From 3e Core revised, p51, on Guns:
“This is the ability to use any type of 20th-century cartridge-type gunpowder weapon. Add 1 to your skill for an IQ of 10 or 11, and 2 for an IQ of 12 or better. Modifiers: See Familiarity, p. 43. -2 for an unfamiliar weapon of a known type (e.g., .22-cal when...