In the thread “Revolver Question” gpidaho asked if .001” clearance between the loaded round and the neck area of the chamber in a revolver was enough to provide enough expansion for safety when using cast bullets. This is a reasonable worry given the conventional gun lore about the danger of the neck of a case restrained by the chamber holding on to the bullet and causing a pressure spike. I can believe that in some extreme cases as when the jacketed bullet is bound to the neck by dried sealer or some kind of chemical bond, the force required to break that bond might cause higher pressure. It seems like Hatcher had something to say about this but my copy of his Notebook is packed for shipment and I'm not sure in which box.
However, I have often wondered if there is any real danger of this happening with a cast bullet and it seems doubtful to me. Even if the neck of the cartridge had no room for expansion at all the slick lead bullet shouldn't have any more resistance to being pushed out of the case by the expanding gas than it took to push in in (seat the bullet.) This force needed to push or pull the bullet out of the neck is tiny compared to the force needed to accelerate the bullet to muzzle velocity (perhaps 50 pounds vs. several thousand pounds) and given the variation in chamber pressure, the force needed to overcome friction between the case neck and bullet must be in the round off error. Do we have any evidence to the contrary? By this I mean pressure test data not just some expert's opinion about what might have blown up a gun after the fact. If someone equipped to measure chamber pressure has observed a pressure spike when there is no clearance between the neck of the cartridge with a cast bullet and chamber that would be convincing. Does anybody know of such a test producing such a result? Unless there have been such tests maybe we should question this bit of conventional wisdom.