Project eldest son was a covert operation conducted by United States Special Forces during the Vietnam War. The project focused on secretly planting self-destructive rounds in North Vietnamese weapon caches. The defective rounds would be identical to legitimate ammunition with one deadly difference, these rounds were designed to explode with enough to damage the weapon beyond repair and injure the shooter.
Green Berets would often brave Vietcong tunnels and the dangers within to compromise the integrity of enemy supplies. American technicians assembled 11,565 7.62×39mm cartridges for AK-47 rifles, 556 12.7×108mm heavy machine gun cartridges, and 1,968 82mm Type 67 mortar shells.
The goal of Project eldest son was to force communist forces to constantly question the validity and safety of the weapons they were using to kill American soldiers. The program also had some unintended benefits. Vietnamese troops started to lose faith in their Chinese suppliers and blame them for poor quality control.
The video below shows an example of what a Project Eldest Son style round can do to a weapon. The rifle being shot is a fully automatic MPI-KM 72. The gun is similar to the AK-47s used by communist forces and the two guns can be almost indistinguishable to the untrained eye.