I agree with
@snert , if you are using a delicate seating stem, and you observe the base of the bullet is compressing the load, you should learn the techniques that help settle the powder. This helps avoid damage to the seater and seating depth issues. I recall flaring and ruining my very first Redding seater stem that way.
I have no idea if crunching a powder charge creates additional combustion issues, but it certainly has caused ES/SD issues for me. I try to avoid hot loads, but in the past I had some REM 700 factory bbls for hunting that liked the higher nodes. I learned that the ones where I settled the powder before seating shot the same average speed, but with a much tighter SD/ES.
I have no explaination for the differences, but they were repeatable. Could it be due to seating issues caused by compressed powder… I don’t know, but seating depth and runout were also noticeable problems with compressed loads and another good reason to grab a drop tube or toothbrush and play with it to learn which methods (or both) works best for you.
The toothbrush needs a comment… a vibrating battery powered toothbrush can often get lucky in terms of hitting the right frequency note to settle powder, so you will also want to play with different lengths of drop tube and give a toothbrush a try some time too. To observe this, just throw the powder in a case where you can watch the neck, and touch an electric toothbrush to the case and watch to see how well it settles.
At least one time in your reloading journey, you will probably want to study a favorite caliber. For instance, a 6mm BR or a Dasher? How much powder capacity and given seating depth for a given bullet?
The easy way to study this uses a sample of a fire formed case and a virgin case, both with an expanded neck that allows the bullet to slip when pulled or pushed by hand, but not sloppy. You can then slide that bullet in by hand till is stops on the powder.
You can then play with a bullet comparator and your powder fill versus seating depths to learn if your drop tube technique works. You will also learn the exact capacity and fill ratio for your situation.
I keep plots of charge versus seating depth to compression of those calibers so I know ahead of time how to have a chamber throated to avoid compression issues.