Refill and repeat two or three times. When satisfied that the cylinder is entirely full of oil, insert both plugs, and depress the gun to its maximum depression. After a few moments elevate again to its maximum elevation and unscrew both plugs. Now refill as described above. When entirely full, allow not more than two cubic inches (about one-fourth of a gill) of the oil to escape, insert both plugs and lash them with copper wire. It may happen that after firing a few rounds the gun will not return to battery. This may be due to, first, weakness of springs, second, stuffing box gland being screwed up too tight, or third, the oil having expanded, due to heat. It any case the cause must be ascertained and remedied, if due to expansion of oil, it is proven by the fact that the gun cannot be pushed into battery by force exerted on the breech of the gun. In that case elevate the gun to its maximum elevation and remove the filling plug. The oil will now escape permitting the gun to return to battery. In emergencies, water may be used in the cylinder. This should be done only when absolutely necessary, and never in freezing weather, and as soon as practicable the cylinder should be emptied, cleaned, and thoroughly dried and filled with hydroline oil. About 9 pints of hydroline oil are required for filling the recoil cylinder. =To empty the recoil cylinder.=—The cylinder may be emptied either when assembled or disassembled from the cradle. In either case, remove both the filling and drain plugs, depress the forward end of the cylinder and drain the contents into a clean can or other receptacle over which a piece of linen or muslin has been stretched, for straining the oil. =To clean the recoil cylinder oil.=—The hydroline oil used in the cylinder should be cleaned and free from grit and dirt. The oil should be stored in the closed cans provided for the purpose, and be carefully protected from dirt, sand, or water. Oil withdrawn from the cylinders and containing any sediment must not be used again until it has been allowed to settle for not less than 24 hours. When sediment has thus been permitted to settle great care must be taken not to disturb it in removing the oil. To insure the cleanliness of all cylinder oil it should be strained through a clean piece of linen or muslin before using.