Accuracy Nodes - Anyone experienced this with cast boolits?

[supersniper]

Has anyone experienced accuracy nodes with cast boolits?

My experience with long range precision rifles has shown that there are certain intervals of velocity which show the best accuracy. Most of the time the nodes are about 150 fps apart when working up loads.

Does this also happen with cast boolits?

[ShooterAZ]

Yes, it's no different than shooting jacketed. "Ladder test your loads to find the nodes".

[quilbilly]

I have a friend on this site (Rainier is his handle) who did the calculations on some of my best loads and confirmed that they are on the nodes.

[dtknowles]

I feel like nobody can calculate the velocity of nodes or predict the spacing of nodes. Just too many variables and not enough hard data.

Tim

[charlie b]

I guess someone could test the theory by running some Quickload data and then verifying.

Now days, when I use a new bullet or powder I do a long ladder. 20 loads, 0.1gn increase per round. After shooting plot the velocity to find the 'flatter' spots. That's where the nodes should be.

[Pirate69]

I played with this question about 6 months ago. I will see if I can pull my results together and share.

[Krag 1901]

Not sure what you'll mean by nodes. Is this a powder level that gives good accuracy and then as you increase the powder goes worse then gets better with a little more?
I have been experimenting with the quicker powders, 2400 to 4198 to RL10x range, for best accuracy and velocity 1700-2200 fps. My carbines don't seem to shoot as well with really slow powders I postulate because the barrels don't have the volume to get them up to pressure. Since the Krag and .308 have very similar case sizes they work very closely with these 20K -30K psi loads.
The thing I've noticed is that all the powders seem to work better when you push them a little. I went from 16 gr to 20 gr 2400 and 155/160 gr boolets in the .308 and Krag and got much better accuracy.
I have a new 314299 mold coming and look forward to using it as my Lee 309-200-R just doesn't work as well.

[Doughty]

You might find this interesting. I've played with it some. I've used it with QuickLoad to find a good starting place. It can save a lot of components.

http://www.the-long-family.com/OBT_paper.htm

[charlie b]

As the paper states. Nodes refer to the bullet leaving the muzzle at 'neutral' frequency points.

And, yes, some powders like to have more density than others. That's why some make poor reduced loads. Part of this is how a powder burn rate changes with pressure. If the pressure does not build fast enough the powder does not burn "well", resulting in higher extreme spreads in velocity.

[Larry Gibson]

I'm not convinced the "accuracy node" theory is valid. I've tested [worked up loads with target mostly at 200 or 300 yards] too many .223/5/56, .308W and 30-06 loads with match bullets under several different powders in many different rifles over the years which do not show any "accuracy node" preference. What is noticeable, as a chronograph was almost always used, is that once the powder begins to burn efficiently the accuracy levels off. That "leveling off" of accuracy can and most often does occur over several hundred fps at the top end. You won't see this with 3 or even 5 shot groups. Ten shot groups are needed. I never, with sufficient testing, found any such "accuracy nodes".

The use of a single 3 or even 5 shot group let alone single shots used in an "Audete Ladder" test really tell you nothing at worst and can be very misleading at best.

[onelight]

For me a ladder test is the first step in looking for a load and does not normally finish the project but gives me ideas on where to do more in depth testing .
But I am definitely a beginner on rifle testing even with 40 years experience . I like to shoot iron sighted hand guns so that is where most of my experience is.

[ShooterAZ]

I can remember Browning (and I think Winchester too) making the Boss system. A friend had one on a Browning A-Bolt, and I can remember him fiddling with it to find the proper settings. It is for adjusting the "vibration node" and was thought to help improve accuracy. I have no idea if they still make it or not, but apparently some gunmakers thought that there was at least some validity to it. Maybe it was just a fad, I really don't know.

https://www.browning.com/support/fre...tune-boss.html

[OS OK]

I think I'll follow this thread...I've been working with an 'F-class-BR' in .22lr & using a tuner...I swear, the more empirical evidence I pile up, the more it leaves me questioning everything I thought I knew about nodes.

