Jeffrey Bangu was charged with drug offences in connection with the operation.
Jeffrey Bangu, 19, with an address at Cardy Rock Crescent, Balbriggan, was charged with drug offences in connection with the operation.
He was refused bail after appearing at Dublin District Court on Saturday.
Garda Eoin O’Reilly charged him with possessing cocaine and cannabis for sale or supply at his home on August 31, contrary to the Misuse of Drugs Act.
He has not yet indicated a plea and "made no reply" when gardai charged him following his arrest on Friday afternoon.
Objecting to bail, Garda O’Reilly told Judge Marie Quirke the local drugs unit obtained a warrant to search the accused's residence.
The court heard that during the operation, gardai found an "improvised slam-bang" shotgun in a bag with six 12-gauge cartridges on the floor. He said the homemade gun was "capable of causing serious harm or death".
Under cross-examination, he conceded the designated firearms officer was not at the hearing.
It was alleged they also recovered about €1,800 worth of cocaine and cannabis valued at €2,100 in the room.
The garda added that the seizure of Mr Bangu's wallet there supported the belief it was his bedroom.
The court heard gardai found a further €1,400 worth of cocaine and €2,100 of cannabis in another room and an imitation gun described as an air pistol underneath a bathtub.
The contested bail hearing was also told that there was paraphernalia, including bags and weighing scales.
The Director of Public Prosecutions (DPP) has yet to decide if the case will remain in the District Court or go forward to the Circuit Court, which has wider sentencing powers.
Defence solicitor Michael Byrne argued that there was no evidence the items were in his client's bedroom.
He submitted that the teenager would abide by a range of conditions, including a nightly curfew, providing gardai with his mobile phone number and being contactable at all times.
Pleading for bail, the solicitor described the allegations as vague.
Judge Quirke stressed that Mr Bangu had the presumption of innocence; however, noting the garda evidence, she refused bail.
Mr Bangu was remanded in custody to appear at Cloverhill District Court on Friday pending directions from the DPP.
Legal aid was granted to the part-time worker, who provided a statement of his means, but remained silent during the hearing.