Useless Information

The original ladder test was created by Creighton Audette. I can't find the original article, but I did find Incremental Load Development Method by Randolph Constantine.

Randolph refers directly to the Audette method, which he uses. Five pages in, it becomes clear that the test is about tuning barrel harmonics by changing the powder charge.

The Creighton Audette ladder test uses incrementally increasing loads of powder all shot to the same point of aim, which produce a rising string of shots on target. There is much said in interpretation on the observed convergence of several points of impact. It does not mention seating depth at all.

The observed convergence around a particular point on the target is where the barrel harmonics reverse, and is not indicative by itself of an accurate load. All that has been demonstrated is a change in barrel harmonics with a change in powder charge.

There is no documented attempt that successfully duplicates the result of any ladder test.

There is a low probability of finding an accurate load using this method. Randolph Constantine observed "the number of rounds you have to fire before you find a good load can be a significant percentage of your accurate barrel life". He should have added, "if ever" somewhere, because this particular process is so hit and miss, you could shoot the barrel out before finding a good load.

This is a ladder test that involves single shots of increasing charge weight, some will say it takes 10 shots, some 20, and it looks for velocity flat spots.

It's a waste of time and components.

Plotting the velocity for each shot may or may not show one or more "velocity flat spots". Those may or may not correspond to the change in barrel harmonics, most often they do not. What is the cause ? An increase in powder that does not show a corresponding increase in velocity below the max load is a problem, not a solution to anything.

My guess is the cause of the velocity "flat spots" is a convergence of the normal variables.

Statistically, velocity is within the sample range. If your one shot of the lower charge gives you the higher end of its velocity range, and the next load of the next higher charge gives you the low end of its velocity range, then you have what looks like a flat spot. If something like that occurs with 3 loads, the first near its high, the second on its mean and the third on its low, then you have a really flat spot. Which will not be immediately repeatable.

Besides the total absence of any meaningful result, my reservations on the interpretation of this ladder test is due to the fact that no particular ladder test has ever been repeated at a different time with the same result. Myriads of people have made innumerable results of their ladder test public, and postulated as to the merits of their conclusions, but not a single one has ever gone on to repeat the test at a different time, and gotten the same result. It may be argued that no two ladder tests can be exactly the same, in which case it cannot be called a test.

Why are there alleged velocity flat spots on the ladder test ? Opinions abound, but nobody really knows. Common opinion says that's where the load needs to be. In spite of the fact that the alleged flat spots on the ladder test may not correspond to an accurate load. Or anything definitive and constructive. Yet the ladder test remains popular.

You do not need to ladder test for powder charge. You need to find a low ES powder charge and a small group over at least three shots, which you can't do with this kind of ladder test shooting one round with one charge, but you can if you start with the OCW method.