One thing, it's not just the length & type of barrel and where the node is located in a particular load and it's characteristics but also the way we embrace the rifle, the hardness or softness of the surface the front rest and rear bag or bipod sits on, how much cheek pressure is applied...etc & etc. These other things add or take away from the 'supposed node' you think you have. These things act as a buffer and absorb or magnify the pressure waves cycling back and forth with in the rifle barrel & stock.
At least that has become the way I look at it from working with the tuner.
I may be out in left field with my assumptions but I feel there is definitely a lot we as shooters do, even doing our best sending the rounds for the best groups we can accomplish, we as humans can make a node look like something in-between nodes.

I don't think 5-shot groups as proof of a node are sufficient either...dtknowles showed me something in one of my threads that really opened my eyes.
He overlaid 4 ea. 5-shot groups that as individual groups looked pretty good, several almost one hole groups...but looking at 20 shots that group looked a whole lot different.

These were the individual 5-shot groups @ 50 yds....the first, within that 1" circle on the left is a warmer 5-shot group...he didn't include in his composite.



This is their composite, the 4 ea. 5-shot groups on the right...completely different looking.



It leaves me questioning whether or not I'm on a node or if I'm a lousy shooter or if there's more I can do to stiffen my bench or what?
This 'node seeking business' is as deep of a rabbit hole as it gets..."gotta love this stuff!"

[Larry Gibson]

For me a ladder test is the first step in looking for a load and does not normally finish the project but gives me ideas on where to do more in depth testing .
But I am definitely a beginner on rifle testing even with 40 years experience . I like to shoot iron sighted hand guns so that is where most of my experience is.

Keep in mind "incremental" load development [what many refer to as a "ladder" these days] is different than the "Audette Ladder" which is the "ladder" I was referring to.

[onelight]

Keep in mind "incremental" load development [what many refer to as a "ladder" these days] is different than the "Audette Ladder" which is the "ladder" I was referring to.

I didn't even know there was more than 1 kind to me it's just how I work up loads

[dtknowles]

I think I'll follow this thread...I've been working with an 'F-class-BR' in .22lr & using a tuner...I swear, the more empirical evidence I pile up, the more it leaves me questioning everything I thought I knew about nodes.

One thing, it's not just the length & type of barrel and where the node is located in a particular load and it's characteristics but also the way we embrace the rifle, the hardness or softness of the surface the front rest and rear bag or bipod sits on, how much cheek pressure is applied...etc & etc. These other things add or take away from the 'supposed node' you think you have. These things act as a buffer and absorb or magnify the pressure waves cycling back and forth with in the rifle barrel & stock.
At least that has become the way I look at it from working with the tuner.
I may be out in left field with my assumptions but I feel there is definitely a lot we as shooters do, even doing our best sending the rounds for the best groups we can accomplish, we as humans can make a node look like something in-between nodes.

I don't think 5-shot groups as proof of a node are sufficient either...dtknowles showed me something in one of my threads that really opened my eyes.
He overlaid 4 ea. 5-shot groups that as individual groups looked pretty good, several almost one hole groups...but looking at 20 shots that group looked a whole lot different.

These were the individual 5-shot groups @ 50 yds....the first, within that 1" circle on the left is a warmer 5-shot group...he didn't include in his composite.



This is their composite, the 4 ea. 5-shot groups on the right...completely different looking.



It leaves me questioning whether or not I'm on a node or if I'm a lousy shooter or if there's more I can do to stiffen my bench or what?
This 'node seeking business' is as deep of a rabbit hole as it gets..."gotta love this stuff!"

I usually break down accuracy into 4 pieces, the Gun, the Ammo, the Shooter and the Conditions. For a long time I wondered if the reason I was not shooting sub MOA groups was me, the Shooter. I bought a gun that was certain to shoot under .5 MOA, guess what I can shoot under .5 MOA groups. As handloaders we often focus on the Ammo, rightly so, I might add. Many of my guns shoot better with my Handloads than Factory that is until premium and match ammo became available in more calibers. Not many of us can afford to shoot a lot of premium or match ammo. The Shooter and the Conditions kind of interact, Conditions include more than the weather, wind, mirage etc. they include how you support the gun, rate of fire, lighting, target contrast, visibility of the POA. Some shooter deal with different conditions better than others and training and practice make a lot of difference as well as the quality of your vision.

Like OS OK's tuner, when you are shooting groups under 1 MOA. Different things start to matter, weight sorting bullets, barrel harmonics, stiffness of the bench, follow thru, friction of the front bag, grip pressure, shoulder pressure, cheek pressure (clean shave or stubble), velocity SD, even temperature and barometric pressure. How much do they matter, who really knows we just try to be consistent.

