Different specilizations of Beam Weapons default to each other at -2. Beam Weapons (pistol) defaults to Guns (pistol) at -2 and vice versa. Beam Weapons (rifle) defaults to Guns (rifle) at -2 and vice versa. Familiarity penalties still apply across these defaults - if you know Guns (pistol) and you pick up a laser pistol for the first time, you are at -2 for the default and -2 for familiarity.