He's very fortunate that he didn't get hurt or hurt someone else. Reloading is a great hobby by itself, but requires 110% focus. Check and recheck loading data before you start, and NEVER use data from an internet source, no matter who it is.

I was shooting at an indoor range next to a very friendly older gentleman with a S&W .38 Spl revolver. He was shooting wadcutters using a very light load of Bullseye, and shooting very well from years of practice. The last shot of his string took the top half of the cylinder off and bent the topstrap backwards into a "C" shape. Amazingly, no one was hurt despite a crowded range and all the metal that was flying around. The poor guy was very apologetic and embarassed. He had been reloading for 50 years, and never before had an incident. Looking down into cases in a loading block, it is impossible to tell if a case has been overcharged using 2 or 3 grains of a fast burning powder like Bullseye. They all look the same, but he had mistakenly double charged one of them. An easy mistake to make, that could have been his last.

Focus, focus, focus!