The man was detained during an operation in which a firearm was recovered at the rear of a flat, at Main St, Bruff, Co Limerick, around 34km from Limerick City.
The gun was discovered in wrapping, however gardaí said they were satisfied it was a firearm.
The weapon was taken to Limerick City where it will be transported onto Garda headquarters in Dublin for forensic testing.
Plainclothes detectives and local uniformed gardaí were backed up by an armed support unit.
The officers did not draw their weapons but carried out searches of the flat’s interior and a rear garden. Gardaí maintained a presence in the normally quiet town for most of the day.
A second well-known crime family from Limerick City who moved to Bruff several months ago are also being investigated.