One needs only to work in the Firearms industry for a short period of time before seeing one of these come across the gunsmith’s bench: a blown out or bulged barrel. Yes, it happens that often.
The question is why? Barrels are made from good quality steel, and they are tested prior to leaving the manufacturer. In Europe they use a proof house that tests the barrels to a 20% over loaded round. So, how can this still happen?
People tend to forget that when firing a gun you are holding a controlled explosion in your hand. If something goes wrong, that explosion is no longer controlled. The biggest reason this occurs is due to a bore blockage. A bore blockage can occur if you put the muzzle of the firearm in the dirt or mud, if you fire a round that does not leave the barrel or one that slows in the barrel.
This creates a back pressure of burning powder in the barrel. The pressures are rather intense and have to go somewhere. If the primary directions for pressures to go are blocked, then it is going force the barrel to flex. Some times, that pressure stretches the metal, and in some cases it forces the metal to the breaking point. This is not a defect in the metal – it’s the physics of the explosion of gasses in a contained tube.
I hear quite often ” I was using factory ammunition. This shouldn’t happen” I don’t disagree, however production ammunition is just that: production. The ammunition is produced and inspected by humans; errors can occur. With shotguns, sometimes the wad gets stuck on a loose choke tube, or the wrong choke tube used with steel shot. This happens a lot during duck and goose hunting seasons.
With reloaded ammunition, it could be as simple as a powder charge that didn’t go in, or a weak primer that didn’t ignite the powder. In any case, as a gun owner, you should be aware of what is going on with your firearm. If the shot doesn’t sound right, check the gun. If it goes pop instead of bang, check it. Normally, if you keep your firearm clean and lubricated and use good quality ammunition, this will not likely occur.
If you experience a bulged or exploded barrel, render the firearm safe and take it to your local gunsmith. He will tell you if it can be repaired.