I've attached a photo of a boolit (9MM), PC'ed with Smokes Black colored powder, after being covered by Longshot powder for 2 weeks.
The grains of powder are stuck to the boolit and will not shake off.
Apparently, there is some sort of chemical reaction taking place as the powder reacts and sticks to the PC.
Unique, Red Dot, Blue Dot and A1680 have no powder grains that are sticking to the boolit and no visible signs on the PC of a reaction (no discoloration, stains or blemishes that I can discern).
As stated else where, the Unique, RD and BD are older runs of powder, probably from the 80s and 90s. They're what I have and current lots may react differently.
The Unique has been exposed to the PC for about 6 months and the others for about 2 weeks.
This is very unscientific and I don't know how this would effect burn rates, but seems to indicate Longshot may not be a viable powder for PC'ed boolits over the long haul.
I've got a lot of powders, but these are the only powders that I may use with PC'ed boolits, so they're the ones I'm testing.
This throws a monkey wrench in my plans. I was going to start loading Longshot in my 10MM and .40 S&W with plain base, PC'ed boolits. Guess I'll have to go with Unique or Blue Dot or just size and lube with LBT.
It's a shame. A black PC'ed bullet just looks badass to me.