Thread: Nodes = waste of time.

Here is a group shot today with a 223, a ladder test to see what sort of max it would tolerate with CFE223.



This is about how this rifle groups any day, its very reliable but not a real hummer.

So setting aside the first two shots tell me where the node is in this group . . . All I'll say is youre a better man than me if there is one. Ive shot quite a few ladders like this now, sometimes there will be vertical stringing as you'd expect as the velocity changes, but nodes, not so much.

Uh, not really sure what you’re trying to say? Number of rounds per charge weight? Number of times each charge weight repeated?

When you have the right pill and powder combination it just works, my dirty 06ai won't shoot 168g bergers or 165g nbts but it sure as shit loves 178gn ELDM's all using 2209 powder.
I think it was in one of the more recent hornady podcasts where they basically said if it doesn't shoot change powder or projectile or both.
Seems to be the case

Originally Posted by dannyb

When you have the right pill and powder combination it just works, my dirty 06ai won't shoot 168g bergers or 165g nbts but it sure as shit loves 178gn ELDM's all using 2209 powder.
I think it was in one of the more recent hornady podcasts where they basically said if it doesn't shoot change powder or projectile or both.
Seems to be the case

Only thing I'd add to Danny's comment is seating depth matters too from personal experience re my 284. Went from a 10 thou jump to 50 thou jump and she is humming

That type of test tells me the powder and projectile works for that rifle and is really only to find max preasure/velocity. Once you start seeing signs back off a wee bit and off you go

The only time I've really seen anything close to what you would expect to see from the tagline 'node testing' or 'ladder testing', is way out there where the small differences in velocity show something. Not a range I have easy access to at the moment... Also I think you have to be shooting in really calm stable conditions, off a solid rest and be on your game as anything else that introduces a variable that could conceal your results.

With the 300m range I have access to now, I've seen a couple of people try this and at the shorter distance while the results weren't as uniform as those above (which for a hunting group is pretty good) it still wasn't enough of a difference to show anything really useful.

I guess another option is you've managed to find one big node for that pill, powder and seating length combo...

With this approach in mind, does powder type even matter?

Does barrel length play a part in whether nodes are more pronounced or not??

I'll add does distance to target factor in? At 100 m many groups print the same, take it to 200 and the result can be very different. Admittedly I speak from experience with a long for weight projectile

Originally Posted by SPEARONZ

With this approach in mind, does powder type even matter?

Variations in powder burn characteristics between powders give you different pressure/time curves which gives you different cross velocity and angular rate. So yes.

Originally Posted by gimp

Variations in powder burn characteristics between powders give you different pressure/time curves which gives you different cross velocity and angular rate. So yes.

https://storage.googleapis.com/wzuku...nse%20Maps.pdf

Nodes exist in the angular rate and cross velocity but they don't co-incide and they only exist at one point in the distribution, e.g there may be a "node" i.e. a low point, in the angular rate at the mean, but the cross velocity may be at a higher value than elsewhere, and mean values represent the average across the population, there is actually a range of values higher and lower, and 1 standard deviation from the mean you will then have a much higher rate

Nodes sort of exist but you can't actually use them. Manipulation of powder charges doesn't Manipulate the angular rate and cross velocity predictably

I'll explain better when I'm on a computer not a phone cooking pukeko croquettes for dinner

Please do

Originally Posted by gimp

I'll explain better when I'm on a computer not a phone cooking pukeko croquettes for dinner

Hey that would be good. I don't know the basics of stats so everything needs explained, but it's proving highly useful each time I grasp a concept.

I wanted to get the 77s going a bit faster so after a bit of legwork on GRT I determined that I might make 2950 with them (at closer to 60,000 psi than the SAAMI limit of 55,000) so prepared fresh ladders using LVR and 2206H.

Here is the 2206H Ladder, shot in the S&L (the one above is another 223). The LVR ladder produced more velocity but it simply wasn't a "group", which highlights the instruction to change powders rather that shoot groups of each powder charge.



That's not a bad group for 5 with velocities from 2804 to 2947. For Christ's sake don't try and copy this load without a careful work up.

Your rifle does not shoot every bullet into one hole. It has a "cone of fire" where bullet impacts are dispersed around the mean point of impact. It shoots groups. What causes this dispersion?


A series of factors, but the primary sources of random error at short range are the angular rate and the cross velocity. The magnitude of other factors is generally insignificant at close ranges. You can read this for more detail if you want. https://dsiac.dtic.mil/articles/rand...er-dispersion/

The angular rate is wobble around the CG of the bullet caused by things like principle axis tilt, where the bullet is slighlty asymmetrically engraved in the rifling, etc. Gas flow effects at the muzzle can also induce angular rate. The cross-velocity is a velocity vector, with a magnitude and direction transverse to the bore/line of sight - your bullet has a bit of velocity sideways/up/down when it exits the bore, due to CG offset, "barrel whip", etc. The magnitude and direction of both of these is variable shot to shot, depending on the shape of the pressure-time curve - even with extremely consistent loads there are small variations in how pressure builds over time in the bore. Because the pressure/time curve is variable, the angular rate and cross velocity are also variable (in size and direction).


You can model (you could conceivably measure) the angular rate and cross velocity, fitted to real-world data. You might find a load where, at the mean pressure/time function, the angular rate is low - a "node" for the angular rate. The cross-velocity however may still be high. They are not correlated so finding a low point for one value does not mean the other will be low.

In addition, your pressure-time function is ALSO variable. So while you may have a low angular rate at the mean pressure/time value, you will have different (higher) angular rate values for shots that have pressure/time characteristics that aren't right on the mean. Any particular load will have a range of angular rate and cross velocity values. You cannot tune it by varying powder charge to pick a low value. You have to shoot a very large sample size to even know what you have. Because different powders produce very different pressure/time curves, the same bullet at the same speed but with different powders can have quite different dispersion characteristics; 1 may be much more variable in the angular rate/cross velocity, or have much larger values.

The article I linked from Jeff Seiwert shows all of this. It is quite difficult to understand. It is most practical to not dig too deep into the theoretical stuff, and just try to measure your precision meaningfully, and determine whether it meets your requirements, and if it does not, pick a different bullet or powder. Most efforts to demonstrate anything else are just noise in poor approaches to measurement.

https://storage.googleapis.com/wzuku...nse%20Maps.pdf