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Ladder test with only a Chronograph
- Thread starter BJung
- Start date
This is a general reloading topic, so I will move it out of the casting sub-forum for you.
There are velocity nodes. They've been known about for decades; pretty much ever since consumer chronographs went on the market. They may correspond to the sweet spots predicted by Chris Long's Optimum Barrel Time theory. The limitation is they occur more frequently in a series of load increments than the vertical POI flat spots identified by an Audette Ladder do, and while the gun will usually shoot better at one of these velocity flat spots, unless you get both the velocity and the barrel vibration flat spot to coincide, the consistent cloverleaf may elude you. Tuning bullet seating depth is another factor that tends to bring loads in, though it may be doing that by affecting the exact phase of the pressure wave at muzzle exit that Long talks about. So there are two and possibly three tunable factors you need to coordinate for highest accuracy.
You can prove the above to yourself if you have a gun with a barrel tuner, like the Browning B.O.S.S. Use the chronograph to find your velocity flat spots and load to one of them and then dial in the tuner and you will see the groups get even smaller. The tuner controls where an Audette ladder POI flat spot turns out to be.
There are velocity nodes. They've been known about for decades; pretty much ever since consumer chronographs went on the market. They may correspond to the sweet spots predicted by Chris Long's Optimum Barrel Time theory. The limitation is they occur more frequently in a series of load increments than the vertical POI flat spots identified by an Audette Ladder do, and while the gun will usually shoot better at one of these velocity flat spots, unless you get both the velocity and the barrel vibration flat spot to coincide, the consistent cloverleaf may elude you. Tuning bullet seating depth is another factor that tends to bring loads in, though it may be doing that by affecting the exact phase of the pressure wave at muzzle exit that Long talks about. So there are two and possibly three tunable factors you need to coordinate for highest accuracy.
You can prove the above to yourself if you have a gun with a barrel tuner, like the Browning B.O.S.S. Use the chronograph to find your velocity flat spots and load to one of them and then dial in the tuner and you will see the groups get even smaller. The tuner controls where an Audette ladder POI flat spot turns out to be.
kilotanker22
New member
I have done this a few times. I will do the Velocity ladder test. Then pick the flat spot and load right in the middle. I do this for each flat spot in velocity I find across the range of powder weights.
I then see which load shoots better, then I adjust or play with bullet seating depth to finish bringing it in. I have done this with several rifles and thus far it has worked. I will note that every single one of my "best loads" have had very very low ES and SD numbers. I don't think that's a coincidence.
I then see which load shoots better, then I adjust or play with bullet seating depth to finish bringing it in. I have done this with several rifles and thus far it has worked. I will note that every single one of my "best loads" have had very very low ES and SD numbers. I don't think that's a coincidence.
It's an interesting idea, but I think to get a realistic idea of where the velocity flat spots are, you'd have to fire several shots (the more the merrier) at each load. Reason being, even with single-digit standard deviations for the individual loads, it would be hard to find the sweet spots with only one or two shots. YMMV
Tim
Tim
As Unclenick and Kilotanker point out a low ES/SD does not guarantee a accurate load but every good load I have found for long distance seems to have low numbers
here is a thread by Erik Cortina of Team Lapua Brux Borden on using the chrono Long range load development at 100 yards.. There are over 100 pages in that thread now.
I use the same method except I do the bullet jump test before doing the powder charge test. I swear by it, even though a lot of "experts" here told me it would not work.
here is a thread by Erik Cortina of Team Lapua Brux Borden on using the chrono Long range load development at 100 yards.. There are over 100 pages in that thread now.
I use the same method except I do the bullet jump test before doing the powder charge test. I swear by it, even though a lot of "experts" here told me it would not work.
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What you are seeing is that any node that tends to improve consistency will tend to improve accuracy if all else is equal. There are just more than one kinds of node, and the trick is to get them all to play together for maximum effect. So, for example, you could have a pretty jagged Audette or OCW ladder that doesn't have the tightest groups but that is clearly identifying where muzzle deflection is optimal and then go on to tighten groups up by finding a bullet and powder and seating depth combination that also has a velocity flat spot coincident with that phase of the muzzle deflection. Things that improve consistency, be it in velocity or muzzle position, can stack up.
TimRB,
You are correct. Typical Audette and OCW ladders run over 20 shots, and if you want to see where your velocity flat spots lie, it takes the same sort of effort. I know there are guys on YouTube running just 10 shots, but that's because you can usually get at least one velocity flat spot identified in that number if you shoot carefully. But they then settle on that flat spot's load without knowing that if they'd have expanded the range they might have found one in a muzzle whip flat spot that further shrank the group considerably.
