When shooting (lots of cast) and I do! 7mmtcu , 7mm rimmed international 7 0/8, 30/30, 303 br 30 herrett 38spec, 357 mag ,357 herrett, 357 max, 44 mag, 445 supermag, 45 acp most running at or above 1900-2000 fps and I experience little to no leading . With proper boolit fit ( 1-2 thou over groove diameter) and a quality lube with gas checks where requiered, Most if not all will find that a properly cleaned barrell ( free of all the redskin fouling ) is just like your mom's/grandmom's old cast iron frying pans, They dont even work right untill they are seasoned! Just a quick wipe with a dry pach or two then a VERY light wipe with an oily patch to prevent corrotion and put em away. This is just my opinion and I have only fired 15-20 000 cast boolits out of my firearms over the last couple of years so yor results may vary!