I am shooting a 5"m&p with a storm lake barrel. I am using wheel weight lead. I do not have a hardness tester. I am getting some leading, but does not seem to hurt accuracy. The bore has a greyish look to it, but I think it is moly residue. I am tumble lubing by hand, air -drying for 30 minutes, then baking for an hour after they come up to temperature. I am still learning. The load is chronographed at 1070fps.