GENERAL DESCRIPTION.
Weight of the ·303-in. gun, 60 lbs. Weight of the tripod, 48 lbs. Weight of ammunition box containing one filled belt, Mark VI 21 lbs., Mark VII 19½ lbs.
The gun may be considered as divided into two portions—the non-recoiling and the recoiling. It is worked automatically by two forces—the explosion of the charge which forces the recoiling portion backwards, and a strong spring (called the fusee spring) which carries it forward.
Non-Recoiling Portion.
The non-recoiling portion consists of the barrel casing and breech casing, and is attached to the mounting by the crosshead and elevating joint pins.
The barrel casing is of gunmetal, holding about seven pints of water to keep the barrel cool when firing; it has three openings, one on the upper right side near the breech for filling, one underneath near the muzzle for drawing off the water, and the third (also near the muzzle) for allowing the steam, but not the water, to escape. The first two are closed with screwed plugs; the last is open and connected with the steam tube, and carries the condenser nipple.
A cork plug is provided which can be inserted in the steam escape hole when the gun is travelling, in order to prevent waste of water from jolting. The plug should always be taken out before commencing to fire, and put in again before the gun changes position, unless the condenser is attached to the barrel casing and can be conveniently moved with the gun.
To prevent the escape of water, there is at the forward end of the barrel casing asbestos packing, which is held in position round the barrel by the packing gland. At the rear end of the barrel there is a cannelure, also filled with asbestos packing, which prevents the escape of water when the gun is working, and a gunmetal valve immediately in front of the barrel block, which prevents the escape of water when the gun is not firing and the barrel home.
The steam tube consists of a fixed tube and an outer tube, termed the slide valve, so arranged as to slide freely along the fixed tube. In the fixed tube there is a hole near each end, and a third hole in the threaded portion in front, to connect with the steam escape hole which is bored in the solid part of the front end of the barrel casing. This tube is fixed into the solid end of the barrel casing, and is retained in position by a screw which, being kept in adjustment by a keeper screw, ensures that the third hole coincides with the steam escape hole. At the breech end it fits into a recess.
If the gun is fired with elevation, the valve slides backwards, and, closing up the hole at the rear end of the tube, prevents the water entering; at the same time it leaves the front hole uncovered, which, being above the water level, allows the steam to enter the tube and escape through the steam escape hole in the barrel casing. Similarly, if the gun is fired with depression, the valve slides forward and allows the steam, but not the water, to escape through the rear hole.