Then there are rounds that need to be fired to determine optimal seating depth. I've seen a YouTube video of a fellow starting 15 or 20 thousandths off the lands and changing seating depth in very small increments of a few thousandths, getting closer and closer to the lands. He shot, IIRC, five-shot groups at each seating depth, all of them pretty good, and then identified one a bit smaller than the others as best. The problem is, with five-shot groups he could have fired them all at the same seating depth and random probability says he would still have got one group as small as the one for which he concluded he'd found the best seating depth. It's easy to delude oneself in these matters. The real problem is he didn't try nearly a wide enough range of seating depths to know he was at the best point. Berger has found seating depths as much as 0.150" off the lands will shoot best with some bullets in some rifles. So you really want to move bullets in increments of at least 0.020" to fine the most promising region, and then refine down to smaller steps around that spot.
In the mid '90s, the late Dan Hackett described loading 0.020" off the lands as a matter of course because there was a general concensus at the time that this was optimal. He had a 220 Swift that would not average tighter than 0.5" 100-yard 5-shot groups no matter how he tuned the powder charge. Then one day, when switching between bullets, he inadvertently turned the micrometer head on his seating die the wrong way to compensate for a longer ogive, and wound up loading 20 rounds 0.050" off the lands before he discovered the error. He considered pulling and reseating them, but decided just to shoot them up in practice. To his amazement the 5-shot groups from the bullets seated that far back gave him two 0.25" groups and two true bugholes in the 1's (below 0..2").
So, there's a good deal to do in tuning. I may have 100 rounds down range before I'm really sure I've ferreted out all I can by testing.
TimRB,
You are correct. Typical Audette and OCW ladders run over 20 shots, and if you want to see where your velocity flat spots lie, it takes the same sort of effort. I know there are guys on YouTube running just 10 shots, but that's because you can usually get at least one velocity flat spot identified in that number if you shoot carefully. But they then settle on that flat spot's load without knowing that if they'd have expanded the range they might have found one in a muzzle whip flat spot that further shrank the group considerably.
Then there are rounds that need to be fired to determine optimal seating depth. I've seen a YouTube video of a fellow starting 15 or 20 thousandths off the lands and changing seating depth in very small increments of a few thousandths, getting closer and closer to the lands. He shot, IIRC, five-shot groups at each seating depth, all of them pretty good, and then identified one a bit smaller than the others as best. The problem is, with five-shot groups he could have fired them all at the same seating depth and random probability says he would still have got one group as small as the one for which he concluded he'd found the best seating depth. It's easy to delude oneself in these matters. The real problem is he didn't try nearly a wide enough range of seating depths to know he was at the best point. Berger has found seating depths as much as 0.150" off the lands will shoot best with some bullets in some rifles. So you really want to move bullets in increments of at least 0.020" to fine the most promising region, and then refine down to smaller steps around that spot.
In the mid '90s, the late Dan Hackett described loading 0.020" off the lands as a matter of course because there was a general concensus at the time that this was optimal. He had a 220 Swift that would not average tighter than 0.5" 100-yard 5-shot groups no matter how he tuned the powder charge. Then one day, when switching between bullets, he inadvertently turned the micrometer head on his seating die the wrong way to compensate for a longer ogive, and wound up loading 20 rounds 0.050" off the lands before he discovered the error. He considered pulling and reseating them, but decided just to shoot them up in practice. To his amazement the 5-shot groups from the bullets seated that far back gave him two 0.25" groups and two true bugholes in the 1's (below 0..2").
So, there's a good deal to do in tuning. I may have 100 rounds down range before I'm really sure I've ferreted out all I can by testing.
kilotanker22
New member
I learned the lesson Unclenick refers to about seating depth this past year with a 300 win mag. I couldn't get that thing to shoot for the life of me. Even after having really good flat spots in velocity. Now when I say it didn;t sshoot. I mean at best 1.5" groups at 100 yards. Someone on this forum advised that I seat my bullets deeper into the case. So I set up a test from .020 off the lands all the way up to .145 off the lands. To make a long story short. That particular load really dialed in when seated more than .01 away from the lands.
Since I have begun to test seating depth across a much larger range than before.
Since I have begun to test seating depth across a much larger range than before.
I find it interesting that the OBT paper claims that the barrel's resonant frequency range is about 10 times higher than what's been measured and calculated by vibration analysis engineering disciplines.
