I made some pure lead 5.52 slugs today with the MP mold. My technique is clearly improving, since I discarded only about a quarter today, rather than half of them. I was even more critical as well, discarding anything with a visible flaw. The average weight with pure lead is 35.19gr. I tested some with and without running them through the .217 sizing die, and there really wasn't much difference in accuracy. There "might" have been a slight improvement with the un-sized slugs, and they weren't nearly as hard to chamber as the ones I made with wheel weights.
Sadly, my Impact slug liner doesn't seem to like these as well as the NSA slugs, or JSB pellets. I need to do some really careful testing to see just how much worse they are, but I'd bet the group size will be double the NSA at 70 yds.
Rusty