If the recoil cylinder is not completely filled, loss of stability will occur and there is danger of serious damage to material. Before firing, a commissioned officer should always verify the filling of cylinder by removing one filling plug (with gun level) in which case oil should be visible above recoil valve. To fill recoil cylinder when assembled to carriage, elevate the gun about five degrees, remove both filling plugs and pour Hydroline oil in slowly with funnel until oil appears at rear filling plug hole. Level gun and again fill until oil appears at both filling holes. Shake carriage gently and continue to refill slowly until air ceases to come out of cylinder. Replace rear plug, elevate gun about five degrees, remove valve turn-gear cover, and loosen plug in end of piston rod sufficiently to allow oil to drip out. As soon as oil starts to drip, tighten plug; be sure that gasket is centered. Replace rear filling plug, rock carriage to permit air to escape from filling hole and fill with oil. Replace plug, level gun, and perform same operation with rear filling hole. When air is all out of cylinder, tighten both plugs and elevate to five degrees, allow to stand for about five minutes, then remove front plug and again refill. Loosen drain plug and drain out about ¼-gill of oil into receptacle. Do not allow oil to run down into gun slides. About four quarts of Hydroline oil is required to fill recoil cylinder. Oil must be clean and free from dirt and should be strained through clean linen or muslin cloth before using. In emergencies glycerin and water, or any buffer or engine oils may be used in recoil cylinders, but should be replaced by Hydroline as soon as possible. Where the above liquids are used, all interior parts of recoil mechanism must be emptied, disassembled, thoroughly cleaned and dried before refilling. CHAPTER VIII 75-MM FIELD GUN MODEL 1917 (BRITISH). Weights and Dimensions. Weight 995 lbs. Caliber 2.95 in. Total length 88.21 in. Length of bore 83.915 in. Length of rifled portion 72.72 in. Rifling 24 grooves, right hand twist, zero turns at the origin to 1 turn in 75 in. (25.4 calibers) at 9.72 in. from the muzzle thence uniform. The Carriage. Weight of carriage, complete 1950 lbs. Weight of gun and carriage complete 2945 lbs. Weight at end of trail carriage limbered 96 lbs. Diameter of wheels 56 in. Width of track 60 in. Length of recoil 49 in. Maximum angle of elevation 16 degrees Maximum angle of depression 5 degrees Maximum amount of traverse of gun on the carriage 142 mils DESCRIPTION.