The Big Gun, Mountain summit in County Kerry, Ireland

The Big Gun is a 939-metre peak in the eastern MacGillycuddy's Reeks, set on a narrow rocky arête between Cnoc na Péiste to the southwest and Cruach Mhór to the north. Its summit is the ninth-highest in Ireland on the Arderin list and the tenth-highest on the Vandeleur-Lynam list.

The Big Gun is also recorded as Lackagarrin and Foilnabreachaun, with the Irish name An Gunna Mór. Its 939 m summit appears on the Arderin list as the ninth-highest peak in Ireland, and on the Vandeleur-Lynam list as the tenth-highest. The Scottish Mountaineering Club counts it among the 34 Furths, the 3,000 ft peaks outside Scotland, which is why it is sometimes called one of the 13 Irish Munros.

The peak's Irish name, An Gunna Mór, means "the big gun", and it also appears as Lackagarrin or Foilnabreachaun. The Scottish Mountaineering Club counts it among the 34 Furths, peaks over 3,000 ft outside Scotland, so it is sometimes called one of Ireland's 13 Munros.

The Big Gun is usually climbed as part of a horseshoe loop of the eastern Reeks, starting and ending at the Hag's Glen. The longer MacGillycuddy's Reeks Ridge Walk often begins at its eastern end, from Kate Kearney's Cottage in the Gap of Dunloe. The narrow rocky arête between Cnoc na Péiste and Cruach Mhór is exposed and serious, comparable to The Bones on the Beenkeragh Ridge.

The narrow rocky ridge connecting this summit to neighboring peaks creates a thin line of exposed rock that demands careful footwork and balance. This type of sharp formation appears rarely in Irish mountaineering and gives climbers an unusual experience on high ground.