I've used Lee molds and dies for decades with no problems I didn't create myself.
This combo is driving me nuts.
I set seating depth and OAL can vary nearly .010" +/-.
Roughly 1/4 of my loads have to be coaxed to proper seating depth.
I can set the OAL, next few may be fine, next one long...in on the seater a tad...close, but down another touch - .010" under!
Pull it back out a bit, raise the seater a fraction, comes out, say, .010" over - turn the seater in an RCH (AKA a frog's hair) and OAL may come out .010" under again!
Next 2,3 or 4 may come out within a couple thou and then the dance again with more longs or shorts.
Since it's less than 50%, I can't really think the nose cavities could be enough different that one cavity seats fine, the other out of (my) spec but I can't think of anything else to account for it.
Anyone been through this? If not, next casting session I'll segregate the bullets from each cavity and see if, in fact, that's what's going on.
Thanks for lending a virtual ear.