30,000 is the maximum voltage that could jump across stun gun contacts spaced one centimeter apart. Any claimed voltage greater violates the laws of physics. Here's why.
Maximum electric field (Emax) refers to the potential electric energy that can occupy a physical space. "The magnitude of the electric field for which dielectric breakdown occurs in a material is called the dielectric strength of that material," explains Physics for Scientists and Engineers: Regular Version. "The dielectric breakdown [when nonconducting materials become ionized in very high electric fields and become conductors] occurs in air at an electric field strength of Emax = 3 x 106 volts (V) per meter (m).
In other words, we can calculate the maximum voltage a conductor - in this case, air, as in the space between the stun gun contacts - can maintain using the equation Emax = 3 x 106 volts (V) per meter (m).
So, let's calculate the dielectric breakdown of air when contacts are spaced 0.01 m (1 cm) apart.
Emax = 3 x 106 V per 0.01 m
Emax = 3 x 1,000,000 V per 0.01 m
Emax = 3,000,000 V per 0.01 m
Emax = 3,000,000 V x 0.01
Emax = 30,000 V
When stun gun contacts are placed 1 cm apart, voltage cannot exceed 30,000 V.