Shooting my S&W 586 in 38spl (yep, not a typo) and after about 20 rounds heard an unmistakeable sound. Sounded like pulling your finger out of a bottle of coke or a small cork pop gun.
Went to open the cylinder to check the barrel and no dice. The bullet was lodged between the cylinder and the barrel at the forcing cone.
The range guy at Bass Pro grabbed a rod and tried to push it back but we couldn't get enough ooomph to get it to move. He was convinced it was a FTF and not a squib and wouldn't let me just pack it up and go. My wife was shooting next to me, breaking in her new SigP290. I had a Beretta Neos 22 with me so I shot that until my wife was done. When it was time to leave the RO had her take everything off the line and was going to have me walk out the door to the car carrying the fully loaded, but jammed, pistol out to the car. Luckily my range bag has detachable soft pockets so I placed it in one of those and proceeded to keep it pointed down on my way out. At least it was covered so no one would panic. The lady at the entrance gave me a raised eyebrow and I simply told her "it needs to go to a gunsmith and you don't really want to handle it", she got the picture.
Got home and, now with a proper vice and tools, tapped the bullet back into the case and opened the cylinder. I also had to tap the whole cartridge out of the cylinder since the HP had expanded a bit from the brass rod I used to ram it out.
I know exactly when I did it. I was using a new seating die and a few of my cases weren't expanded enough so the bullet bound up. I had removed the case, emptied the charge, used a Lee expander from their "classic" kit to open the mouth a little more and placed it back in the press without charging it. DOH!!!
No harm to anything other than my pride.

I've loaded several thousand rounds of all types and this is the first mistake I haven't caught.
