Exactly. I would describe the OCW method as more of an organized trial and error method. Shoot enough groups and you will find what works. My pet peeve is that if you do not measure the velocity and track it to each bullet POI, you are wasting valuable data. That said I have averaged data too, when I really didn't know what I was doing.
Ladders and OCW decipher
- Thread starter Zero333
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Exactly. I would describe the OCW method as more of an organized trial and error method. Shoot enough groups and you will find what works. My pet peeve is that if you do not measure the velocity and track it to each bullet POI, you are wasting valuable data. That said I have averaged data too, when I really didn't know what I was doing.
Sorry but you are confused.
What you quoted is an attempt i.e. “basis” to explain why accuracy nodes are where they are. The explanation has nothing to do with the actual method to determine accuracy nodes. If you don’t like the explanation, fine, explain why the ladder explanation is better or better still come out with an alternative that is better if you can.
However, we don’t use the “basis”/explaination to find accuracy nodes but the actual methods. The two methods use the same rationale i.e. movement of POI to determine where the accuracy nodes are and they work for countless people including me.
This is just so wrong.... No, a simple organized trail and error would involved just shooting 3-5 round groups and choosing the tightest groups. With OCW, you do not choose the powder weight with the tightest groups, that would be a mistake, you choose the powder weight cluster with the least amount of POI movement AND THEN tighten group size with seating depths.
Ok, as a mechanical engineer I am convinced that barrel harmonics is a factor in the performanace of a round. Otherwise it very difficult to explain how rounds of higher velocity impact lower than lower velocity rounds. It is also one of the reason heavy barrels tend to be more accurate than thinner barrels with less stiffness.
I personally have not used OBT since I don't have Quicklaod.
I personally have not used OBT since I don't have Quicklaod.
Ned Ludd
Silver $$ Contributor
There's just one problem with your continuing referrals to OCW and "black magic"...what you're describing now isn't even OCW...it's OBT theory. OCW and OBT are two very different things. As I stated earlier, OCW, which you initially referred to as black magic, is very similar in concept to a ladder test. OBT is a whole different animal. FWIW, even Chris Long himself doesn't make the claim that his OBT theory is the end-all, be-all, 100% correct, mechanistic explanation for what is happening. Fortunately it doesn't matter, because it works, regardless of the explanation. If you don't like the theory, come up with a better explanation of your own that works even half as well. But you might at least want to actually learn the difference between the two approaches first.
Getting ready to do some load testing on a light weight barrel hunting rifle. I have a magneto speed and fear that it will affect the results of a ladder on the thin barrel in order for me to get velocity data. What are your guys thoughts/experience. I thought about running a ladder at 300 with and without so that I could compare.
For sure it would affect the barrel vibration and the results of a ladder test. It would act like a tuner on the barrel. Try to borrow a standard crony and measure the speed of every shot and where it hits the target. Better still if you can get two chronographs put them in series as far out as you can from the barrel (10-12 feet) and get two readings with every shot. If you get a bad reading with one, use the other. If they both look good and close then average them for that shot. I have done this and used to be skeptical about the accuracy of chronographs. I was amazed to see the results of both chronys to be virtually identical, although they do the occasional totally out to lunch number. This converted me to thinking it is the loads that vary from shot to shot, not the chronograph accuracy.
Ned Ludd
Silver $$ Contributor
Ron is spot on about the MagnetoSpeed. Even with heavy barrels, not only can it change the POI, which wouldn't be a problem if it was consistent for all shots, but it can also change group size/shape, sometimes dramatically. I load double the number of rounds, half for MV Determination and half for Grouping. It is definitely more work and components to do it this way, but I feel safer in the long run in terms of correctly interpreting your load development result. Except for this one aspect, I really like the ease of use and reliability of the MagnetoSpeed, which is why I continue to use it. At some point I'll probably break down and get a LabRadar, but haven't done it as yet.
