There are many types of ammunition used in the military. What the rest of the world would call a full metal jacket, or a jacketed bullet, one that has a thin coating of a semi-soft metal such as copper over the lead, the military calls "Ball" ammunition. Put a thin coating of a phospherous type chemical over the metal coating and it will burn when fired becoming a "Tracer". Some ammunition has a super-hard, super-sharp pointed bullet that is designed to cut through metal, thus becomes "Armor-Piercing". Some ammunition has a small amount of explosive in the tip and becomes "Incendiary". One particularly fun piece of military ammunition is fired through a .50 caliber machine gun and combines a few of the above mentioned features to become an "Armor-Piercing, Incendiary, Tracer" or APIT. When APIT rounds hit their target they look like a bunch of little explosions...like on Airwolf. Some ammunition is designed for training, no propellant or explosives or any other features, just an empty brass casing and inert bullet. These are called "Dummy" ammo.

When the bullet is removed from a regular cartridge and the brass plugged or crimped, it can be used to simulate bullet firing, as in ceremonies and burials, and is called a "Blank" (Caution: blanks still have gun powder in them and when they are fired the escaping gases can be deadly up to a few feet away. Google "John Eric Hexum" for proof). When ammunition works as it is intended, none of our side has to suffer for it. But sometimes a bullet (we are talking about BIG bullets now, artillery-type bullets) will fly straight and true and hit its mark but not explode as it should. It lies there, still fully capable of exploding, but for some unfathonable reason has decided not to explode at this time. These are called "Duds" or "Unexploded Ordinance". They are dangerous because they may explode at any time, they have the potential to be deadly.

I learned all this a long time ago at the feet of a seasoned veteran of WWII and Korea. He heard my squad leader call me a "Dud" because of some infraction, I don't even remember what. Old Sergeant First Class Thatcher stopped my squad leader, Pinkelton, and told him not to call me a dud. He explained why. He pointed out that a dud is an unexploded round that has the potential to explode. This private (meaning me) does not meet that criteria, he has no potential...therefore, he is a dummy.