I saw John Benjamin a few times at machinery auctions. He would drive up to the greater Seattle area from the Portland area. He makes premium barrels all by himself.
I was talking about the 30-06 black tip AP bullets were producing better groups for me than Match Kings. He said those AP are bad for barrels.
He is a top state level competitor in high power, and I am just another guy at the range. What would be bad for his barrel might be so subtle, I would never know the difference in mine.