That`s It !!!!
Smokin the cavity with a candle !!
Candles while makes good smoke it puts a film of unwanted petroleum products in with the carbon , even the large kitchen matches have an amount of wax in em to keep dry & promote burnin.
I smoke with a butane also & very lightly when I do , I usually spin a bullet in the cavitys with a paste of comet cleaner to polish burrs & such , try this & cast before smokin the mold .
PS: I have in the past cleaned a smokey mold & got anothe .0015" out of it !!
& fluxing good & keepin clean alloy never hurt either .