the "standing wave" model and the "barrel whip," using a detailed finite element model of the rifle system. He does not yet add a stochastic bore time model to show the effect of load tuning upon group size.

Someone might have put together a theoretical model of what barrel vibration might look like.

But this is a very complicated problem with way too many variables to reduce to a calculus equation.

Shooting that barrel and letting your target tell you what it likes will solve the problem
 
"Stochastic"? I'll have to look that up.:eek:;) Not being a comp shooter, I work in the lower pressures to extend brass life. Mostly:cool:

Stochastic
The term stochastic occurs in a wide variety of professional or academic fields to describe events or systems that are unpredictable due to the influence of a random variable. The word "stochastic" comes from the Greek word στόχος (stokhos, "aim").

What a great word...don't have a chance to use that one every day ;).
 
So, if I'm understanding this correctly (which might be assuming too much!), the goal is to have the barrel vibrating point when the bullet exits the barrel where it intersects with the straight line in Tiratore's helpful figure above in Post #12. This can be accomplished by variations in the powder charge and seating depth. The indication that you have accomplished this is that the group is small and unchanging in POI over small variations in both of these variables. Correct?
 
I think I know the strict meaning of a node (as an intersection of lines), but I'm curious about how the term is being used in the context of accurate shooting.

In some usages, the term seems to be synonymous with "optimal powder/charge/bullet combination.

What do you guys who use the term understand it to mean?

A node is a mythical place, like Shangri-La or El Dorado, where all dreams come true and everything is wonderful. Despite no evidence that such places exist, many still embrace the notion and spend their lives and fortunes seeking them.
 

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