I've heard this common wisdom about testing loads by increasing the powder charge by .1 or .2 increments ever since I started reloading. And this has always baffled me.Testing in .1 or .2 increments sounds good too.
How accurate is a beam scale? When the arm and the center mark line up, what sort of margin of error are we talking about? On the electronic scales, the latest ones I have used are accurate only to with .1 of a grain (one tenth). So if you are increasing your powder loadings by .1, there is a margin of error of + or - .1 with EVERY charge you throw.
So realistically, what is the MINIMUM increment you should use that would really mean something? And in real life situations, how critical will that margin of error be anyway? If you use .3 increments and your range of error means you will really be throwing anywhere from .2 to .4 more grains of powder, how critical will that be?