Final answer:
Guns that cannot be entered into the NCIC include toy guns, antiques not used in a crime, and firearms without a serial number unless they are involved in a crime. The NCIC is used by law enforcement to track firearms that are stolen, lost, or used in crimes.
Step-by-step explanation:
When referring to the types of guns that cannot be entered into the National Crime Information Center (NCIC), it's important to note that the NCIC is a federal database used by law enforcement agencies across the United States to track crime-related information. Guns that are generally not entered into the NCIC database include toy guns, antique firearms that are not used in a crime, and firearms that lack a serial number and cannot be uniquely identified, such as homemade firearms (sometimes referred to as "ghost guns") unless they are involved in a crime.
The NCIC system primarily includes records of stolen, lost, and recovered firearms, as well as those used in the commission of crimes. However, the inclusion of firearms into NCIC is governed by specific criteria, and the actual policies may change over time as laws are updated or revised.