1. n. [Perforating]

A perforating gun assembly designed to be used in a wellbore before the production tubulars or completion equipment have been installed, thus allowing access for a larger diameter gun assembly. Casing guns are typically 3- to 5-in in diameter and carry up to four perforating charges per foot.

See related terms: carrier gun,  perforating charge,  perforation density,  shaped charge