+1 Lee Factory crimp die.
In jacketed I flare the case mouth just enough to get the projectile started for seating. That ensures the case grips the projectile well.
For cast you'll want a bit more flare, or seating will shave the projectile as it is seated. The Lee FCD in either circumstance will ensure the case mouth
is returned to a more normal profile.
The dummy should be able to drop with just its own weight completely into the chamber, and fall out again with just it's own weight if you "pour" it back out of the chamber again.
Within the constraints I laid out earlier, longer projectile seating tends to be better, as it also reduces pressures for a given amount of powder.
The specified clearance allows for fouling buildup and production dimensional tolerances.
Check the OAL of your dummy with your micrometer, try pushing it against a soft piece of supported wood, and re-check the OAL. It should still be the same,
which means the case is griping the projectile tight enough. That also ensures that the feeding cycle from the magazine won't be pushing the projectiles
further into the case, which raises pressures for a given quantity of powder.
A little extra effort in getting the dummies set up right will avoid chambering issues later, especially failure to go into battery
(slide not closing completely on a chambered round).
