Many modern bench rest shooters today, will not use them for fear of harming their 4140 and 4150 or Stainless 416 match barrels.
I cannot "see" nor understand any reason for their use in our ML barrels, even though our barrels are likely much softer and prone to
any adverse reactions to misuse, if indeed, the use of bronze brushes is misuse. I stopped using bronze brushes back in the 70's in
my modern match barrels as well. I was capable of understanding and accepting on faith, that the "experts" in the field of competition
who were willing to share their learned knowledge were not steering me/us asunder.