Originally Posted by Taterhead
As I mentioned earlier, you could "calibrate" a homemade dipper, but different lots of powders can have different densities.
Example: Just last weekend, I ran ran out of powder from one lot. I refilled the hopper after empty with a new lot of the same powder and did all the usual measures to settle it, etc. (I do not mix lots). The new lot threw 2 tenths heavier because it was more dense. 2/10 wasn't a too terribly big deal with the slower burning powder I was using, but it could be a big deal if using a fast burner. I weighed on the scale and "re-calibrated" the throw by turning it down to a smaller volume.
Correct, you have to have some margin. the table that comes with Lee dies shows only start loads for the dipper. It will show powder X with the dipper and say a 180 grain bullet as a start load of 4.0 grains and the dipper throwing 3.9, then it will show a max of 4.9 of the same powder with no dipper recommended for a max.