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Node Theory

I have read and listened to a lot regarding tuning your loads using the Node method and wave theory. I'm not disputing any of these ideas and they do seem to be the most prevalent among long range competitors. However, I have a question that perhaps some of the engineers on here might be able to better explain. All of these node and wave methods, are based on pressure curves and bullet time inside the barrel. That part makes easy to understand sense to me. However, even with powders such as Varget, which are supposed to be temperature stable, there is about a 30-40 fps difference in muzzle velocity from a 45F day to a 85F day. That tells me that the bullet time in barrel and the pressure curve has also changed a great deal as those ambient temperatures change. Its also the case that during a string, our barrels get very hot and the shots tend to move more vertical as the barrel heats up, so again the pressures and bullet time in the barrel is changing. But I don't know of anyone that has several different loads developed using the nodes method, for temperature changes of say 10F increments. I have not found a significant difference in accuracy as a result of these temperature changes, using the same load, although there is certainly a difference in vertical sight adjustment at longer ranges. Can someone explain how the node and/or wave method can be valid when taking into consideration these ambient changes that don't seem to affect the accuracy of the developed load?
 
You don't need to ponder theory, empirical results work just fine. From your starting load, increment three-shot groups by .5 grain until practical maximum is determined. Some point below maximum will usually show good grouping and low ES. Those two do not always coincide. Test seating depth in three-shot groups and .003" increments until best accuracy is located. If low ES and best accuracy do not coincide, that is where a tuner can benefit. The tuner can be adjusted to align accuracy and low ES. At that point, you are ready to go and no theory was involved in the process. [br]
A reasonably stable powder and wide charge window will ensure that the load works well in a variety of conditions. If the temperature has changed significantly, I take remaining rounds from a match and run them over my chronograph for group to see if the load still performs. If it is off, I'll adjust it up or down in a short series find the sweet spot. This is usually not necessary unless there is a large temperature change.
 
Donovan, I don't know if you subscribe to the OBT theory, but have you ever done any correlation to see if the nodes you have found (like the one in your post) match up with an OBT-predicted node? Clearly you have a nice, wide node there, but I'd be interested to know if OBT predicted that node or not.
 
merc99 said:
Can someone explain how the node and/or wave method can be valid when taking into consideration these ambient changes that don't seem to affect the accuracy of the developed load?

I think the point of your question may have been missed here. IMO, it's an excellent question and I'm looking forward to seeing the explanation.

If, node theory is based exclusively on pressure curves and bullet time inside the barrel;
Then, any change in pressure and/or barrel length travel time should move the node.

If you haven't read this, you should:
http://www.the-long-family.com/OBT_paper.htm
 
Donovan,
Now that you have found your node, what do you do next? I sometimes shoot ladders, and they work for me. They at least get me in the ball park. Do you shoot groups in that window to find the best charge? Do you work seating depths after you determine your powder charge?
Alex
 
I have used both Audette ladder test and OBT to find accurate loads. The nice thing about the Audette ladders is they show how wide the node are and if your barrel has residual stresses. I never could get a good Audette ladder on a factory barrel with one shot so I increased it to three. I could then see the groups open and close and also see them orbit an ellipse from the stresses left in.

With OBT I do use Quickload to predict nodes but I back it up with shortened ladder tests over a chronograph and I also have the Pressure Trace. This is usually two loads at .2 grain increments above and below the predicted load. If the ladder tests show the load getting smaller in one direction or the other I go center on the outer load in that direction and test again. Chronograph average speeds verify the loads predicted. The pressure trace is used sparingly because I find it a PIA to setup. I have one of the originals and the newer units look a lot easier.

Shooting strings will open up a group if you let the barrel heat up. The thinner the barrel the easier it is to overheat it. It is real easy to test and just about everyone here that has shot groups has repeated it and got the same results.

