If guns fails to return to battery after a few rounds of rapid firing, it is probably due to expansion of oil. This may be determined and corrected by loosening filling plug. If oil spurts out, allow it to run until gun is back in battery. It may be necessary to relieve oil two or three times immediately after filling. Gun should never be allowed to remain out of battery more than 1 inch on counter recoil without determining and correcting the cause. If gun remains out of battery and the relief of oil does not cause it to return, it is due to: (a) Weak or broken springs; (b) piston-rod gland too tight; (c) dirt or lack of lubrication in gun slides; (d) distortion of gun on gun ways; (e) distortion of piston rod due to improper counter recoil action. The majority of cases are due to (a), (b) and (c). (a) Can be determined only by removing springs, and should be undertaken only after all other methods have been tried. (b) Can be determined by loosening piston-rod gland. If gland is too tight, gun will return to battery when it is loosened. If gland cannot be loosened, piston-rod is probably distorted. (c) Flood slides with oil, and if possible retract gun and examine gun ways and slide for dirt. (d) If possible allow gun to cool for 15 or 20 minutes. In case of (a), (c) or (d) gun can generally be pushed back into battery by hand. (e) If piston rod or interior mechanism is distorted, mechanism must be disassembled and defective parts replaced. If distortion has occurred, it can generally be identified by very rapid counter recoil for round on which gun does not return to battery. This may be caused by foreign matter in oil causing buffer valve to stick, or by lack of sufficient oil. If distortion has occurred, it will be near gland and can generally be felt by running hand along rod from bracket to gland. [Illustration: 75 MM. GUN CARRIAGE MODEL OF 1916 VALVE TURNING GEAR AND RECOIL CYLINDER ASSEMBLED.] In case of any improper functioning of recoil mechanism during recoil or counter recoil, cease firing until cause has been determined and corrected. A piece is out of action when recoil mechanism is not operating properly and will almost certainly be damaged seriously if further firing is attempted. After dismounting any part of recoil mechanism or filling recoil cylinder, gun is to be retracted and released to allow counter recoil if possible. In performing this test, valve-turning mechanism must be disconnected and valve turned to correspond to an elevation of carriage of 53° before gun is retracted. Gun must not be held out of battery more than 10 seconds before being released.