Trunnion Hole
Trunnion hole a of the gun carriage, consists of a circular indentation in each carriage cheek, in which the trunnions of the gun barrel will rest, and which must be placed in such a way that limbering is made easier without also making the carriage too front weighted, in which case the trail would lift off the ground every time the gun is fired. S. Gun Carriage.
Source: Rumpf, H. F.: Allgemeine Real-Encyclopädie der gesammten Kriegskunst (Berl. 1827)