Load Development - The Ladder Method

[Ganderite]

One of the most experienced, logical and sharing guys I ever had the pleasure of meeting was Creighton Audette. He did a lot of testing and load development. He was downright insulted by any talk of an accurate rifle or load that was not supported by multiple 10 shot groups. He seemd to have a very strong grasp of statistics.

The ladder method involves loading the test ammo in small powder increments from the Start Load to the Max load, but ONLY ONE SHOT PER LOAD and then shooting the entire string at one target, preferably at 300 yards or beyond. The result will be a string of shots up the target, with the mild ones at the bottom and the hot ones at the top.

To start the test, fire some fouling shots of the first (mildest load) to warm the barrel and to zero the rifle so it starts the group at the bottom of the paper.

But the string will clump at one or two places. The clumps will be caused by the barrel harmonics. These are then the loads to concentrate on for load development.

Here is a detailed article on the technique:

http://www.lima-wiederladetechnik.de/Englisch/Laddertest.htm

 

[thunderflash]

Just had a quick look at the site --looks to be a very interesting study over a cup o' caffeine! -- Thanks !!

 

[Ruthless]

Neat I'll try that as I don't feel like wasting 20-30 pills from each box (lapua, Sierra, Hornady)

 

[Scar270]

That makes some sense, find where your rifle is forgiving on the exact powder charge too.

 

[msg.drew]

leave it up to the germans they will figure it out... looks very interesting... wonder if it works for pistols too?

 

[Obtunded]

I've been ladder testing for a long time and I am convinced it is the way to develop a load. You MUST use long distances to get the maximum benefit and this means shooting in very good conditions though. (I tried ladder testing a 6BR recently at 160 yards with a new Krieger barrel... from 29 - 31.6 grains of varget in .2 gr increments, I had 1 ragged hole under an inch across! )

 

[Trevor60]

I have used the ladder test a few times like when i changed lot# on powder and I don't mind windy conditions if it is coming for the 3-9 positions it the 12- 6 wind that screws up the readings. Shooting out to 300 hundred allows you to see which loads are holding vertical and which loads are showing elevation it a great tool.

My only other suggestion would be to shoot at the smallest target you can comfortable see. By shooting at a small target you remove the possibility that you are influencing the vertical which may lead you to dismiss a load that works for the gun.

 

[kombayotch]

Chris Long actually came up with a model for various barrel lengths that predicts those node.

http://www.the-long-family.com/OBT_paper.htm

This spawn the development of the Optimum Charge Weight (OCW) method of load development:

http://www.clik.to/optimalchargeweight

Long has some nice app notes on predicting the barrel times for various loads using Quickload:

http://www.the-long-family.com/optimal barrel time.htm

And with a pressure trace system, you can actually measure the barrel time:

http://www.shootingsoftware.com/barrel.htm

It would be interesting to compare the OCW to the Ladder method.

 

[lineofsight]

Great timing, three more weeks and will start some load development. Was planning on OCW method, will read these other and maybe take a "gander" at an other one too.

 

[CyaN1de]

I have been palying with Quickload and the OBT method on my PC the last few weeks.

Running an accurate known load through QL gives me near identical OBT numbers as is shown in the OBT Excel file which tells me there is something to this.

 

[kombayotch]

It would be interesting to compare the OCW to the Ladder method.

I started thinking about this and came up with a better idea: Instead of comparing them, how about combining them?

I really like the graphical aspects of the ladder method. However, I really find it lacking with just shooting one round of each weight. And its a PITA to keep track of them.

The OCW method takes away a lot of randomness since your are firing three rounds (I think five would be better, but 3 is ok). What I don't like about it is that the analysis method involved eyeballing the targets or comparing numerical values. Just looking at the x,y numbers and the targets doesn't really tell the whole story. Also, since you're taking 0.3 gr. steps, you aren't perhaps taking the most ideal charge weight.

Now, theres a nice little free piece of software out there called "OnTarget" that lets you analyze pictures of your targets and extract things like group size and x-y distance from point-of-aim.

http://www.ontargetshooting.com/download.html


It gives you something like this:

OCW target #1

OCW target #2


Well, if you take all of the x-y coordinates it spits out and plot them to a graph in Excel, you get a pretty interesting result:

You basically get the Audette ladder, BUT with multi-round groups.

With this, I think it is easier to pinpoint the OCW to 0.1 gr. Plus, it gives you a nice graphical representation of how your barrel is whipping, without all of the hassles of the Audette method.

 

[kombayotch]

Here is the load with RL-17 and Lapua brass:

A subset using Hornady brass in the area QL predicted:

 

[kombayotch]

I put all three on the same graph and normalized the scale to 0.1"x0.1".

I believe results would be cleaner with 5 shot groups.


Here were the RL-17 groups:

Old one from my first outing with RL-17

 

[looch]

This thread is going into my bench binder.

 

[looch]

Okay, so I thought about this over the weekend and I'm having some conceptual difficulties. Please try not to be too stunned by my MS Paint awesomeness:

Am I to understand that in OCW terms, loads/targets 1, 2, and 5 would be more desirable than 3, 4, and 6?

There's a joke I heard about two statisticians that were duck hunting. Edited to get to the point: One stands up and shoots at a duck and misses, 1' to the left. He takes a 2nd shot and misses again, 1' to the right. The other statistician starts jumping up and down yelling "You got him! You got him!"

 

[kombayotch]

No, the position relative to the origin is not what determines the best charge. The OCW theory is that after the scatter group, the OCW zone is about 0.7gr. above it (in 308). After the scatter group, you should see 3 groups that have approximately the same center locations relative to the point of aim. So, 3, 4 and 6 would be the desireable ones. You would idealily choose the charge weight that corresponds to the middle charge of that group, but do not include the scatter group.

For the above OCW sequence, that would mean the 45.8 gr. group. This sequence is shown as the red trace in the combined chart. Notice that the pattern and location is nearly the same even when I use a different brand of brass (and compensate for the difference in case capacity).

 

[kombayotch]

Wait, are those supposed to be center point plots or shot groups? I had assumed center point plots...

 

[looch]

After the scatter group, you should see 3 groups that have approximately the same center locations relative to the point of aim. So, 3, 4 and 6 would be the desireable ones.

This is where I'm getting lost. 1, 2, and 5 are the groups that have the same center locations relative to the point of aim, not 3, 4, and 6.

Edit: Sorry - the red dots in my diagram represent (by my eye) the average POI.

 

[kombayotch]

The red dot would not be the point of aim, it would be the center of the group. Assume that your scope is not zeroed while you're doing this. The point of aim would be (0,0), the origin. Also, you need to look at the charges in sequence, not as individual groups. Its a sequence of groups that show the pattern, not one individual group.

 

[kombayotch]

Ok, I read your last post again, these are shot groups....

Again, what you drew doesn't really represent the test or the results.