2 vises, a handful of bullets, with a steel plate clamped to the end of the barrel. Then use a hydraulic press to smash the bullets in the barrel. Was this what happened, I don't know, but it is as good of an excuse as any.
I would think they would evenly compress the bullets and not bulge the barrel using the press. They would also have to have a dowel in the end to take up the space where there are no bullets at the muzzle end, and somehow not pancake the front edge of the bullet in the process.
Looks like a bunch of rounds with no powder charge, and a shooter that assume he was missing all the time. One good round along the way would have been a very sad deal indeed.