Component of the cylindrical core that assembles on the inner surface of the capsid during capsid formation and plays a role in viral DNA ejection into the host cell. The inner core is composed of stacked rings of gp14, gp15 and gp16 proteins. Following binding to the host cell surface, the internal core is disassembled and gp14 is ejected along with gp15 and gp16 into the infected cell. May form a simple channel spanning the outer membrane. Interacts with the portal protein. Interacts with gp15. Belongs to the T7virus internal virion protein gp14 family.