Police from across the region, including the Dogs Operations Unit, conducted a search of a Mid North property, after receiving information from the public.
Police carried out the search just before 4.30pm on Sunday March 11, where they uncovered three modified firearms, one fitted with a silencer, a crossbow and another firearm alleged to be stored insecurely.
None of the modified firearms were registered and are suspected of having been stolen.
In the search, police also located a quantity of ammunition along with 35 grams of cannabis and drug paraphernalia.
A 65-year-old man from Two Wells was reported for insecure firearms and a 67-year-old man from Gawler West was reported for possessing a prohibited weapon.
A 37-year-old man and a 35-year-old woman from the Mid North were arrested and have been charged with a raft of firearm offences, unlawful possession and possessing cannabis.
Both the 65 and 67 year-old-men will appear in the Port Pirie Magistrates Court at a later date.
The woman was bailed to appear in the Port Pirie Magistrates Court on April 16, while the man was refused bail and appeared on Tuesday March 13.