The only dies I have cut have been steel dies and they cut ok with carbide. My shellholder is at .050".
I know you have a new build and want to try it out but perhaps you may want to stop for a minute and ask yourself again "why isn't this working?". Setting the shoulder back a few thousandths more just so the base gets sized enough to chamber is one thing but if you are pushing it back .020" more to get it to chamber then something else seems wrong.
The reason I have a cut back shellholder is because of fooling with other wildcats not the 300/221. In fact I have the 300/221 reamer from PTG which cuts a fairly tight chamber and I have no problem with the Redding dies and standard #10 shellholder. If I FL size brass for that chamber the brass rattles in there and falls out easily if you turn it upside down and that is not with the die turned down to the shellholder. Take a breather before turning your die down. Just my opinion.
Threaded Mode