Ladder test answer sought

[BJung]

I know about the OCW test and I didn't use my chronograph because it was malfunctioning but I have a question I hope someone in this forum can answer.

I conducted a Ladder Tests on Sunday and my prints rose as my charges increased, as expected. But the pattern is sometimes spread out. While I am looking for a horizontal line connecting two holes from loads of a different but consecutive charge, sometimes the holes are farther apart than others. If I were to replicate the loads, the POI would most likely be the same. And so, a charge between these two would be between the two holes. A charge between two holes only 1/2" than 5" apart would be between that. And so, determined load from the average of two holes printing horizontal prints from two consecutive loads with an increased charge of powder, and yet closer together is best, yes?

[ms6852]

Pictures would be nice with your explanation. Don't know about the rest but I'm an old ornery fart that needs to see what your talking about as translation is lost rapidly and perception sets in quickly.

[Bart B.]

One shot doesn't define a group's size (extreme spread) in any direction nor center. Statistics based on 200 to 300 shots in a single group show approximately:

* 40% of the shots are in 40% of the extreme spread. Center 4" diameter circle of a 10" group.
* 30% of the shots are in the next 1.5" band between 4" and 7" diameter.
* 20% of the shots are in the 1 inch wide band between 7" and 9" diameter.
* 10% in the outside 10" extreme spread diameter half inch wide band between 9" and 10" diameter.

What's the odds of a single shot representing where the average of several will go?

[TX Nimrod]

The answer is less than 5%. The sainted “ladder test” is, most of the time, a waste of ammo. Even a single group is not representative of a load’s true accuracy. Shoot four consecutive groups with the same load and tell me they are all the same size.

Statistics is a science, it works. Fool yourself if you want to - and plenty do - but you need multiple groups to definitively discover a load’s actual, repeatable accuracy. Don’t even get me started on “if I do my part”......



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[BJung]

I understand those who are talking about statistics but I take short cuts for the time and money I'm trying to save. You might say it's a waste of time but I'll take the risk. I'll find out the next time I'm at the range, which is probably around Thanksgiving. If not, then a year after that. As I said, I have little time to shoot.

A lot of people use the ladder test. There must be some validity to it. As I recall, I did a ladder test for me M96 Target rifle. With the data, I printed a dime size group at 200 yards two consecutive weeks in a row. I moved onto another rifle after that. I'm not saying your method is the wrong way. In fact, it's probably the right way to do it. I just don't have the time nor patience to wait years to do that way.

[Bart B.]

Yes, lots of people do ladder tests. Few, if any, verify their selected load shoots smaller 20-shot groups than one of several either side incrementally. 3-shot groups typically have a 3X to 4X extreme spread from smallest to the largest and the first one is anywhere in between.

There's another variable I'm not going to mention yet. Some may already know what it is.

What's the biggest group your M96 shot the day those dime size ?-shot ones were shot?

[hounddawg]

I don't have any faith these days in 5 shot test groups other than looking for velocity nodes.

Fool yourself if you want to - and plenty do - but you need multiple groups to definitively discover a load’s actual, repeatable accuracy. Don’t even get me started on “if I do my part”......

[joke]you mean that all bad groups are not caused by ammo/rifle issues ? I am shocked, totally shocked I say [/joke]

[Unclenick]

Originally Posted by burbank Jung

I understand those who are talking about statistics but…

There’s no “but”. The statistics still apply. The only question is, do the stats reveal that you are able to learn enough for your purposes from the shortcut data or not.

…I take short cuts for the time and money I'm trying to save. You might say it's a waste of time but I'll take the risk.

There’s no need for unknown risk. The stats can tell you exactly how much risk you are taking of not learning what you want to know. You have to define it, though.

Just as a faint A.M. radio signal is harder to make out when it is small relative to the static noise that comes with it, what you are trying to discern with a ladder test is the signal (the mean value, aka average value), from the noise (the scattering of shots around the mean point of impact or the scattering of velocities around the mean value or both). How precisely you can make that determination depends on how big the noise is, and upon how much averaging your shot count will let you do to filter out the noise.

In terms of shot placement, you can imagine that if you fired an unlimited number of rounds and the gun never wore down in the process, as your shot count approached infinity, the average result would give you an increasingly exact idea of where your true average point of impact is and how much scatter in location (the noise) will mix with it and tend to displace any particular shot. In turn, this tells you how likely you are to land a shot within a particular range of locations.

