Node !!

[praveen]

I know this topic has been beaten to death and I've read through a lot of discussion and articles around "What is a node?". I read through the concepts of 'whip' or a longitudinal 'donut' like wave traveling down the barrel when a round is fired. All that is okay. However, what is not clear to me is the generally accepted definition of node (using a ladder or OCW method) that seems to be the following:
"A node is where varying powder charges have little or no effect on the muzzle velocity and vertical shot dispersion on the target."

Now, this defies some basic logic for me. How could it be that you increase or decrease powder charge and the velocity remains almost constant. Why is that possible? Since pressure in the chamber/barrel is directly proportional to the powder charge and the pressure determines the muzzle velocity, the muzzle velocity must be directly proportional to powder charges too.
And if velocity is increasing with powder charges, there should be no point in the powder charge curve, where there's no vertical increase.

So, what's going on here? Why does the muzzle velocity and vertical dispersion on target become seemingly constant at whatever point we call a "node"?

This brings me another related question about "no two barrels are the same". If I have a say 62" long steel rod and two 30" barrels are cut out of it, chambered by the same reamer and put on the same action, they must be really close in how they behave. And I still hear a lot of talk about "barrel# 1 likes this load and barrel# 2 likes something completely different (sometimes a grain less of powder)". How could they be so different?

-Praveen

 

[Webster]

I know this topic has been beaten to death and I've read through a lot of discussion and articles around "What is a node?". I read through the concepts of 'whip' or a longitudinal 'donut' like wave traveling down the barrel when a round is fired. All that is okay. However, what is not clear to me is the generally accepted definition of node (using a ladder or OCW method) that seems to be the following:
"A node is where varying powder charges have little of no effect on the muzzle velocity and vertical shot dispersion on the target."

Now, this defies some basic logic for me. How could it be that you increase or decrease powder charge and the velocity remains almost constant. Why is that possible? Since pressure in the chamber/barrel is directly proportional to the powder charge and the pressure determines the muzzle velocity, the muzzle velocity must be directly proportional to powder charges too.
And if velocity is increasing with powder charges, there should be no point in the powder charge curve, where there's no vertical increase.

So, what's going on here? Why does the muzzle velocity and vertical dispersion on target become seemingly constant at whatever point we call a "node"?

This brings me another related question about "no two barrels are the same". If I have a say 62" long steel rod and two 30" barrels are cut out of it, chambered by the same reamer and put on the same action, they must be really close in how they behave. And I still hear a lot of talk about "barrel# 1 likes this load and barrel# 2 likes something completely different (sometimes a grain less of powder)". How could they be so different?

-Praveen

There are no flat spots. It's simply ignoring the fact that there is an ES. Plot 5 shots at each load. It looks a lot different. I go only by group size. It's good enough for shooting out to 400 yards plus at ground hogs.

 

[Ned Ludd]

I have no idea how the term "node" was propagated in reloading circles. I have always though its origin was related to precision/accuracy and derived from barrel harmonics; i.e. a vibrational "node". Regardless, it was in common use long before I started reloading years ago. The term "optimal window" is actually a much better descriptor of what we actually are looking for when we tune a load. Nonetheless, everyone knows exactly what is meant when someone says, "node", just like they know exactly what is meant when someone says, "neck tension", even though that's not technically correct, either.

I think it's also fair to state that many things people claim at reloading forums are opinions, nothing more. We, as reloaders, tend to be a slightly superstitious lot, and we sometimes do things that may not necessarily be based in hard science, simply because we perceive/believe that they work. We don't like to change things when they are working, at least in our minds. So certain approaches and/or beliefs may be shared and thus propagated, even though there may not be any rationale basis for them. I firmly believe that velocity "flat spots" fall into this category. As @praveen noted, I know of no scientific rationale to explain the existence of a flat spot in the velocity curve. Thus, I believe they manifest as the result of small sample size, not because there is actually a pause or flat spot in the velocity curve where velocity stops increasing in response to increasing charge weight. After all, combustion is a chemical reaction and chemical reactions simply don't behave like that. There can't be some limiting factor or reactant that creates a velocity flat spot, but then becomes non-limiting higher up the curve. Nonetheless, people are free to believe whatever they want.

FWIW - I have developed loads for .223 Rem and .308 Win loads for use in F-TR competition for years. During that time, I have gone through multiple barrels on multiple different rifles. There have been many occasions where I started the load development process from scratch with a new barrel and ended up at exactly the same load as with the previous barrel. In other words, the same charge weight and same seating depth yielded the same velocity [range] and the same precision over multiple barrels over a period of years. So it is absolutely possible for two barrels to behave similarly. However, I know people that have had certain barrels that tuned in much slower than expected for a given load. They shot well, they just didn't give the same velocity for tuned loads that were expected from running the same load in multiple barrels over some period of time. In fact, such an observation may easily be attributed to something such as differences in bore diameter, for example. Even though most other [external] dimensional aspects of two diffrerent barrels may be the same, nothing says that the bore and rifling can't vary from barrel to barrel. After all, manufacturing processes have tolerances. Even minor changes in something like bore diameter or how the lands were cut or formed could easily impact the load development process.

