I don't think anyone mentioned the location of the leading. I believe leading predominantly in the breech area may mean velocity that is too low or bullets that are too hard while leading toward the muzzle may mean you are pushing them too hard or the bullet is too soft. I have used Oregon Trail hard cast lead in my .38/.357 and also in several different 1911's (.45 ACP). In all of mine the leading was at the breech end and all but disappeared when I stepped up the loads and also started using liquid ALOX in addition to the OTB lube.

I hope that helps,

Frank

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