Re: Can I tumble brass thats already primed?
Media crumbs in flash holes are probably the main cause (after forgetting to add the powder) for misfires with reloads. Once the primer is seated, it's too late to tumble the empty cases. In fact, I always look for light through the flash hole before I seat my primers. Prevented quite a few misfires that way, I firmly believe.
Sooty necks will A) disappoint the purist) and B) may mislead a shooter (after firing) to believe they might have an underpressure issue, and C) may make some small contribution to getting a chamber marginally dirtier.
If they bother you, polish the necks with steel wool once the bullets have been seated. Bore solvent may remove the soot, but may also have ammonia in it, which probably isn't recommended for use on brass.
Greg