Double yikes. This shooter is lucky to be alive. Here’s the story: an inexperienced Smith and Wesson M&P owner decided that his .40S&W chambered handgun could also shoot 9mm – without switching barrels. What happens next is cringeworthy; he proceeds to load up a magazine, alternating between the two different caliber rounds.
The first shot, a .40S&W, functions normally, but the second round, a 9mm, is where everything falls off the rails. Whether or not the round actually fires and the spent case follows it into the barrel or the entire unfired round is pushed into the barrel is unclear. Either way, at this point the barrel is obstructed.
The next (and final) shot is a .40S&W that chambers and fires as designed. The bullet strikes the 9mm case in the barrel, causing the resulting damage seen here. Luckily, no one was injured.
I go back and forth in thinking whether or not the 9mm round actually fired. On the one hand, the damage makes me think that the .40S&W impacted the primer and caused a secondary explosion inside the barrel. On the other hand, a 9mm case, when fired in a larger diameter barrel, has been known to expand to fit inside the barrel. That bloated casing halfway into the barrel could cause a blockage bad enough to expand a bullet on impact.
Though the shooter is unwilling to discuss the incident, I did have the chance to chat briefly with a friend of his who was at the the range that day. He says that his friend, though unharmed, is too embarrassed to discuss the mishap.
Be careful, be observant and ask questions when something doesn’t feel right. And carry a medical ‘blowout kit’ at everybody range session.
Not to add insult to injury, but M&P conversion barrels can be found at online retailers like Brownells.