That depends on a number of things. The most common things you need to know are emplacement status and how it fires will affect the answer. An unemplaced gun loses concealment automatically on LOS. A HIP gun will be placed on board concealed on LOS. If the gun fires using IFE or is a RCL, or if it rolls its colored dr high enough it loses concealment when it attacks per concealment table case G (or if it changes CA). See the concealment table for more details.