Tim

Tim

[M-Tecs]

I am with Larry. I am in the not convinced the "accuracy node" theory via the Audette Ladder test is valid. That being said barrel tuners are very valid for both centerfire and rimfire. The lot to lot accuracy variation of rimfire can lead a man to heavy drinking. Turners do help with that aspect.

[Pirate69]

I played with this question about 6 months ago. I will see if I can pull my results together and share.

There was a question raised on the use of Accuracy Nodes with cast boolits. I do not proclaim to be an expert in this area; but I will share what information I have been able to gather and my understanding of it.

This discussion on cast boolits is based on a fictional 180 grain 30-06 cast boolit load ranging from 1,4000 fps to 2,220 fps. Rounds are to be fired in a 22-inch barrel.
Accuracy Nodes seem to be based on the following theory:
The pressure pulse from the gasses in the chamber cause a traveling wave of stress that bounces back and forth along the barrel between receiver and muzzle, slightly changing the bore diameter in the process. Minimum dispersion of the shots will result when the rate of change of the bore diameter is at a minimum, and this dispersion will present the least sensitivity to load variations (charge, seating depth). It is the position of this wave and its effect on the muzzle at the point of bullet exit that is the cause of the majority of the dispersion around the mean POI.

Speed of the stress/pressure wave traveling up and down a barrel ranges is about 19,000 fps; depending on the material type of barrel being used. Cast boolits, are usually fired at a velocity less than 2,200 fps and can go down to subsonic speeds. The stress/pressure wave velocity will be constant; regardless of the exit velocity of the boolit. Therefore, the slower the exit velocity, the greater number of nodes or wave cycles. As an example, for 24-inch barrel, the number of nodes ranges from 19 nodes to 9 nodes for the exit velocity range of 1,400 fps to 2,200 fps. With this number of nodes, it seems that there may be a high probability of catching a node at any velocity as compared to a high velocity commercial round (4 nodes). I am not sure that there is an oblivious of benefit is trying to use accuracy nodes; you may already be there or may not be able to see a clear node with testing. High velocity loads seem to be a better application.

30-06 180 grain 24 inch barrel IMR 4064
FPS mS Nodes grains
1400 2.713 19 25.8
1500 2.547 18 27.8
1600 2.378 16 29.8
1700 2.212 15 31.8
1800 2.071 13 33.7
1900 1.938 12 35.7
2000 1.817 11 37.7
2100 1.709 10 39.7
2200 1.61 9 41.7
2900 1.088 4 Commercial


I have been able to compare a couple of previous OCW analyses to predicted Accuracy Nodes. The OCWs were shot at a range of 300 yards. I like to shoot OCWs at a distance far enough to see differences in groups. OCWs are shoot in a round robin fashion, with multiple rounds in each group. Each group is shot on a separate target and the group size measured against the POA.

The first OCW analysis is on a 300 Win Mag bull barrel on a milsurp Mauser action rifle. The selected load, from the OCW analysis, “sweet spot” was determined to be around 1.34 mS. The accuracy node for that barrel length and that velocity was determined to be 1.33 mS. This appears to be good agreement.

The second OCW analysis is on a 223 Rem Savage Axis rifle. The selected load, from the OCW analysis, “sweet spot” was determined to be around 1.09 mS. The accuracy nodes that bracket this exit time are 1.01 mS and 1.13 mS. This appears to be fairly good agreement with the 1.13 mS. An additional 0.1 grain of powder may have brought the load closer to a calculated node.

I will attempt to post the data and graphs for the two OCWs below. May have to get some help in doing so; we will see. Looks like the Accuracy Nodes have better application at the higher exit velocities than at lower velocities. Just food for thought.

In case someone wants information on varies nodes per barrel length. You will need to know the shot exit time at the muzzle for your load.

Optimum Barrel Time Chart below is in mSec (milli-second).

