“you do not want to fill the case so full that seating the bullet compacts the powder”
Study a few reloading manuals and you are bound to discover that *some* powders can be very lightly compressed. Loading density is one the factors that I consider when selecting a powder.
There is a difference between a compressed load and a compacted load. Some people purposely look for a full case load so the powder doesn’t rattle about lose its grain shape.
But you have to agree that 99% of factory loads have air space in the case, which was my point.
The problem with compressed loads is that sometimes they will push the bullet forward over a period of time. This can be a problem if you are feeding them through a magazine...not much of a problem if you are loading single shot.
Dropping your powder very slowly or through a long drop tube will allow it to settle more in the case and you are less likely to need to compress the load.
I shoot benchrest and we use loads so hot that if we drop them into the case quickly they fill it up and occasionally overflow. Dropping the powder slowly solves this problem.