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lead fouling

  1. Is it lead fouling or just tumble lube & combustion byproducts?

    The 45/70 Govt.
    Pardon my ignorance, but how do I know if it's lead or combustion byproducts? After testing various loads with my cast boolits, I noticed some type of fouling in the last 3" of the barrel. The first 15" looked shiny/bright. It only took scrubbing with 4 patches in the front to get it bright...