I have heard that phrase many time on here. Dry tumble works for most....not for some.
I found an interesting thing today. I was BBDT'ing a bunch of 40 175TC slugs and while waiting outside my shop for the bake to ding, I found four 9mm slugs on the patio I had dropped last week. They had been laying there since then and we had some rain. I just threw them in with the next batch.
POWDER WOULD NOT STICK AT ALL!!!!!! ZERO. ZIP. NADA. The 9's looked perfectly clean and shiny, but there must have been some oxide or something formed on there that prevented any static and cling. Not a bit of powder would stick. And it was Smoke's blue!
So.........from what I discovered......do NOT try to coat old boolits unless you clean them with laq thinner or mabe even vibrate them for a few minutes in new clean walnut shells. I always PC my slugs the next day after casting and store them in ZipLok bags until coated.
I have stripped old grease lube and coated many hundreds of old boolits in the past with PC......but all were soaked/washed well in laq thinner and then rinsed in Simple Green and VERY hot water.
Hopelfully this info may help those out there that are having coating problems.