Slug the throat of the bbl. and if you don't cast, order your bullets to throat Dia. or .001 larger.
Imange a marble droped into a funnel that's at a 45* angle, the marble will rattle around as it travels to the bottom of the funnel. That's the same thing a bullet does that's smaller than the throat.
Next, see if you can touch the lands with a seated bullet. Drop a cast bullet into the chamber, then insert a sized & belled case, now try to close the action and see if the bullet has gone into the case. If so, this would be your optiomal seating depth, where the bullet is centered in the throat and touching the lands. If not, go with a bullet .001 over throat Dia.
You might go to the LBT's forum and sak if he knows of anyone selling his WFN design in.45 [.453], next would be Ranch Dog's design's.
You might someone to sell you a few heavy 45's over on the "Cast Boolet" forum/