And my Garand barrels with .001" bore and groove enlargement at the muzzle from cleaning rod wear are no less accurate than when new. They still tested sub 2/3 MOA at 600 yards
And my Garand barrels with .001" bore and groove enlargement at the muzzle from cleaning rod wear are no less accurate than when new. They still tested sub 2/3 MOA at 600 yards
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Bart,
The resonance you are referring to are transverse. Much slower than the pressure waves (P-waves) Long is referring to that travel at the speed of sound in the barrel. I can see them overlayed on pressure plots I've taken with the pressure trace instrument. While I don't subscribe to the idea they are solely responsible for tuning, getting them synchronized with the harmonics you are talking about seems to be part of what makes a barrel a "hummer".
The resonance you are referring to are transverse. Much slower than the pressure waves (P-waves) Long is referring to that travel at the speed of sound in the barrel. I can see them overlayed on pressure plots I've taken with the pressure trace instrument. While I don't subscribe to the idea they are solely responsible for tuning, getting them synchronized with the harmonics you are talking about seems to be part of what makes a barrel a "hummer".
Nick, I was referring to the angular beam bending vibration lowest frequency of the barrel as its resonant one mentioned in the OBT paper. Not the 3rd or 4th harmonic higher ones that effect positive compensation for muzzle velocity nor the shock waves moving from breech to muzzle, the transverse or p-waves you mention.
What's the speed of sound in barrel steels?
What's the speed of sound in barrel steels?
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Has anyone done a ladder test by just recording the MV?
Try googling "Saterlee Load Development".
T. O'Heir,
If any of what you said were true, ladders wouldn't work and barrel tuners wouldn't work. But ladders do work, and barrel tuners work.
Bart,
Varmint Al has good animations showing 8 modes of barrel resonance from 82 Hz to 4171 Hz that depend on barrel length and mass and moments of inertia. The P-wave's resonant frequency is a 9th mode that depends only on the speed of sound in the barrel and not on its mass or moments of inertia. It's like a compressed lump that runs up and down the barrel. A traverse analog would be the lump in a long, taught rope that runs to a tied end and back to your hand when you crack it up and down abruptly. One full cycle of a p-wave resonance is how long it takes to traverse the length of the barrel twice; down and back. It's at close to the frequency of that 8th mode, but doesn't have a null in the center like the 8th mode does.
The speed of sound in a barrel depends on the kind of steel, but Long uses 18,916 ft/s down its length. That is for stainless barrel steel. The Engineering toolbox puts more general stainless steels at 18,991 fps and 1% carbon steel at 19,483 fps, or about 3% higher than barrel stainless. I found a reference with 0.2319 in/uS for mild and carbon steel alike, which would be 19,325 ft/s. So you can get a sense of the range from this.
If any of what you said were true, ladders wouldn't work and barrel tuners wouldn't work. But ladders do work, and barrel tuners work.
Bart,
Varmint Al has good animations showing 8 modes of barrel resonance from 82 Hz to 4171 Hz that depend on barrel length and mass and moments of inertia. The P-wave's resonant frequency is a 9th mode that depends only on the speed of sound in the barrel and not on its mass or moments of inertia. It's like a compressed lump that runs up and down the barrel. A traverse analog would be the lump in a long, taught rope that runs to a tied end and back to your hand when you crack it up and down abruptly. One full cycle of a p-wave resonance is how long it takes to traverse the length of the barrel twice; down and back. It's at close to the frequency of that 8th mode, but doesn't have a null in the center like the 8th mode does.
The speed of sound in a barrel depends on the kind of steel, but Long uses 18,916 ft/s down its length. That is for stainless barrel steel. The Engineering toolbox puts more general stainless steels at 18,991 fps and 1% carbon steel at 19,483 fps, or about 3% higher than barrel stainless. I found a reference with 0.2319 in/uS for mild and carbon steel alike, which would be 19,325 ft/s. So you can get a sense of the range from this.
Nick, I've always used the barrel's lowest vibration frequency as its resonant (fundamental) one and the higher frequencies as harmonics. So did a vibration analysis engineer who wrote software for me to calculate the resonant frequency of different barrel profiles and bore diameter. They match Varmint Al's mode 1 data very closeVarmint Al has good animations showing 8 modes of barrel resonance from 82 Hz to 4171 Hz that depend on barrel length and mass and moments of inertia.
Thanks for the shock waves speeds
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Bart, if you haven't looked already, you might be interested in Al's analysis of Esten's rifle tuner. He includes the effect of pressure distortion by the propellant gases, which is a factor a resonance calculation alone does not consider. Scroll down far enough in the report and you will see both the bare barrel and the tuner modeled. They did actual shooting to compare to the calculated results.