The police can ask for the full name, address and age (and proof) of anyone who has, or recently had, a firearm (or is with someone who has), and can demand to see a firearm licence immediately or within 48 hours at a police station [Firearms Act 2015 (SA) ss 55 and 56]. Even people who may incriminate themselves have to provide proof or answer questions about the location of a firearm or identify anyone who has or has had possession of a firearm [s 55(7)].
The police can stop, detain and search any person or vehicle (and seize firearms, parts, and accessories) if they reasonably suspect that a firearm is unregistered or that a firearms offence is being committed or in other certain circumstances [Firearms Act 2015 (SA) s 57].
See further Common Offences, Weapons offences, Firearms.