It is a nylon dummy round which simulates the Type 3 Malfunction, exactly as we would experience it in reality, under live fire training conditions.
The Type3MalfunctionRound™ is made of a proprietary nylon resin which is designed to protect the internal steel parts of the firearm from being damaged. The Type3MalfunctionRound™ takes the beating instead of the gun. The Type3MalfunctionRound™ will give the user as many as 500 type 3 malfunction training opportunities, before needing to be replaced.
Even though double feeds don't happen often, it is still very wise to practice them. You don't want the first time you deal with a type 3 to be during a defensive lethal force encounter protecting yourself or your family.
A defensive pistol shooter should be able to clear a type 3 malfunction as easily as they can perform an emergency reload. The type 3 and bolt lock are very similar! They both have a dead trigger, and they both lock the bolt open. But they require different steps. And they are both critical to train.