Changes in temperature affect barrel harmonics. I know at higher temperatures heating metal up makes it more elastic but a metallurgist would have to speak on heating a barrel to 150 degrees and what effects that has. If I remember right higher temperature lower the density therefore lower the speed of sound in the metal. Is it enough to matter? OBT only accounts for one, maybe two modes, of barrel vibration that are affected by speed of sound. See Varmint Al's site for that: http://www.varmintal.com/amode.htm Finding the wide node is probably when all those modes except #5 are in alignment near the apexes of the sinusoidal wave (1,2,3,7) and when the muzzle diameter is at a minimum (4,8). Mode 6 I'm not sure matters but my guess is that when the barrel is shortest is when the amplitude for nodes 1,2,3 and 7 is lowest and the node is bigger. Do some of the factors cancel out so the node theory works. It's a good question. I would love to have a private range with all the instrumentation I need to find out.

After that there are the effects of increased temperature on the powder and primer.

Look here for some interesting reading: http://www.shootingsoftware.com/tech.htm


Have you read Rifle Accuracy Facts by Harold Vaughn?
 
I'm with Steve on this: Empirical data outweighs any theory.

That said, I subscribe to the OBT theory to determine where to look for a node rather than to tell me what the optimal load is.
 
I but be living in the past. I do it all at 100 yds. I run up and down on the powder charges till it gets the smallest,then in and out on the seating depth till it gets the smallest. Then i go back to the powder and move at smaller .1 increments and then go to 5 shot groups with what i think is the best. Then back it up with different barrels and guns. I then go to find the quality of the barrel. Next test is the first match….. jim
 
I just want to thank all the posters for their replies. It does seem that a balance between the theories and empirical findings is what ends up working the best. I do most of my load testing at 200 yards, and also over a chrono. It seems that when I find that a load is grouping very well, and over the chrono the speed is not increasing much as the charge increases, that seems to be the sweet spot. I guess that would relate to a ladder test. Then I tinker with seating depth and fine tuning.
 
johara1 said:
I but be living in the past. I do it all at 100 yds. I run up and down on the powder charges till it gets the smallest,then in and out on the seating depth till it gets the smallest. Then i go back to the powder and move at smaller .1 increments and then go to 5 shot groups with what i think is the best. Then back it up with different barrels and guns. I then go to find the quality of the barrel. Next test is the first match….. jim

I do the same, but at 200. I usually find my self doing a ladder though on a hunting rifle or a new catridge I have no experiance with.

The thing I find odd is seating depth. I have never, ever owned a rifle that shot best in the lands. I always try to get them to shoot in the lands, but they always end up jumping a bit. It seems like the better shooters shoot in the lands more often then not.
 
The reason i've always used 100 yds, i can control the conditions better with wind flags. The best reason is it's in my back yard and it's load and shoot. It's called a cone of dispersion and it doesn't get any smaller,so tuning at 100 yds. will carry through to 1000 yds. After i develop a load i will zero dead on at 100 and set my scope elevation and windage to zero. Come up 10 min. for 600 or 24 min. for 1000…… jim
 
johara1 said:
... It's called a cone of dispersion and it doesn't get any smaller, so tuning at 100 yds. will carry through to 1000 yds. ...
In theory that idea has some merit; as a practical reality it doesn't work precisely like that.
You can produce a .25 inch group at 100 yards with a variety of loads but when their velocity begins to decay their trajectory can be expected to be dramatically different.
 
Thoughts to ponder when tuning at the range.
Unless you are in a tunnel range or always call the wind perfectly, the group width has less value than the group vertical. Many good loads have been overlooked due to wind drift affecting a test group. That 1" vertical and 5" horizontal 5 shot test group at 1000 might have been the load for a record, ya think...
Greg
 
Blaster-37 said:
Thoughts to ponder when tuning at the range.
Unless you are in a tunnel range or always call the wind perfectly, the group width has less value than the group vertical. Many good loads have been overlooked due to wind drift affecting a test group. That 1" vertical and 5" horizontal 5 shot test group at 1000 might have been the load for a record, ya think...
Greg

Up to a point apparently. Tony Boyer talks about barrel harmonics in more than the vertical plane and says he often picks groups that are slight more vertical but "rounder." I am pretty sure I saw an example of this one day when I was shooting a scope tracking test with two of my rifles on a dead calm morning at 100 yards. I thought both were tuned the same but one of them had all of the vertical in the horizontal plane while the other was all in the vertical plane. I almost never lucky enough to do any serious testing under those conditions so maybe it was just a one-time thing but it got my attention.
 
dmoran said:
Lapua40X,

For the most part I agree with you. But there are exceptions, and those being experience.

