Andrew, I'll give you $20 for the barrel NOW.... just send details
It certainly isn't done with, I've personally had my barrel on my SP gun since 1999 and have shot more rounds than I can count or wish to. Using 148BNWC with 3.2AS30. Yeah there is a little bit of lead there after 90 rounds, but I expect that, I didn't like and couldn't get to shoot the 135 grain loads, so I stopped. If you don't want some leading, shoot jacketed and as we both know isn't an option.
I think you are worrying way too much. You could try a slower powder, maybe AP50 but I know people who have a lead mine falling out of their barrels at the end of a SP match, clean it and get on with it.
As you said, it doesn't happen with another gun, right load right gun. My barrel is a 1:6.