Just loaded 20 rounds using the #10 RCBS shell holder. If I pulled the handle down too far I could feel "something happening" to the case. Upon examination the smiley face was about to occur by seeing the beginning of damage to the case mouth. But if I took it easy and pulled up just after the powder drop everything went well. I don't think the RCBS shell holder is any better than the Lee. May try the Lee expander plug with the M step. But If I go slow at an even pace I should be OK for now. I don't load in volume so gong slow is fine.
See post #39 and #49