Update:
RCBS dude confirmed over phone, but would not provide a print: their die shoulder diameter is .465”. That seems very weird to both of us so he wrote his Engineering team to find out if it’s correct and why they chose it - standard answer is “Saami spec”. This isn’t Saami cartridge so not sure how it was decided.
Amazon had Redding type S die same day shipping for 6 dasher with free return.
Just dropped a fired case in. Bottomed out on my shell holder it bumps case datum back .0035”, and resizes shoulder diameter to .455”. Sized case chambers easily. I’ll just back off to .001” for bumping the rest of the cases.
I’m probably going to move on at this point with the Redding die.
But - On principle I’ll figure out what the heck is going on with the RCBS die - literally no one could use it in any dasher chamber. Missing something and I’ll try to get to bottom of it.