Donovan

The only element that was left out of the earlier statement was a qualifier that addresses the reality of how MV is going to affect the trajectory beyond 100 yards. I can shoot a fairly tight group at 100 yards with a .22LR under perfect conditions, but that doesn't mean I can expect the group of 1 inch at 100 yards to hold together for a consistently accurate group at 1000 yards. The "cone" model only works if the bullet can reach the target with reliable velocity.
My motives for insisting on being clear with comments that relate to long range shooting is so that newer shooters don't become confused when they read our advice/comments relating to accuracy over long distances.
As experienced shooters, you and I understand what was meant. A new shooter might not. ;)
 
I think some here are missing the point,in load development i have better control of the conditions i shoot in. There are no exceptions,The guns i use shoot small at 100 display the same small groups at 1000 but the effects of conditions on the way open them up to 2"+ groups. You can not tune a load at longer ranges when you have so many variables. I mile per hour change at 1000 is huge so how can you tune in something you can't see? I feel you get a more reliable load tune up close under a more controlled conditions.
I speak of a cone of dispersion,this was hammered in my head in the Marine corps, What a shooter can hold and a rifle can hold and what ammunition can hold. Sorry if you never heard of it
I did slow my loads down and for some reason they shoot better in the wind, amazing right…… ;)….jim
 
johara1 said:
I think some here are missing the point,in load development i have better control of the conditions i shoot in. There are no exceptions,The guns i use shoot small at 100 display the same small groups at 1000 but the effects of conditions on the way open them up to 2"+ groups. You can not tune a load at longer ranges when you have so many variables. I mile per hour change at 1000 is huge so how can you tune in something you can't see? I feel you get a more reliable load tune up close under a more controlled conditions.
I speak of a cone of dispersion,this was hammered in my head in the Marine corps, What a shooter can hold and a rifle can hold and what ammunition can hold. Sorry if you never heard of it
I did slow my loads down and for some reason they shoot better in the wind, amazing right…… ;)….jim

Jim,
Have you tuned any big guns at 100 for 1k competition? I am wondering if the same holds true for the big stuff like a 300 or 338? You always hear about the big bullets not going to sleep....
 
johara1 said:
The reason i've always used 100 yds, i can control the conditions better with wind flags. The best reason is it's in my back yard and it's load and shoot. It's called a cone of dispersion and it doesn't get any smaller,so tuning at 100 yds. will carry through to 1000 yds. After i develop a load i will zero dead on at 100 and set my scope elevation and windage to zero. Come up 10 min. for 600 or 24 min. for 1000…… jim

I agree with you 100%. I don't want a load development session to also be wind reading 101.

I wait till after dark when the conditions are zero....midnight...2am..whenever, and I do it at long range. My current setup is at 750 yards.
 
I really don't mess with big ones anymore, i'm 70 and i don't have but one eye left. Besides i watch them get blowed off the paper at White horse at the national two years ago and the little gun hung in there…… jim
 
4xforfun said:
... I wait till after dark when the conditions are zero....midnight...2am..whenever, and I do it at long range...

For what its worth, I think this is a mistake. I want to know what my load is doing in the conditions I will be shooting in. It is certainly possible for a load to look great in a "zero" condition, but be overly wind sensitive in a stronger wind.

The only time I want to shoot in a still condition is to verify a problem with my equipment - ie I just cant get some piece of the system to work no matter what, and I want to test it with as few variables as possible.
 

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