The issue with hard cast bullets in the 45 auto is usually just diameter. I had one scruffy barrel that would lead a bit with hard bullets until I moved to the .4525-.4530" size range. They then obturate the bore by their diameter being great enough rather than by being upset by the pressure, as the softer, narrower bullets depend on being able to do. I've made both shoot just fine, and matching diameter is one key to it.
Where the soft bullet's "bumping up" from the pressure really outdoes hard cast bullets is in revolvers with smooth bore surfaces, but with a constriction where the barrel screws into the frame. In that situation the soft bullet can re-expand to keep the bore obturated (sealed off) after passing through the constriction, where a harder one cannot. Using a tighter spec, smooth surface 1911 barrel, on two occasions I have shot about 3000 rounds of commercial hard cast bullets through a 1911 over a three day period, without cleaning, and had no failures and no problems. At about the 3000 round mark, the powder and burned lube fouling had caked up enough in every nook and cranny that the gun started to fail to go fully into battery without some added thumb pressure being applied to the back end of the slide. No significant lead accumulation ever appeared. What little there was—traces between the lands back around the throat—seemed to be shooting itself out as fast as it was being picked up, as it just stayed at that level after the first fifty rounds or so.
I want to try the same endurance shooting with powder coated bullets and Hodgdon Universal sometime. Both are cleaner shooting than the lubricated cast bullets and Bullseye I was using on those two previous occasions.