A little terminology ....
Somewhat counter intuitively, a click is the interval from one number to the next on a Culver conversion style ( which the Harrell's is) powder measure. I believe that the earliest measures of this type only had one detent between numbers. These could only be set at say, 47, 47 1/2, 48, etc. clicks. The Harrell powder measure that I have can be set up to have either 4 or six divisions between numbers. The screws that you referred to are used to create either of these options. I got detailed instructions on how to do this with my measure.
With 6 divisions between the numbers (clicks) each is worth a little less than .1 grain with 133 (.09??) I like having mine set up this way. In my notes, I list the settings between 54 and 55 as 54 1/6, 54 1/3, 54 1/2, and
54 5/6.
Although the fineness of the divisions are a good thing, they have no effect on the accuracy of the measure. That is a function of granule size, and operator technique.
As a practical matter, I find that 133 ,and VV powders of similar grain size, to be the coarsest powders that I will throw directly into cases. It took a long time to come up with a technique to do it, but I can now throw these powders to +- .1 grain.
I have recently bought a small digital scale too verify the weight of measure settings because I am aware that ambient conditions can change the weight of a given volume of powder. Whether holding weight constant when loading at a given temperature/ humidity is the way to go has yet to be verified. That will take some time. If anyone has data on this I would be interested.
