Muzzleloading rifles (also known as “muzzleloaders”) can be safe and enjoyable firearms for shooting and hunting if handled properly. There are a number of muzzleloader constructs such as inline, flint lock and percussion. These firearms operate on the ignition of black powder propellant or approved substitute charge. There are a number of mechanisms that can be utilized to ignite the powder (e.g. primers, percussion caps, etc.); once the powder is ignited, the pressure builds up rapidly and then decreases as the projectile moves down the barrel and the volume of the gas behind the projectile increases. If circumstances arise that impede the motion of the projectile, such as an obstruction, then a marked over-pressurization event may occur causing ductile fracture of the barrel. Often, the location of the fracture(s) and the deformation of the barrel provide clues as to the type of obstruction. In this study, we investigate several examples of obstructions causing over-pressurization events that led to ductile fracture of the barrels.