Originally Posted by VABAM

That looks like a casing blow out due to bad/old brass. Happened to me once when using reloaded ammo my dad had bought at a gun show. Luckily the gun was a Berretta 92FS and I was wearing eye pro, had burning powder and brass fragments hit my face. A couple of parts popped out but I was able to put the gun back together at the range. Then my dad took a turn and not even a mag later it happened again. Some people might bad mouth the 92FS but it is a tough gun. Even after having 2 case blow outs in one outing it was functional after a little bit of help. We took a closer look at the batch of ammo and found a few rounds were the casing was visibly cracked. The lesson here is to be careful when purchasing reloaded ammo, especially semi-auto pistol ammo.