If the barrel has been cleaned properly, and oiled to prevent rusting, I can't see how Pyrodex can possibly ruin a barrel. You need to use a bore brush, and hot water with soap to soak out caked on crud rings, if you let the barrel sit too long before cleaning it. :hmm:
Ask the barrel makers to suggest the best Rate of Twist for your barrel and chosen projectile. They know better than most of us what will work, and they want to have satisfied customers. :hatsoff: