Carbon. Soak with Kroil to get under it so to speak or ability to loosen.
JB and even diamond lap paste are a main stay if I have issues. Not at all afraid to use them. Cannot ever say they have harmed a gun in relation to barrel life or accuracy. They usually bring it back, but if its at the end of its life then its kinda 50/50.
End of life I do find that, and I think chrono's are overrated generally, if I shoot over a chrono I've lost speed and hence may not be in the sweet spot so need to ad powder and possibly bullet seating depth if thats possible.
I have never tried the fire lap bullets. FWIW.
