Firearm malfunction
A firearm malfunction (also misfire and jam) is the partial or complete failure of a firearm to operate as intended. Malfunctions range from temporary and relatively safe situations, such as a casing that didn't eject, to potentially dangerous occurrences that may permanently damage the gun and cause injury or death. Malfunctions are sometimes considered a factor in negligent discharge. Proper cleaning and maintenance of a firearm play a big role in preventing malfunctions.
Cartridge malfunctions
Case head separation
Case head separation occurs when the walls of the casing become thin or fatigued. Upon firing the round, the case separates into two pieces near the head. It is not uncommon with brass that has been reloaded several times.
Dud
A dud (also a misfire or failure to fire) occurs when the trigger is pulled but the primer or powder in the cartridge malfunctions, causing the firearm not to discharge. Dud rounds can still be dangerous and should be deactivated and disposed of properly.