Having done this with a shotgun, dirt/mud in the end of the barrel, with a similar result, this one happened at the shooter end of the barrel. This tells me the barrel was blocked by a previous load or too much powder.
My guess is a previously loaded charge.
or used smokeless powder instead of BP or 777
My brother-in-law almost killed himself when the barrel of his was blocked by a previous load. It certainly screwed up the rifle....LOL!