Melting bullets? It's a theory
I doubt the bullet is in contact with the hottest part of the flame long enough to melt.
Mostly I reload .38 & .357. When I load .45, I only have jacketed bullets. I bought some Win231, and someone gave me some Unique and Bullseye, so those are the powders I use. I haven't found a difference in accuracy (up to 25 yards), they all seem to work ok.
Regards.