Source: Arsenal, page 150
This modification replaces the metal components of a gun with ceramic/plasteel components to increase the difficulty of detecting the weapon via MAD systems. There are three levels of replacement: Level 1 provides a –2 dice pool modifier to detection tests, Level 2 provides a –4 dice pool modifier to detection tests, and Level 3 makes a weapon undetectable by MAD systems. Th is modification cannot be combined with the reduced weight mod (p. 153).
For the cost modifier you do not use the weapon’s basic cost, but its actual cost (basic cost + all previous modifications), because all those parts must be replaced in order for the modification to function properly. Likewise, when further modifying a weapon with the ceramic/plasteel components modification, apply the cost modifier to the material costs of the new modification and raise its Availability to that of the ceramic/plasteel modification, unless it is already higher.
For example, if a character wants to modify a Level 3 ceramic/plasteel rifle with a gas-vent 3 system (400¥, Availability 6R), he has to pay 2,400¥ (6 × 400) and the Availability for the material is not 6R but 20F.