Just wondering, are you using the Brinell 12's or Brinell 18's?

I use the MBC Hitek 12's in my .38 Special loads, and low end .357 loads, 800fps-900fps, The .38 level loads do not give me any leading at all. I use the Hitek 18's in my 9mm, and hotter .357 loads, 1000fps -1200fps. I do get an accumulation of "lead" with the 18's @ 1200fps after about 75 rounds at the upper end of the velocity range, but no loss of accuracy over 100 rounds. At 1000fps, no leading at all. I wasn't shocked or disappointed, as they are about the same as the Berry's plated bullets. They cost less.

I use Red Dot for the mild loads, and Unique or Herco for the 9mm and heavier .357 loads.