The sabot takes care of the bullet to barrel interface. No need for lube or gas check. The bottom of the sabot is the gas check and the sidewalls both grab the bullet to impart spin and also seal off the gases. You can use bullets intended for gas checks, just don't install the GC's. The smaller diameter base will help get the bullet/sabot down the barrel a little easier.
At least for me, the .452 bullet with the T/C sabot was really snug going down. That was good because I knew it would seal off the gases well and there is zero gas cutting on the sabot and no sabot residue in the barrel even after a session shooting 30+ shots. A loose sabot/bullet is not good in a muzzleloader. BTW, I never cleaned the bore of the gun during the 30+ shot session and there was no fouling of the barrel at all. A couple of patches soaked in Hoppes No.9 cleaned the bore followed by a couple of dry patches and one with a little oil before storage.