As to your current data, if you have enough shots in your ladder, you may be able to learn more than simple eyeballing tells you by separately finding the vertical distance of each shot from the point of aim and performing a 4th order polynomial curve fit to it in Excel (or other spreadsheet program like the Apache Open Office spreadsheet, Calc). This will perform the least-squares fit to the data, which tends to find its trend. The 4th order fit has enough bend directions to find a flat spot. If that doesn’t work, try generating a running average of two and evaluating that result so shot one is averaged with shot two, shot two with shot three, shot three with shot four, etc. If that still doesn’t help, try a three-shot running average, so your data points are the average of shots one, two, and three, and then two, three, and four, and then three, four, and five, etc.

If that still doesn’t bring clarity, you may need to shoot more shots to know what you want to know. How many more can be determined how far apart the shots are on average. I would need to see your data to help you get any more out of it or to determine you can’t know what you want from that little data.

Creighton Audette used single shots of each charge weight in his ladders successfully. You just have to remember the trend of all the shots is being considered, so it isn’t like trying to get data from one shot. On the other hand, he was a champion benchrest competitor and knew how to load to minimize standard deviation and keep conditions for each shot consistent. Not everybody can do that.

[ms6852]

I would like to add something about the ladder test in this case. Burbank you mentioned that you do not get out to the range much because of time constraints. I have no scientific proof on my next comment but base on the fact that you do not shoot frequently I do not really think that a ladder test in your case would be beneficial. Shooting is a skill that diminishes quickly and as infrequently as you shoot it is a good possibility that the poi on your ladder tests could be caused by you the shooter instead of the loads used and the harmonics in your barrel. In this case I would recommend shooting 5 shot groups. I shoot the 5 shot groups at 200 yards because I don't have a range with a longer yardage to do the ladder tests as I wish I could.

Now this just purely speculative on my part. But I know there was a time that I did not go to the range for several months due to complications to eye surgery but when I did shoot I was all over the place with my shooting at 100 yards. This was with a rifle that shoots sub moa 5 shot groups at 200 yards.

[Unclenick]

Depends largely on how much dryfire practice he can squeeze in at home. The rule of thumb we were taught at Gunsite was that if you go more than two weeks without pressing a trigger, your control starts to fade. But dryfire will preserve it. Dryfire has to include assuming the same positions you use when actually shooting.

[Nathan]

Wow! Lots of feedback!

I view it like this. I know the reasonable accuracy expectation if each rifle by the spec of the rifle and quality of components.

For this advice, I’m talking about long range load development at 100 yards. For long range, Velocity sd is as important as raw accuracy. I shoot an initial 10 shot ladder for 2 pieces of data. I’m looking for poi and velocity. I shoot at 10 separate bullseyes. I’m looking at the vert, hor of each impact, especially vert.

People say one shot poi doesn’t matter statistically....and they are right, but in a 1/2 MOA or 1 MOA rifle, the real center point is within 0.25-0.5 MOA, right?

So, when I get 2-3 rounds of a ladder shooting similar velocities at similar poi’s, I need to check that out with a round of ocw, right?

So, I do 3 shot ocw next on like 5-10 charge weights at several nodes....again, I’m using the same assumption that each bullet is within some theoretical distance from center. Then 5 shot ocw. Then 5 groups of 5 across into 5 bullseyes to see what my 25 shot group and chrony data looks like for putting something statistically valuable in the Kestrel.

You may read about the Saterlee method, but it is a PRS, ELR method where bigger raw accuracy is ok to achieve minimum Sd. Under 1000, with factory rifles, we need to worry about raw accuracy. These high end rifles shoot a bad raw accuracy group of like 0.5 in @ 100 and a good raw accuracy group of 0.2” at 100. In my rifles, bad is 1.8” and good is like 0.5”....so aligning s raw accuracy node with an Sd node with a high velocity is required to make hits.

Look up Gavin Trobe on YouTube. He discusses this stuff well. Has good methods, etc.

[Unclenick]

Anyone who hasn't read this Precision Rifle Blog article and who is interested in minimizing velocity changes with load or condition variation should do so.

Regarding the Saterlee method, I'm still trying to figure out why his name is tied to it. Nothing against the fellow, but the velocity flat spot ladders were around long before he came on the scene. There's a good example in the 1995 Precision Shooting Reloading Guide fired by Dave Milosovich who comments it is a phenomenon already long-known to precision shooters at that time. It probably began to be observed when amateur chronographs began to become more commonly available beginning at about the end of the 1970s and into the early 1980s.

[Nathan]

I think the early adopters of the velocity curve flat spot struggled with chrony results. The LabRadar has revolutionized this type of development. Also, early adopters were often thinking 0-300 yds, but Satterlee is really saying you can almost ignore tightening 100 yd groups, if the Sd is right. This is really only true at 1000yds and beyond with super accurate full custom builds, guns which 0.25” at 100 yds would be a bad load.

