Yes, i have heard the same thing, but my personal experience differs. Four of my rifles rusted using Blackhorn powder, and leaving the burnt residue in the barrel without cleaning. They all only had minor pitting, but it was/is always there. Two are now worn out; one i sold. One is a CVA.

Myself, i just cannot hunt a whole season with a powder fouled barrel. Primer fouling is non-corrosive. Blackhorn burnt, is corrosive.