 

[davidjoe]

I’m going to suggest that some examples we are all familiar with may leave open some doors of truth on phenomena inside barrels that we can’t directly observe.

a) higher rpm, using more gas and air, will at some point actually produce less horsepower;

b) there is a speed we can slide a heavy refrigerator across a floor that is far easier than going any slower, or any faster;

c) it “may” be possible to reduce a log (also cellulose) to ash where it is converted to primarily cool smoke for a long period, instead of flame for a short period, with a greatly varying amount of total heat being released (because the smoke retains more chemical energy);

On the other hand, more air in a steel tank always equals more pressure, all other things being equal.

 

[praveen]

Guys give it a rest. I was hoping to hear something better than personal attacks.

 

[coldboreshot]

Let the show begin!

 

[Bill Norris]

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.

 

[bozo699]

I haven’t drank in years but I’m thinking I might crack a beer and watch the show
Wayne

 

[JEFFPPC]

I have had a pretty successful shooting career and I never looked for a node. I did not know what OCW was, never heard of a ladder. What I did learn by shooting lots of matches and talking to successful competitors and going thru lots of barrels was three things. "1, If you do all your barrels with your reamer with one smith your loads barrel to barrel will be extremely close. #2 Most important.....you need to develope a loading process that works for you. #3 Unless you can get back to back 3 or 4 shot groups in the zeros and low ones, keep working at it. Ok First free one....I have been using tuners for about 15 years, others use to laugh at me, I never found my load with one. I use them to keep my load in tune. Second free one......if you don't love your flags your in for a long ride. There are a lot more loading experts than good shooters.

 

[Bottom Fodder]

I remember back when a “node” was not a thing and now it”s “ the thing”

 

[K22]

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.

 

[Acyr]

Bore diameters do vary. Groove diameters can vary even more. I believe this is a big reason why two barrels from the same lot, chambered with the same reamer don't always shoot the same. Speed or accuracy wise.
Think about it. If one 30 cal barrel has a groove diameter of .3080 but the next one ended up at .03085 (still within sammi spec) How much extra internal volume does the larger groove 30" barrel have compared to the .3080 barrel?
.

 

[praveen]

Bore diameters do vary. Groove diameters can vary even more. I believe this is a big reason why two barrels from the same lot, chambered with the same reamer don't always shoot the same. Speed or accuracy wise.
Think about it. If one 30 cal barrel has a groove diameter of .3080 but the next one ended up at .03085 (still within sammi spec) How much extra internal volume does the larger groove 30" barrel have compared to the .3080 barrel?
.

I agree with this part that two barrels made from the same steel bar could be bored differently.

 

[Acyr]

In cut rifling it all depends on who is running the rifler. How consistent they are at measuring to the tenth. Whether or not they are paying attention, hung over, etc. LOL

 

[BoydAllen]

I know this topic has been beaten to death and I've read through a lot of discussion and articles around "What is a node?". I read through the concepts of 'whip' or a longitudinal 'donut' like wave traveling down the barrel when a round is fired. All that is okay. However, what is not clear to me is the generally accepted definition of node (using a ladder or OCW method) that seems to be the following:
"A node is where varying powder charges have little or no effect on the muzzle velocity and vertical shot dispersion on the target."

Now, this defies some basic logic for me. How could it be that you increase or decrease powder charge and the velocity remains almost constant. Why is that possible? Since pressure in the chamber/barrel is directly proportional to the powder charge and the pressure determines the muzzle velocity, the muzzle velocity must be directly proportional to powder charges too.
And if velocity is increasing with powder charges, there should be no point in the powder charge curve, where there's no vertical increase.

So, what's going on here? Why does the muzzle velocity and vertical dispersion on target become seemingly constant at whatever point we call a "node"?

This brings me another related question about "no two barrels are the same". If I have a say 62" long steel rod and two 30" barrels are cut out of it, chambered by the same reamer and put on the same action, they must be really close in how they behave. And I still hear a lot of talk about "barrel# 1 likes this load and barrel# 2 likes something completely different (sometimes a grain less of powder)". How could they be so different?

-Praveen

Despite representations to the contrary, often we only know what happens when we do a thing, but not why it happens. One thing for sure, compared to your understanding, targets are a lot more important if we are primarily concerned about results.

When I try a new powder that I believe has potential for my PPC, my first task it to do a test that tells me what the charge weight limit is, based on pressure signs and which tells me if and what adjacent charges print close on the target. I do this, on a morning when the wind is kind, over flags, shooting single charges at the same target, trying to find the same condition for all, with a charge increment of .3gr. Most of the time I will see a couple of clusters that indicate a suitable charge weight node is probably at their average or middle charge. Further testing usually confirms this. This is just a starting point. I use a seating depth that has worked well in the past, perhaps .008 or so into the rifling.

 

[Mulligan]

How much flatter can it get?



Shot at 600 yards
6 dasher


Same gun same day, different powder.
Flat spots are REAL!

