I don't have a clue as to the first part of your post but I can comment on the Redding seating die. I use a RL550B and the Redding Competition seating dieand I love it. I load either 185grJHP or 230grRN. It takes me all of 5 seconds to change the seating depth to dead on accurate for either load. It was well worth the extra bucks that it cost! I am considering buying a 9mm for something different to shoot. You can be assured that if I do, I will get the Redding seating die for it as well.
Hope that helps,