Ballistic tests were being carried out last night on an AK-47 rifle found by gardai during a planned search operation in Bray, Co Wicklow, yesterday.
The gun was found as officers used metal detectors and other search equipment to comb through undergrowth beside the exclusive St Gerard's School at Thornhill Road in Little Bray.
The tests will establish whether the gun is a replica or an authentic AK, which was the favoured weapon of the Provisional IRA during their terror campaign in Northern Ireland.
The find was made during searches that were planned in co-ordination with a series of raids on homes in the Bray area.
Gardai arrested five men, ranging in age from 26 to 46, and three women, aged 31, 29 and 26, in the swoop.
They were detained as part of an investigation into the shooting of Glen McGrath, who was gunned down outside the Cappagh Nua pub at Barry Road, Finglas, west Dublin, on December 30.
The suspects are being detained under section 30 of the Offences Against the State Act, which means they can be held without charge for up to three days.
Mr McGrath (40) had been talking on his mobile phone outside the pub when a black Volkswagen Golf 98-D registered estate car pulled up alongside him.
The gunman, who was in the front passenger seat, jumped out and fired six shots, hitting his victim three times in the chest.
Mr McGrath was taken by ambulance to James Connolly Memorial Hospital in Blanchardstown, Dublin, where his condition was initially described as critical. His condition later improved and he has since been discharged from hospital.
The getaway car was driven in the direction of Barry Avenue and was later located by gardai in the Charlestown area of Finglas.
After the discovery of the gun, gardai carried out further searches in the Bray area but nothing else was found. Officers said last night it was not yet clear if the weapon could be linked to the gang under investigation and they were awaiting the outcome of the forensic tests before making further inquiries.
They said the gun find and the arrests were not connected to a shooting incident in a Bray housing estate on Tuesday night and said the operation had been planned for some time.