If I had scrubbed the bore clean with something like JB Bore Paste, and then still had problems seating a T/C bullet sabot combination, I would be calling Thompson Center Arms. They are really willing to help you with any problem you might have with one of their rifles.

I own a T/C Black Diamond XR and that thing loads like a dream. I can load and shoot up to five T/C Cheapshots or Shockwaves without swabbing if I really want to.