Discussion in 'Reloading Forum (All Calibers)' started by chop house, Jul 9, 2018.
curious as to the theory(ies) behind velocity nodes. (I am not speaking of accuracy nodes, btw.) thx
Velocity nodes are vibrations/oscillations in barrel movement, nothing more.
Not all barrels will show the same velocity node, although many that are similar lengths do.
It has to do with barrel time, as this is what governs barrel vibration movement.
Not sure the velocity node exists. My opinion - accuracy nodes are real and velocity is the easiest way we have to measure and communicate them to others. Not all chonos are equal, but labradar is closing the gap for many.
Flame away. I have tough skin.
They're not velocity nodes so much as optimal barrel times. When the rilfe fires, it whips around in a consistent but complex and hard to predict way. Timing the bullet's exit to coincide with a favorable point in that whipping motion (basically, an optimal muzzle direction and lateral velocity) is what much of load development is about. All of this depends on the rifle's components, the load, and the way the rifle is held, which is why you need to test for your own rifle. In practice, this means shooting groups while changing variables until they are small.
Node is also a misleading term, It's not a node in the way some people imagine it. Don't get wrapped around the term. Think "optimal timing of the bullet exit".
It's also only a part of the issue - there are other drivers to precision that have nothing to do with barrel time - the straightness of the bullet's entrance into the rifling, for example.
It's a made up term to confuse newer reloaders with meaningless terms...
I assume you mean a node identified using velocity instead the target to identify the "flat spot" via a ladder test. It amazes me that many feel they can shoot one shot per charge to accomplish this, completely ignoring the significant and unknown es and sd associated with each shot. For me there is no reason to believe this is a valid approach, even using 20 shots per charge, because I have never seen anyone present a correlation with target performance. Yes I've seen the videos where a single shot ladder shows a velocity flat spot, and then load this node to achieve great accuracy; but no target comparison to other loads. While I do not believe this is a valid approach vs using the target, I am open to accepting a valid comparison.
I have been reloading for 55 years, and I shoot a lot - I haven ever seen a "velocity node"
Opinion Of Al, TIFWIW.
the term "velocity node" is itself fairly recent.
IMO it's the result of a bunch of testing done 20yrs ago by some luminaries in the Bench Rest arena, notably Jim Borden, 'Doc' Jackson and Harold Vaughn altho others were involved. These guys were responsible for identifying and quantifying a process that came to be known as "sine wave tuning" which has morphed into "tuning" and now includes all sorts of half-assed partial explanations like "ladder testing" and "OCW" and "charge windows," "barrel time" predictors and even "predictive software" and loading charts and graphs reputed to "find and isolate tuning nodes"
Mostly without even knowing what a tuning node is.
Sine wave tuning is fascinating, counter-intuitive and magical AND WILL NEVER BE EXPERIENCED BY 99.99% OF ALL SHOOTERS! Because it's completely invisible until one gets down into the under-two-tenths group set.
But "velocity node tuning" offers a huge, wide open rabbit trail down which thousands of shooters per year hare.
In actual fact sine wave tuning is an interwoven combination of factors, the largest being charge weight, seating depth and neck tension. BUT..... early in the testing some folks like Jim Borden realized that given a tuned system, VELOCITY could almost be considered a constant, or at least used as a constant reference. An example of the usefulness of this fact can be found in Precision Shooting articles on the subject of preloading. Traditionally BR, real BR is a load-as-you-go proposition and "chasing the tune" is a fact of life but IF, and WHEN pre-loading is necessary it's possible to lock velocities into the center of a tuning window and chase tune without chasing clicks on the powder drop.
Now, powder lots vary. So whether pre-loading or not some folks live in fear of losing a tune, or a tuning regimen, when they run out of powder. And if you actually SHOOT yer guns, you WILL run out of powder. So Jim and others explored the idea of setting velocity right square in the center of a node and using it as the bedrock from which to tune loads. He talks (writes) of going to matches with PPC loads that varied as much as 1.5gr in charge weight but were NAILED DOWN per velocity.....
I could go ON and ON and ON as has been my wont regarding this "tuning" thing but I'll just say that In My Opinion snippets of this "velocity based" tuning leaked out into the general shooting consciousness and morphed into the term "velocity tuning."
And then into "velocity node" because rednecks like multisyllabic words and obscure high-sounding terminology. "Velocity node" in and of itself is garbage-speak, a complete non-descriptor. Hence the confusion, discerning people try to identify and isolate meaning and fail, not because "they can't understand it".... but because THEY CAN understand it. And it's not understandable
I say this because I've watched it happen.
On the innernet boards acros't thee world.
call it what you want but velocity node or flat spot or whatever your pet term is but to me it is just a powder charge that can vary .2 or more gns while the velocity remains relatively stable. I refer to them as flat spots in the velocity curve but if someone posts about a velocity node I understand what the poster is saying
Well now, here's something to ruminate upon.
Thank you for the information.
Many shooters have observed "flat spots" or "velocity nodes" while carrying out charge weight tests. It is not uncommon and will often be observed at pressures slightly below max pressure for a given cartridge, with case fill ratios in the 95-103% range. In fact, if you don't see the flat spot with a particular powder/primer combination, you can often visualize it simply by testing a few other primers.
I have often pondered what mechanism might account for this effect. Given the small sample size we typically use for velocity determinations during load development (5-10 shots), one could certainly make the argument that the flat spot is simply a fortuitous by-product of the small sample size. Unfortunately, that doesn't explain it away because for some people, the effect is quite reproducible. I have heard the explanation that the flat spot occurs when you have reached a point in the charge weight/velocity curve where combustion has become optimized. In other words, the charge weight, case volume, primer brisance, fill ratio, etc., are optimal relative to one another. Changing the charge weight slightly around that point does not substantially alter the burn rate/pressure curve. Once you go past the upper edge of the flat spot "charge window", you have reached a point where even though combustion and gas expansion is no longer at the optimal rate, the equilibrium has been shifted by the addition of excess propellant such that velocity will start to increase again. I have no idea whether this explanation correct, but it seems to account for at least some of the observations associated with the phenomena. Personally, I find the whole idea of a "flat spot" in the charge weight/velocity curve very counter-intuitive. Interesting...but counter-intuitive.
In the ladder test below. What ever you want to call that top 4 shot (thingy) with over 100 FPS and 2 gr of powder spread? It was good for 3 IBS 1000 yd records that following year. What ever it is called? let me know.
I would call it a "plana macula".
Why do so many of you long range record holders keep using those silly ladder tests to find those silly flat spots where velocity changes dont effect poi. (positive compensation) (sarcasm)
Mikegaiz, I would call that thingy a pressure ceiling.
That is a point of diminished returns with added powder. Diminished returns often manifests as diminished affects from variance. When a competitive 6PPC is running at ~75-80kpsi, it is so well into diminished returns that powder doesn't even need to be weighed any more. Tuning at that point is purely group shaping -for tightest.
Other cartridges can get there at lower pressures, depending on certain combinations.
Hey Alex..... I'm gonna' break my tradition of continually asserting that "no two similar barrels, no two similar bullets, no two similar rifles tune and shoot the same" because as of right now I'm fairly convinced that RL17 and H4350 show such similar burn characteristics that you can tune up a rifle with one, switch powders and match velocity and be back in the node.
(WHEwwww, I don't think I've ever put that idea'r into words before.... I might just regret it! LOL)
BTW if'n y'all would lay that frickin' ladder down and LISSEN to guys like Borden you'se might see that them "silly flat spots" actually map as a sine wave.......
This "Long Range guys VS Short Range" guys is what's silly.
Think Bart....there's a man can TUNE.....
Well, and he shoots OK too
It works for me. I would tell you why I do but then I would have to shoot you. I don't shoot people... just paper.
Lissen to yourself Alex......
Your statement is "flat spots where velocity changes don't effect (sic) poi"
There are 5 separate and discrete ideas floating around in this thread,
I don't think this pertains to the op's question in any way.....
Separate names with a comma.