_The gauge finger should be between the index and ⅛ inch below the index._ It is the duty of the Chief Mechanic to see that the gauge finger is in the proper position before firing. It is the duty of the Executive and the Chief of Section to see that the gauge finger is in the proper position during fire; if it moves from this position the Chief Mechanic will be called to make the proper adjustments. When the gauge finger has been brought to the proper position there are only two conditions which call for tampering with recoil apparatus. 1. The gun goes into battery too slowly, or has to be pushed in. In this case the gauge finger will usually be found too deep in its seat, and the pump will have to be used. If the gauge is in the proper position look at the slides. Either they will be found dirty or bits of the wiper may be nicked off. In the latter case the gun can be fired without the wiper. 2. The gun jumps badly. In this case the gauge finger will generally be found beyond the index. When this is the case the oil extractor must be used until the gauge finger is in the proper position. If after cleaning slides, putting gun in abatage and adjusting gauge finger, the gun still jumps badly—complete draining of the reserve and refilling will frequently remedy the trouble. CHAPTER VII. 75-MM. FIELD GUN MODEL 1916. THE GUN. Weights and Dimensions. Weight Kg 339.74 pounds 749. Caliber mm 75. inches 2.953 Total length mm 2,308.5 inches 90.9 Length of bore mm 2,134. inches 84. Length of rifled portion of bore mm 1,847. inches 72.72 Number of grooves 24 Width of grooves mm 7.30 inches .2874 Depth of grooves mm .501 inches .02 Width of lands mm 2.52 inches .0992 Twist, right hand, zero turns from origin to a point 2.89 inches from origin. Increasing from one turn in 119 calibers at a point 2.89 inches from origin to one turn in 25.4 calibers at a point 9.72 inches from muzzle. Uniform from a point 9.72 inches from muzzle to the muzzle. Description of the 75-MM Field Gun. =The gun= is built up of alloy-steel forgings, _consisting of a tube, jacket, breech hoop, and clip_. All of the parts are assembled with a shrinkage. _The tube_ extends from the muzzle to the rear end of the powder chamber and two recesses are cut in its rear face to form seats for the lips on the extractors. _The jacket_ is assembled over the muzzle end of the tube. The jacket carries two flanges on its lower side, which form guides for the gun in the cradle of the carriage, and a lug on top near the forward end which contains a T slot, which holds the recoil cylinder in place. The rear end of the jacket is threaded on the outside to receive the breech hoop.