Gardai carried out a search of a wooded area in Shannon on Friday afternoon.
A man remains in custody this morning after a gun was found in County Clare.
Ammunition was also recovered during a search.
Gardai carried out a search of a wooded area in Shannon on Friday afternoon.
They were helped by the Emergency Response Unit and Southern Region Dog Unit.
They discovered a Colt M16 rifle, magazine and over 170 rounds of ammunition.
A man in his 30s has been arrested and remains in custody this morning at a Garda station in County Clare.
He can be held for up to 3 days.
The gun and ammunition will be analysed by the Ballistics Section of the Garda National Technical Bureau.