Believe what you want, and I’ll keep tuning like I do.
CW

 

[coldboreshot]

In cut rifling it all depends on who is running the rifler. How consistent they are at measuring to the tenth. Whether or not they are paying attention, hung over, etc. LOL

I think I ended up with a couple of those over the years. Lol.

 

[jackieschmidt]

I know this topic has been beaten to death and I've read through a lot of discussion and articles around "What is a node?". I read through the concepts of 'whip' or a longitudinal 'donut' like wave traveling down the barrel when a round is fired. All that is okay. However, what is not clear to me is the generally accepted definition of node (using a ladder or OCW method) that seems to be the following:
"A node is where varying powder charges have little or no effect on the muzzle velocity and vertical shot dispersion on the target."

Now, this defies some basic logic for me. How could it be that you increase or decrease powder charge and the velocity remains almost constant. Why is that possible? Since pressure in the chamber/barrel is directly proportional to the powder charge and the pressure determines the muzzle velocity, the muzzle velocity must be directly proportional to powder charges too.
And if velocity is increasing with powder charges, there should be no point in the powder charge curve, where there's no vertical increase.

So, what's going on here? Why does the muzzle velocity and vertical dispersion on target become seemingly constant at whatever point we call a "node"?

This brings me another related question about "no two barrels are the same". If I have a say 62" long steel rod and two 30" barrels are cut out of it, chambered by the same reamer and put on the same action, they must be really close in how they behave. And I still hear a lot of talk about "barrel# 1 likes this load and barrel# 2 likes something completely different (sometimes a grain less of powder)". How could they be so different?

-Praveen

I will be the first to admit that my knowledge of internal ballistics is pretty lacking. I cannot tell anybody why 30.2 grns of 133 shoots .280 groups and 30.6 darn near cuts it in half.

like a lot of Short Range Benchrest shooters, I have done a lot of “load development” by nothing more than trial and error. You reach a point where things are looking good, then try small changes one at a time, changes that can often reap meaningful rewards.

But keep in mind, I do not shoot longer ranges. The furtherest I shoot is the 300 meter Tack Driver in November. So some of the items that are extremely important in Disciplines that involve longer ranges simply do not concern me.

in short, I tend to sacrifice all parameters of ballistic performance, both internal, external, and terminal in the quest to stack one bullet atop the other at 100/200 yards.

 

[JFrank]

Praveen noted; A node is where varying powder charges have little or no effect on the muzzle velocity and vertical shot dispersion on the target."

Although the WHY is beyond my comprehension, my 500 yard tuning ladders would seem to support the above statement.

 

[Mulligan]

I will be the first to admit that my knowledge of internal ballistics is pretty lacking. I cannot tell anybody why 30.2 grns of 133 shoots .280 groups and 30.6 darn near cuts it in half.

like a lot of Short Range Benchrest shooters, I have done a lot of “load development” by nothing more than trial and error. You reach a point where things are looking good, then try small changes one at a time, changes that can often reap meaningful rewards.

But keep in mind, I do not shoot longer ranges. The furtherest I shoot is the 300 meter Tack Driver in November. So some of the items that are extremely important in Disciplines that involve longer ranges simply do not concern me.

in short, I tend to sacrifice all parameters of ballistic performance, both internal, external, and terminal in the quest to stack one bullet atop the other at 100/200 yards.

I know this topic has been beaten to death and I've read through a lot of discussion and articles around "What is a node?". I read through the concepts of 'whip' or a longitudinal 'donut' like wave traveling down the barrel when a round is fired. All that is okay. However, what is not clear to me is the generally accepted definition of node (using a ladder or OCW method) that seems to be the following:
"A node is where varying powder charges have little or no effect on the muzzle velocity and vertical shot dispersion on the target."

Now, this defies some basic logic for me. How could it be that you increase or decrease powder charge and the velocity remains almost constant. Why is that possible? Since pressure in the chamber/barrel is directly proportional to the powder charge and the pressure determines the muzzle velocity, the muzzle velocity must be directly proportional to powder charges too.
And if velocity is increasing with powder charges, there should be no point in the powder charge curve, where there's no vertical increase.

So, what's going on here? Why does the muzzle velocity and vertical dispersion on target become seemingly constant at whatever point we call a "node"?

This brings me another related question about "no two barrels are the same". If I have a say 62" long steel rod and two 30" barrels are cut out of it, chambered by the same reamer and put on the same action, they must be really close in how they behave. And I still hear a lot of talk about "barrel# 1 likes this load and barrel# 2 likes something completely different (sometimes a grain less of powder)". How could they be so different?

-Praveen

I suspect there are lots of things in tuning that we cannot explain or explain very well anyway. Many of us that test a lot can recognize cause and effect, and this forum gives us a platform to share with others what we are seeing.

You will see long range Benchrest shooters “looking for overlap” that’s the flat spot. Several charges of increasing powder weights with increasing velocity all hitting at the same place vertically on the target.

Tony Boyer described this in his short range BR book, ….. look for three or four increasing powder charges where the point of impact does not change vertically.

CW

Edit
I have no idea why it quoted Jackie’s post.
My bad