Partial bullet sizing to fit the throat is to be considered, since the desired (major) bullet diameter inside the case is to be 0.512".
I really wish I had used a "coned-up" breech like on the .458 WinMag.
No worries with that sort of throat.
Might need a new throat reamer, or maybe even a neck and throat reamer.
Anyway, the rifle is going to look something like this when shootable: