What I want to know is why the tail guns of a Lanc only have 670 rounds? My sources indicate that the true load for this turret was actually 2500 rounds per gun. So the turret as a whole should have 10,000 rounds fired 4 at a time.
The Lanc's tail turret was fed by long feed tracks running up the fuselage all the way past the mid-upper turret to footlocker-sized boxes mounted above the rear end of the bombbay. The tracks alone held 600 rounds per gun, and the boxes another 1900 per gun.