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.

Attachment 269816

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 :cool:

Quote:

---

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 :cool:

---

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

Quote:

---

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.

Quote:

---

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

Quote:

---

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.

Attachment 269870

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

Thanks. I think people (me in particular) have been confusing the issues around barrel harmonics (barrel whip, oscillations etc) with nodes, thinking they "cancel out" at some certain velocities. The S&L has a very slim barrel, and powder choice (and the corresponding effects that has) as much as anything predicates how it will shoot.

A thin barrel of very high quality will have less "barrel whip" (hence induce less cross velocity) than a poor-quality thick barrel

Here is the ladder shot today with the LVR, just no comparison or group but worth including to give a full picture. It has one more round cause I don't really trust some of the ball type powders, hence starting a bit lower (relative to the 2206H)

Attachment 269873

Whats that 26/26.3 grn velocity about? 300 fps jump for .3grn

I'd guess transcription error. 2963.

Quote:

---

Originally Posted by gimp

I'd guess transcription error. 2963.

---

Oops - yup. 2963

You are not including the other very important factor in equation.the one that can have,and often does have the most impact on impact destination ( see what I did there lol) the nut behind the butt will change things by huge amount or you either having a bad day of just not in the zone. I know personally if my back is sore I can't shoot for shit.a mild headache or tired eyes do the same. A wise man once said to call it honestly. If you think your wobbling around 2" you sure as shit won't group tighter than that.

Quote:

---

Originally Posted by Micky Duck

You are not including the other very important factor in equation.the one that can have,and often does have the most impact on impact destination ( see what I did there lol) the nut behind the butt will change things by huge amount or you either having a bad day of just not in the zone. I know personally if my back is sore I can't shoot for shit.a mild headache or tired eyes do the same. A wise man once said to call it honestly. If you think your wobbling around 2" you sure as shit won't group tighter than that.

---

Quite right MD, that with enviromental considerations . . . I always make a call on how good my "hold" is for that day, in good morning light when my eyes are at their best I reckon I can hold to about 0.5 MOA but as the day goes on so does my concentration and eyesight and my hold can easily balloon out to over 3/4 MOA, and being a bit tired or grumpy and some wind, then a 1.00 MOA hold is as good as I can do.

If I'm shooting someone else's rifle I always take something of mine I know is going well as a "control", both for myself and them too sometimes.

Quote:

---

Originally Posted by gimp

A thin barrel of very high quality will have less "barrel whip" (hence induce less cross velocity) than a poor-quality thick barrel

---

Been thinking this through at idle moments - all things being equal I'm not sure barrel 'quality' will have that much effect on how the tube performs for 'whip' or resonance.

Quality of the barrel work will have a huge effect on how the barrel performs for accuracy, cleaning and velocity sure, but as far as I can work out the type of steel used for barrel construction is fairly equivalent (cro-moly vs 416 stainless - maybe one or two options with other construction methods like carbon wrap but for the purposes of this I'm happy to ignore those). So all things being equal, and both options being the same caliber and length the barrel with the most mass will be stiffer and have less whip (thicker walled). Two barrels of the same mass but different lengths, the shorter will have less whip (thicker wall section on the tube). Two barrels of the same mass but different lengths (longer one fluted) the shorter barrel will be stiffer but if they have the same length and mass but one is fluted the thicker wall section should be slightly stiffer (but not as stiff as if it wasn't fluted).

More mass = stiffer + less whip and I'm not sure that there is any way around that. The quality issue comes in to the repeatability of the barrel where things like how concentric the bore is (did the driller get it in the middle of the stock), smoothness of the rifling, general quality and accuracy of the machining work and also how good was the heat treatment/stress relieving was. That's a major which effects how evenly the barrel shifts as it heats up and again all things being equal the heavier barrel heats up slower so shows less variation here. But that still doesn't affect 'whip' as such.

The slimmer tube might heat up quicker and show more effect with temperature, and will have more barrel whip than a more cheaply machined but thicker walled barrel. But I'd say it is a fair assessment that barrel whip is only one factor that affects performance and repeatability - trying to shoot some rifles in freezing temperatures shows a huge difference in POI and 'zero' as the bedding tensions have changed. A rifle that shows this sort of variation is a good candidate for bedding work...

Barrel whip is largely a function of straightness and concentricity of the bore. Bore diameter consistency also affects principle axis tilt of the projectile.


Regardless, if we zoom up one level - it's sort of immaterial. If you want good results consistently, you want to get a very high quality barrel. It is observable that good cut rifled match barrels of thin contours provide the sort of precision that loses benchrest matches. It's in the same ballpark. I'm getting benchrest-match-losing 5rd group sizes with factory match ammo from a sporter weight barrel. Whatever characteristics are providing that precision is sort of irrelevant. Consideration of the game you want to get involved is probably wise, if you really want to compete in benchrest you may as well use up every gram of the weight allowance and get a fat tube.


Quality barrels simply do not move measurably with temperature, inside the kind of use cases that are actually practical. Yeah if you sat and continuously fired it for 200 rounds the precision may degrade. Precision degrading in 3 rounds due to "barrel heat" is a joke. 10-20 rounds with most cartridges doesn't seem to be a problem. If your group "opens up with heat" it's one of 2 things - your barrel is defective, or you are not measuring your precision properly in the first place and misinterpreting that.

Bedding problems are a defective rifle. Don't get or keep a defective rifle.

No expert but 23.3-23.6 seems to be the smallest gap in velocity. I would have done that ladder 3x to see if it was repeated. Then go middle of road and do a seating depth test for groups