You may like Varmint Al's work, if you have not seen it already. It is very thought provoking if nothing else. I am quite familiar with FEA and it can do amazing things. However, modeling assumptions have to be right on. And the relative amplitudes of response need to be put in perspective. It is extremely easy with FEA modeling to exaggerate the response out of all proportions. Have a look at this page for example. Mode 4 and Mode 8 must be Chris Long's worst nightmare. However, Al does not show the relative amplitude to the fundamental Mode 1 which in my experience dwarfs all the other modes in amplitude.
The other interesting thing about Al's work is that he has concluded that the barrel does not have time in a centerfire to establish the natural frequency modes, and that the relative barrel movement is more influenced by the recoil and chamber firing pressure. Still he concludes that the barrel still does point up, and ideal bullet exit time is when the barrel is rising (not stopped) so that faster bullets exit sooner at a lower angle, and slower bullets exit later at a higher barrel angle. I believe that when the vertical velocity is too high -- probably nearer the straight horizontal position in the sine wave cycle that is when you get the dip in POI with increasing velocity. Your ideal sweet spot will be after that, assuming the bullet is exiting before the natural frequency makes a full cycle.
An Australian Gentleman named Graham Mincham wrote a book called
"Optimum Barrel Length. The Key to Unlocking the Secret of Long Range Rifle Accuracy."
In his book, he outlines doing shorter range testing with 5 shot groups
each with increasing powder loads. Maybe 5 or 6 loads. Do the groups round robin style and through a chrony, but not a Magnetospeed.
Determine the ES of each group as well as POI and group size. The ES will determine the powder load. The group size helps you determine the ideal barrel length. Yes, you may have to cut some off the barrel! If the best load determined by lowest ES also gives best group, no barrel shortening is required and you are done!
I choose to do the ES test as well as the group , but I use a tuner once the powder charge is determined. Then I do a tune at about 200 Yd after checking for change in ES with a couple different jumps. I have not had to change load as the jump I originally used for the ES test was the best ES still. This kind of validates my opinion that tweaking the jump is simply a fine tune which I have accomplished with my ES tune.
I do an additional tune at 1000 yd as well to insure I get the best compensation.
My guns have never shot better!
By the way, I plot my curves of powder charge vs Mv and ES in EXCEL and do a best fit curve fit to 3-5 order polynomial to find true curve to find best load. Incidentally, the prime parameter is not powder load but Velocity. But I don't think you can use best Mv for a different powder as the time vs velocity in the barrel is important for barrel time.
"Optimum Barrel Length. The Key to Unlocking the Secret of Long Range Rifle Accuracy."
In his book, he outlines doing shorter range testing with 5 shot groups
each with increasing powder loads. Maybe 5 or 6 loads. Do the groups round robin style and through a chrony, but not a Magnetospeed.
Determine the ES of each group as well as POI and group size. The ES will determine the powder load. The group size helps you determine the ideal barrel length. Yes, you may have to cut some off the barrel! If the best load determined by lowest ES also gives best group, no barrel shortening is required and you are done!
I choose to do the ES test as well as the group , but I use a tuner once the powder charge is determined. Then I do a tune at about 200 Yd after checking for change in ES with a couple different jumps. I have not had to change load as the jump I originally used for the ES test was the best ES still. This kind of validates my opinion that tweaking the jump is simply a fine tune which I have accomplished with my ES tune.
I do an additional tune at 1000 yd as well to insure I get the best compensation.
My guns have never shot better!
By the way, I plot my curves of powder charge vs Mv and ES in EXCEL and do a best fit curve fit to 3-5 order polynomial to find true curve to find best load. Incidentally, the prime parameter is not powder load but Velocity. But I don't think you can use best Mv for a different powder as the time vs velocity in the barrel is important for barrel time.
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Wouldn't it just be easier and less bullets down the bbl, to find that load.. then find out how fast it is going.. then make your wind charts from that? I don't see the "sense" in "doubling up" loads, having one set for the chrony and another for group development..
Ned Ludd
Silver $$ Contributor
The answer for me is, "No". I am looking first and foremost for optimized combustion. That means the middle of the charge weight window where velocity is least sensitive to minor changes in charge weight, which translates to low ES/SD and minimal temperature sensitivity. This is essential for the long strings of fire (25+ shots) we shoot in F-Class. If you don't determine velocities while testing charge weights, you're really only guessing about the velocity, and primarily using the POI on the target (or groups) to define optimal charge weight. On plenty of occasions I have observed where the best grouping during charge weight testing was not in the optimal charge weight window. However, that is a relatively easy fix. Once I have identified the middle of the optimal charge weight window, I then tune the groups using seating depth adjustments. Obviously there are a number of load development approaches that can allow you to end up at basically the same spot. This is the approach I prefer and it has worked very well for me.
Got to get yourself a LabRadar Gstaylorg...
It's super!
i don't look at "groups", i look at the vertical dispersion..
gstaylord,
Right on about Mv being the important metric!
The theory is that there are two oscillatory functions going on. One we call the traveling doughnut where the barrel acts like an organ tube with oscillations going up and down the barrel at the speed of sound in steel till it gets to the muzzle and reverses as the barrel is open. This creates a microscopic cinch due to slightly smaller inner diameter traveling up the barrel. This function is not terribly bothered by a Magnetospeed. As I further tune the second function with a tuner, I do the first metric with my Magnetospeed.
Second oscillation is the barrel acting like a beam and wiggles up and down with anywhere from one to more cycles in the barrel length. These oscillations cause the barrel to point up and down as a function of the frequency of oscillation. This one is screwed up by the weight of the magnetospeed. If the load for best beam frequency matches that for best "traveling doughnut" you are done and the barrel length matches both. Otherwise you would alter the barrel length to make the beam oscillation and doughnut oscillation match.
I just find best doughnut oscillation ( load/MV) for best ES and then tune the tuner for best group. I do the load test with the tuner adjusted all the way back toward the action then shoot 5 shot groups at each tuner setting (initially 1/20 turn per group for 5-6 groups.
Both the ES and group data points are plotted in EXCEL with 3 to 5 power Polynomial curve fitting equations so the data closely matches the curve and then find actual calculated minimum of ES and group size vs load
Why do I use 5 shot groups? They do not tell the complete story, but are so much better than 2 or 3 shot groups that you actually save bullets doing 5 shot groups.
If you then change powder, you start over as different powders have different rate of change of velocity down the barrel so you can have two powders with same Mv but different Barrel time.
Right on about Mv being the important metric!
The theory is that there are two oscillatory functions going on. One we call the traveling doughnut where the barrel acts like an organ tube with oscillations going up and down the barrel at the speed of sound in steel till it gets to the muzzle and reverses as the barrel is open. This creates a microscopic cinch due to slightly smaller inner diameter traveling up the barrel. This function is not terribly bothered by a Magnetospeed. As I further tune the second function with a tuner, I do the first metric with my Magnetospeed.
Second oscillation is the barrel acting like a beam and wiggles up and down with anywhere from one to more cycles in the barrel length. These oscillations cause the barrel to point up and down as a function of the frequency of oscillation. This one is screwed up by the weight of the magnetospeed. If the load for best beam frequency matches that for best "traveling doughnut" you are done and the barrel length matches both. Otherwise you would alter the barrel length to make the beam oscillation and doughnut oscillation match.
I just find best doughnut oscillation ( load/MV) for best ES and then tune the tuner for best group. I do the load test with the tuner adjusted all the way back toward the action then shoot 5 shot groups at each tuner setting (initially 1/20 turn per group for 5-6 groups.
Both the ES and group data points are plotted in EXCEL with 3 to 5 power Polynomial curve fitting equations so the data closely matches the curve and then find actual calculated minimum of ES and group size vs load
Why do I use 5 shot groups? They do not tell the complete story, but are so much better than 2 or 3 shot groups that you actually save bullets doing 5 shot groups.
If you then change powder, you start over as different powders have different rate of change of velocity down the barrel so you can have two powders with same Mv but different Barrel time.
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