So I've been reloading for 8-9 years now. Early on when I reloaded cast in 38 Spl. or 380 Auto, I would sometimes get what I thought was leading. Usually it was just past the throat of the barrel. Copper Chore Boy became my friend. I never had any issues with 357, 45 Auto, or 40 S&W using cast bullets. Very few times in 9mm. Most of these bullets were advertised at 18 bhn.
Then one time I'm using a piece of scrap brass, not brass case, that I ground to a point and a magnifier. I scrape some of fouling out of the rifling. It was packed in the rifling, and would crumble as I scraped it. There was very little lead in the crud. So I came to the conclusion that it must be lube fouling. If I used a slower burning powder, say Silhouette instead of HP-38, and upper load data, I had little to no fouling. So that lead me to believe that the slower burn rate burned up more of the lube.
Now the other day I was reading someones thread on another gun forum and there was a discussion of hardness. A member posted about antimony wash. About the bullet having too much antimony.
And now I loaded up some 200 gr. cast, 95-3-2, using WST powder. These are softer than what I had used before. I had my daughter at the range with me, so I was only able to shoot off 5 rounds. I looked later and seen I have the same fouling as I did in early years.
So could this be what was called antimony wash?
BTW, I'm using Lee's alox lube.