After rereading this entire thread, I was reminded of something General Hatcher talked about with reference to accidents involving low numbered Springfields.
One of the problems had to do with the issue ammunition used at the time, so called "tin can" ammunition, which used bullets with silver colored jackets. These jackets were notorious for leaving metal fouling in the barrels, so the shooters took to lubricating them with a Mobil Oil product which they carried with them to the firing line and dipped the bullets in before loading them in the magazine.
The problem was that the lubricant, if not carefully applied, tended to migrate to the necks of the cartridge cases and thence to the rifle chamber. Oil and grease are incompressible substances, and the result of having one of them in the neck of the chamber was the same as firing a cartridge with a neck thickness so great that the neck was unable to expand and release the bullet.
Is it possible that some of the lubricant from your cast bullets might have ended up in the chamber and caused the same event to occur?
I am not familiar with tumble lubricating cast bullets, so I have no way of estimating whether of not this could have occurred. All my cast bullets have been lubricated with a device which lubricates and sizes simultaneously, so this is not a possibility with them.
