Barrack buster is the colloquial name given to several improvised mortars, developed in the 1990s by the engineering group of the Provisional Irish Republican Army (IRA).
The first barrack buster - known to the British security forces as the Mark 15 mortar - consisted of a one metre long metal propane cylinder with a diameter of 36 cm that contained around 70 kg of home-made explosives and with a range between 75 and 275 m. The cylinder is an adaptation of a commercial 'Kosangas' gas cylinder for heating and cooking gas used in rural areas in Ireland.
It was first used in an attack on 7 December 1992 against a security base in Ballygawley, County Tyrone, in Northern Ireland, injuring a number of RUC officers. The projectile was deflected by the branches of a tree, which prevented further damage.
Read more about Barrack Buster: Provisional IRA's Improvised Mortars, Use By Other Groups, Colloquial Usage