Well, I said I would share some first hand stuff about what I've learned. I'm gonna take the easy way out. This link takes you to Hornady's website and the page it loads is word for word what I have in my Hornady manual. The graphics do a much better job of explaining what is printed.
In a nutshell, I have done everything by the book. Some details yeild impressive results, others, well, It can't hurt.
1. Sorting cases by manufacturer, My rifle don't seem to care.
2. fire formed brass, WOW, I use casings fired from my chamber and neck size only with a Lee collet die. These 2 adjustments made more difference than all others combined. It only works for bolt action rifles with a properly functioning extractor. (no they don't get stuck, but an auto wants to yank the expanded cartrige out before it can cool and retract. The cooling and retraction are fast enough to be of no consequense to a bolt action shooter but not as fast as an auto action cycling)
3. trimming cases, I did find a measurable difference at the range. I always measured my cases after resizing and found them to be "in tolerance" and didn't trim. When I decided to trim and de-burr the mouth I found an appreciable increase in accuracy. I think the de-burring lets the jacket of the bullet glide in when being seated therefore you have no jacket scarring which can upset balance.
4. Bullet seating depth, boy did I spend a lot of time on this one! Load 5, go shoot. Load 5, go shoot. on and on. I think it was worth it. Measurable difference at the range from .002" difference in overall length. But you still gotta load 'em in the mag! That one bit me, once!
5. Powder dump, Iv'e said before, for my rifles I weigh every charge for every cartrige. I adjust the dump to get me as close as possible every time and normally add or remove granules at the scale. EXACT same charge time after time.
The truth, the whole truth and nothing but the truth!