A couple items....maybe pertinent.
Regarding extreme spread the ONLY way to bring it way down is to weigh each individual load.... for starters. Once every load is a weighed charge, not a thrown charge, THEN there are some tricks ........ but the basic rule is, weigh every load.
On this note. For many years I only weighed the charges while working up the load. I'd write down everything, set the thrower where I wanted to be and throw my bulk charges.
2 things happened: #1, I never could get the ES down like others and #2 I was all'atime getting unexplained over-pressures and hot loads.
It wasn't until I started routinely WEIGHING everything that it really was driven home that powder throwers ARE NOT ACCURATE ENOUGH for loading to the top of the load workup. Unless you use only ball powder you MUST weigh everything when attempting to run near the top of the scale.
I've tested many throwers.
MANY people here on BRC have tested MANY powder throwers.
These and others' tests have been written up here and elsewhere for 15yrs now......
The results are unanimous, don't trust the thrower when running hot and rermember that the powder thrower is very much affected by technique. A person can expect as much as a full grain of difference in his throw from session to session and onl;y scrupulous technique coupled with a short-grained powder will keep you within a half-grain on any given day.
As I said, maybe pertinent, maybe not but it's 2 more sense!
50 of these and you'll have a dollar....
al