Gardaí seized a submachine gun during a raid in the Balgaddy area of Lucan on Sunday evening.
The deadly weapon - which has a rate of fire of 650 rounds per minute - was loaded and another clip of ammunition was also recovered.
It is believed the weapon, a PM 63 RAK, was intended for use by members of a gang in a Clondalkin feud.
According to Dublin Live, a source said:
“There are a number of active feuds in Dublin – this is probably one of the top most deadly feuds.
"This gun was intended for a murder and it was about to be carried out in the coming days. Gardai, acting on intelligence, moved in and took it out of circulation.”
A garda spokesman said: “As part of ongoing investigations targeting serious criminal activity in the Dublin Region being conducted by the Garda National Drugs & Organised Crime Bureau supported by the Special Crime Task Force, a targeted search operation occurred in the Balgaddy area of Lucan, Co. Dublin on the evening of the 21st January 2018.
“During this search operation a loaded "PM – 63 RAK” sub machine gun (pending ballistic examination) with an additional clip of ammunition was recovered. One male aged 20 year has been arrested and is currently detained at Ronanstown Garda Station under the provisions of Section 30 of the Offences Against the State Act 1939 as amended.”
A man arrested in the raid is currently being detained for questioning.