In the time I have been testing these shenanigans, when a sharp throat was encountered that tended to shave our precious .001-.002 oversized coated bullets, leading showed up. Oddly it was in the end of the barrel and appeared remarkably similar to traditional lube running out. Neat. That could be over come by switching to a bullet design with a less sharp, or smooth, transition to full diameter like a WFN, WLN. LSWC were no bueno with a sharp throat.
Most interesting. I have chased this around a bit , but doing so totally clueless. So possibly a round nose bullet would be exactly opposite of a sharp edged swc???