I am wondering if someone can point me to a solution to a problem I'm having with my CBs. I am casting bullets from range scrap, adding a couple of ounces of tin to a 10lb pot so that I am casting bullets with an approximate BHN of 12. My CBs are cast from RCBS 38-148WC and RCBS 38-158CM molds. I shoot them out of a GP100, the chamber throats have been reamed (thanks DougGuy) and measure .358, and this is what I size the CBs to. The forcing cone has been given an 11deg bevel.
I load these bullets over 3.5, 4 or 5 grains of Red Dot in either 38 special or .357 brass. They are tumble lubed with 45-45-10. It is inevitably the case that the wadcutters lead very little, but the RNFP leads my barrel a lot. In addition, the area around the forcing cone gets painted with lead and I even get leading on the outside of the cylinder. (I have no pics at the moment but will have to remedy this soon). The velocity of the loads do not exceed 1000fps, so we are not talking hot loads here and the BHN of the bullet should be well within tolerances for such light loads without requiring a gas check. What would be the cause of this? I find it odd that similarly sized bullets would have such different results. Does the shape of the bullet make a difference? I've tried sizing the bullets up to .359 and down to .357, but get similar results.