Barrel Length; inches 22 23 24 25 26
Node 1 7.50E-01 7.83E-01 8.16E-01 8.49E-01 8.82E-01
Node 2 8.23E-01 8.59E-01 8.95E-01 9.30E-01 9.66E-01
Node 3 9.39E-01 9.80E-01 1.02E+00 1.06E+00 1.11E+00
Node 4 1.01E+00 1.06E+00 1.10E+00 1.15E+00 1.19E+00
Node 5 1.13E+00 1.18E+00 1.23E+00 1.28E+00 1.33E+00
Node 6 1.20E+00 1.26E+00 1.31E+00 1.36E+00 1.41E+00
Node 7 1.32E+00 1.37E+00 1.43E+00 1.49E+00 1.55E+00
Node 8 1.39E+00 1.45E+00 1.52E+00 1.58E+00 1.64E+00
Node 9 1.50E+00 1.57E+00 1.64E+00 1.71E+00 1.78E+00
Node 10 1.58E+00 1.65E+00 1.72E+00 1.79E+00 1.86E+00
Node 11 1.69E+00 1.77E+00 1.85E+00 1.92E+00 2.00E+00
Node 12 1.77E+00 1.85E+00 1.93E+00 2.01E+00 2.09E+00
Node 13 1.88E+00 1.97E+00 2.05E+00 2.14E+00 2.22E+00
Node 14 1.96E+00 2.05E+00 2.14E+00 2.22E+00 2.31E+00
Node 15 2.07E+00 2.16E+00 2.26E+00 2.35E+00 2.45E+00
Node 16 2.15E+00 2.24E+00 2.34E+00 2.44E+00 2.54E+00
Node 17 2.26E+00 2.36E+00 2.46E+00 2.57E+00 2.67E+00
Node 18 2.34E+00 2.44E+00 2.55E+00 2.66E+00 2.76E+00
Node 19 2.45E+00 2.56E+00 2.67E+00 2.78E+00 2.90E+00
Node 20 2.53E+00 2.64E+00 2.76E+00 2.87E+00 2.99E+00
Node 21 2.62E+00 2.74E+00 2.86E+00 2.98E+00 3.10E+00
Node 22 2.71E+00 2.84E+00 2.96E+00 3.09E+00 3.21E+00

[Pirate69]

I see the files did not attach. I know how to attach photos using IMGUR. How do you attach files such as Word, pdf, Xcel?

[Pirate69]

I guess I can always take a picture of the data and graphs and insert it.

The first picture shows the OCW analysis for the 300 WM. The three rep round robin for ten loads are presented. The group center is then calculated as well as the 300 yard group size and MOA. For this test, the largest MOA was 1.4 and the smallest was 0.8; the ten group average was 1.0 MOA.

The group center is used to plot the results on a graph. The 300 WM graph is also shown in the first picture. The POI of all ten loads are plotted against a POA of 0,0. The "sweet spot" is usually indicated by a reversal of the curve and three shot group centers being close together. In this case, three groups were found to have POIs that were a maximum of only 0.4", both horizontally and vertically, from each other. Remember this is at 300 yards. This indicates that a powder charge of 68.0 to 68.6 grains IMR 4350 should have basically the same POI. The selected load from the test was 68.3 grains of IMR 4350. The selected load, using QuickLoad, “sweet spot” was determined to be around 1.323 mS. The accuracy node for that barrel length and that velocity was determined to be 1.33 mS. This appears to be good agreement.

https://i.imgur.com/uLZordY.jpg?1

The second picture shows the OCW analysis for the 223 Remington load. The three rep round robin for eight loads are presented. The group center is then calculated as well as the 300 yard group size and MOA. For this test, the largest MOA was 1.4 and the smallest was 0.5; the eight group average was 0.8 MOA.

The group center is used to plot the results on a graph. The 223 Rem graph is also shown in the second picture. The POI of all eight loads are plotted against a POA of 0,0. The "sweet spot" is usually indicated by a reversal of the curve and three shot group centers being close together. In this case, three groups were found to have POIs that were a maximum of 1.8 inches vertically and only 0.3 inches horizontally from each other. Remember this is at 300 yards. This indicates that a powder charge of 24.2 to 24.8 grains BL-C2 should have basically the same POI. The selected load from the test was 24.6 grains of BL-C2. The selected load, using QuickLoad, “sweet spot” was determined to be around 1.09 mS. The accuracy nodes that bracket this exit time are 1.01 mS and 1.13 mS. This appears to be fairly good agreement with the 1.13 mS. A decrease of 0.1 grain of powder may have brought the load closer to a calculated node.

https://i.imgur.com/mgIFIKv.jpg?1

Not sure if this is a guaranteed method to develop a load; but it should get you close to begin the process of refinement.