Ladder test

[Jowens]

Here is several shots I loaded up to check velocity and pressure with varget and 155 scenars. Half grain increments 45 to 47.5 grains. This was done at 300 yards. Can anyone gather anything from it? Mqybe the range wasn't far enough, half grain increments too much, Ect.

 

[rsplante]

There are several methods of conducting a ladder test. It looks like you are performing an "Audette" ladder test. I personally do not like the Audette ladder test as it relies on a single shot at each charge weight. That means that all of your results depend on you making perfect shots. Not only must you make a perfect shot, but no other variable can be allowed to change (barrel heating up, wind speed/direction changing, you getting fatigued, lighting changes, barrel fouling, etc.)

One method I have found that reduces the effect of human error is to use separate targets for each charge weight and shoot one shot from the first charge weight, then the second target with a round from the second charge weight, etc. This way, you not only have several shots representing each charge weight which you can average, but the above mentioned changes are spread out evenly among the different charge weights. Because of my equipment, I can no longer use this method for reasons I will explain.

Since a ladder test can be expensive, I want to gain as much data as possible while conducting the test. As a result, I not only look at the target results, I also chronograph my ladder tests. My latest chronograph is an Oehler 35P Proof Chronograph. While the 35P is a superior instrument, the software is a little behind the times. You cannot change shot groups like my previous cheapie chronograph. That means that I must shoot all shots for each group as a single group if I want it to calculate the statistics (high speed, low speed, spread, mean, and Standard Deviation).

What I have settled on as a ladder test, which works with my equipment, is to shoot 10 shots at each charge weight, using a different target for each charge weight. Since I am looking for consistency in exterior ballistics based on the charge weight, my understanding is that I should ignore windage. ( I have recently been informed by a benchrest shooter at my range that the wind can have an effect on my vertical spread if it is blowing directly at me or directly away, presumably due to a change in relative velocity, i.e. air speed instead of ground speed.) In any event, I look for the minimum vertical grouping.

Hope this helps.

 

[rsplante]

Oh, on rereading my response, I found that I left out some data. In my second paragraph, while describing a ladder test where I progress from target to target with one shot in each, I neglected to mention that I eventually fire 5 rounds at each target by cycling through the targets 5 times. Also, here is a link to my source for that method:

OCW Overview - Dan Newberry's OCW Load Development System

 

[devildogandboy]

it doesn't sound like you followed this step exactly. if you did you would have fired shots of the same grainage all on one target, then the next target would have the same grainage + .5 grain and so forth for the remaining targets. I hope this makes sense as I am explaining it.


11. After you have fired the sighters and confirmed that there are no pressure signs (hard bolt lift, flattened primers, etc.) you allow the barrel to cool for an adequate amount of time (use common sense--the hotter it is outside, the longer it will need to cool) you will then fire your first shot from the first group of the graduated charges. You fire this shot at target number 1.

12. Allow the barrel to cool, then fire a shot from the second graduation at target number 2. Wait for cooling of the barrel, then fire a shot from the third graduation at target number 3. Continue this "round robin" sequence until you have been through all of the targets three times. At this point you will have a three shot group on each of the targets.

 

[scudzuki]

Oh, on rereading my response, I found that I left out some data. In my second paragraph, while describing a ladder test where I progress from target to target with one shot in each, I neglected to mention that I eventually fire 5 rounds at each target by cycling through the targets 5 times. Also, here is a link to my source for that method:

OCW Overview - Dan Newberry's OCW Load Development System

What you are doing is an OCW test, not a ladder.
I understand why you have modified the procedure but I wouldn't do it that way despite its advantage since it may skew the results. Minimizing the effects of barrel heat and fouling, atmospheric changes, shooter fatigue, etc., is of the major benefits of the procedure. Can't you just record the speed of the individual shots and calculate the ES afterwards?

Joe

 

[VKC]

I could be missing something but depending on the scale of the target, it looks like you should just go with 46gr and forgot about it. That's a good group at 300 yards

 

[rsplante]

Can't you just record the speed of the individual shots and calculate the ES afterwards?

Joe

Yeah, I guess you are right. Just lazy I suppose. Standard Deviation is a pain to calculate manually, plus there is the idea that if I get "Off" by one round in my shooting OR recording, the entire test could be in jeopardy. I HAVE done it that way once before, maybe I'll just have to focus on accurately recording each and every shot.