Thread: Load development / Ladder test

ebf, with your factory load example the variable of interest is just the brand, A, B, or C. In this case I would shoot as many as I can afford to use, one target per type as you plan to do keeps the results separate. The more you shoot though the more statistically significant will be the differences in the observed size of each group. Letting the barrel cool between shots as time allows minimises a possible cause of POI change as you indicated.

For your example with factory ammo it is group size that is of interest. With OCW it is the movement in the average POI that is being looked at. “Round Robin” is just an averaging tool.

Taking these shots in a Round Robin ( A,B,C,A,B,C etc) is intended to average out some non-random changes in POIs that are not linked to the variation in the ammunition being investigated (be it brand, powder weight, seating depth etc. ) - these might be changes in your "set-up" at the bench between shots or groups of shots, progressive shooter fatigue, fouling of the barrel and so on.

The reverse side is that if using a Round Robin to test different factory loads there may (note: may) be interaction between the the different brands as you cycle round them since you would be mixing powder type and jacket material. This does not apply for OCW where bullet and powder are constants. So possible pros&cons either way. I might be inclined to pass up on the round robin altogether and instead start with a clean barrel for Brand-A, shoot 2-3 foulers and then your group, thoroughly clean the barrel for powder & copper and repeat for brand B, repeat again for brand C. Provided you don’t end up shooting one load “better” than the others it could be a way of giving each load a fair crack. Just a thought.

The Optimum Charge Weight method as the name indicates is really for developing hand loads where the powder charge is being varied (also good for seating depth with barrel time typically fixed) and where this exit time-to-barrel vibration relationship can be optimised to minimise the effect of reloading tolerances.

With a given factory load the shooter has no control over when the bullet leaves the barrel in relation to any stationary points or “nodes” in the flexing of the barrel so OCW cannot be applied. With different loads each type will likely exit with different barrel times having also excited vibrational differences in the barrel, and there will be a component of the overall group size resulting as a function of this with the consistency of the ammo (what OCW is looking at). The resulting average POI for groups with each type will probably also be different, but then you haven’t just changed one variable by changing ammo types. The group size will typically be dominated by the other factors that determine whether a rifle “likes” a particular load and of course shooting ability. I mention this only because in my case poor shooting skills limit the extent of any load development I can achieve so I have to be content with understanding the theory without being able to put it into practice.