[Unclenick]

The Oehler optical chronographs and later the CED Millenium do pretty well, as confirmed by Bryan Litz in his testing, and this is how Milosovich made his plot. I love my Labradar, but it isn't essential for this function because, even if the optical chronograph is off a few fps, when you shoot over the same unit without changing its setup and in the same lighting conditions and far enough back from it to avoid muzzle blast effects, it tends to give the same error, percentage-wise, to every round fired in the sample. Thus, you still get a curve that is flat in the right places with respect to charge weight, even if the reported velocity at which it occurs is off a few fps. Litz also likes the Magnetospeed instrument for this.

What the velocity flat spot ladder ignores is how the barrel vibrates in response to recoil moments and pressure distortion of the barrel. We know that vibration's timing matters because barrel tuners work. If it didn't matter, they wouldn't work. The best accuracy will occur when you get a load that has its flat velocity spot in synch with the optimal phase of the barrel vibration. It is unfortunate the late Harold Vaughn's book Rifle Accuracy Facts is out of print. He demonstrated, with some considerable complexity, getting a 270 Winchester sporter to shoot ¼ moa consistently. As part of that, he equipped the muzzle with an accelerometer to detect its motion. In any event, it is the incompleteness of the velocity flat spot as a determining factor for the best accuracy that caused Milosovich to suggest it makes for a good starting point in finding the best load for a gun. A gun will typically shoot better than average in the middle of one, but not necessarily at its very best. If you have a Browning A-bolt or X-bolt with their BOSS tuner at the muzzle, you can demonstrate this to yourself by finding and loading to the middle of a velocity flat spot and then adjusting the tuner to make its groups still smaller.

The problem with using 100-yard groups to tune loads is the lack of bullet drop over that short distance. The 142-grain 0.264" SMK fired at around 2800 fps will show only about 0.09" drop difference at 100 yards with a 50 fps of velocity swing. At 200 yards that grows to 0.4". At 300 yards, it grows another half-inch to 0.9", making it discernable to most folks. Obviously, shooting indoors at 1000 yards would be best, but mostly we can't get to a facility that would make that possible.

Creighton Audette felt 200 yards was good enough for the kind of shooting he did. Randolf Constantine felt 300 was the way to go. Beyond that range, you didn't see much ladder shooting reported before F-class started getting popular for the simple reason that wind deflection is starting to matter at 300 and has becomes a serious factor at 600 and beyond, forcing ladders at long range to be shot in still air or in a very steady wind. For variable wind, you need to know how to take the result of aerodynamic jump out of the equation.

[hounddawg]

a pair of worthwhile articles on statistics in relation to shooting

https://www.autotrickler.com/blog/pr...s-for-shooters

https://www.autotrickler.com/blog/th...-statistically

[BJung]

I have a new computer and can download photos. Here's a picture of my ladder test. Notice, I use $ store bingo markers to compare loads.

My tests are very crude I admit, but the results hasn't left me cussing at myself for wasting my time so far. Maybe this time. I'll shoot again in November and download targets with loads I think where these nodes are. But then, my constraint will be a small sack of handgun test loads, cast bullet test loads, sks test loads, these (with cast bullet test loads), and now my soon-to-be 12 daughter wants to shoot for the first time. She'll shoot .22s.

[Unclenick]

Can't see a picture anywhere.

[BJung]

Thanks for responding Uncle Nick. I thought you guys gave up on me. I'll try again. Anyway, it's a basic ladder test with not follow up. My next step will be to load 10 rounds of each of the loads I think the velocity node is and shoot for groups. If I print a nice group, I'll be happy. If not, I'll start from square one.

[BJung]

I posted the images in the Curio Relic section and cannot delete them so I can post them here.

[hounddawg]

I posted the images in the Curio Relic section and cannot delete them so I can post them here.

https://thefiringline.com/forums/att...0&d=1597119143

here you go Burbank, have to do a run around on the pic. That being said this ladder test is way too busy for me to interpret. Next time maybe use separate targets between bullet changes. Maybe some of the other members can be more helpful

[BJung]

Thanks hounddawk - If you haven't noticed, I used different $ store bingo markers to identify different loads.

[hounddawg]

I noticed that Burbank. My point was doing so many rounds on a single target made the chart too "busy" and for me it was difficult to visually separate the loads for any analysis. That is just how my brain works though, too much on a page confuses me visually. Other posters here may not have that problem and my be able to give you some worthwhile feedback

edit - just did a second look and the 180 gn Hornady load looks like it has nice node from 41.7 to 42.3. Hornady 174 from 42.3 to 43.1 seems to be a node also