TM 9-1275

a. Correcting Angle on Follower. If angle on follower is not within the required limits (fig. 36), bend slides to correct angle by lightly tapping with a brass hammer.
b. Operating Rod. (1) The operating rod tube (fig. 24) is slightly offset to provide clearance at the enlarged portion of the barrel. This offset is not to be changed. When the operating rod is assembled to the rifle by the manufacturer, the operating rod is fitted to its respective rifle by bending.

Note. This is an operation requiring considerable training and is not practiced by field organizations. For this reason operating rods should not be exchanges among rifles if it can be avoided.

(2) Remove all rust and accumulated carbon from the tube with a fine abrasive and rifle bore cleaner.

Caution: Exercise extreme care to prevent rounding the edges or reducing the diameter of the piston. Do not use emery or other abrasives on this component because no shine or polish is necessary on the piston.

c. Gas Cylinder. (1) To remove accumulated deposits of carbon from the gas cylinder, remove the lock screw and remove the carbon with the screw driver blade of the combination tool or a similar instrument. The gas cylinder lock may be removed and the screw reinserted in the gas cylinder and threaded in far enough to break loose the carbon. Exercise care not to cross the threads. The gas cylinder port can be cleaned with a straight punch or the drift on the combinations tool. The inside of the gas cylinder is to be thoroughly wiped clean and oiled. A few drops of oil placed between the rear gas cylinder lug and the operating rod, with the muzzle tipped down, will be sufficient. Hand operate the rod through a few cycles to distribute the oil properly. Remove any rust on the outside of the cylinder, using rifle bore cleaner or fine abrasive. Remove rust on the barrel at this point in a similar manner.
(2) If the bayonet lug is worn to a loose fit with the ways in the bayonet, the lug may be peened lightly to provide a better fit. Rest the lug on a solid surface when peening.
d. Gas Cylinder Lock. (1) Excessive thickness. Difficulty may be experienced in fitting the bayonet to the rifle due to excessive thickness or lack of concentricity of the gas cylinder lock. (See fig. 38) This is rectified by grinding or filing the portion of the gas cylinder lock that fits inside the bayonet guard.
(2) Installation. Position the cylinder on the barrel. (See fig. 38) Screw gas cylinder lock down as far as possible by hand. Do not force. Unscrew the lock until the screw hole in the lock lines up with the threaded hole in the gas cylinder, permitting assembly of the gas cylinder lock screw. In some cases the lock will have to be unscrewed almost a full turn. Turn screw in several threads with fingers only. Push the gas cylinder lightly toward the muzzle until it rests against the lock and tighten screw.
e. Rear Sight Assembly. (1) General. The rear sight assembly of present manufacture (fig. 46) offers no unusual maintenance problems, but differs from sights of early manufacture (fig. 45) in that the elevating pinion and windage knob have been replaced by assemblies. The elevating knob assembly replaces the elevating pinion, elevating knob, and elevating screw. This assembly cannot be disassembled and no attempt is made to disassemble it. If refinishing is required, it is to be refinished as a unit. The windage knob assembly will be handled in the same manner. This assembly replaces the windage knob, the rear sight nut, rear sight nut lock, and rear sight nut lock spring. The new assembly is designed to overcome the requirement for loosening and retightening the rear sight nut between sight settings. In the case of this sight, the pinion is not to be staked after assembly.
(2) Staking rear sight pinion - early manufacture. When assembly and final adjustments of the rear sight of early manufacture are completed, lightly stake the rear sight pinion as shown in figure 47, to prevent the nut from becoming lost in service. An automatic punch, if available, can be used to better advantage than rear sight pinion punch when performing this operation.

Note. Place a lead bar or piece of hard wood under the elevating knob before staking, so as not to damage rear sight assembly.

f. Barrel. (1) Rust on barrel. Remove rust from the side of the barrel by rubbing with a cloth and wiping with preservative lubricating oil (special). If this is not sufficient, use a crocus cloth lightly, taking care not to produce a shiny surface. Make certain that there is no rust or foreign matter in the gas port and where the gas cylinder contacts barrel. The outside diameter of the barrel at bearing for gas cylinders must not be reduced, since any leakage of gas between the barrel and gas cylinder greatly reduces the power available to operate the weapon and, therefore, promotes short recoil stoppages. Check diameter after cleaning with barrel diameter at gas port gage. (See fig. 48)
(2) Carbon in the gas port. The gas port in the rifle barrels is not to be enlarged. It is permissible to remove carbon, corrosion, or fouling, which may have accumulated, by passing a 0.0805-inch drill through the port.

Note. It is not to be drilled larger than 0.0805 inch.

If the port is increased in diameter to make one rifle function, and the gas cylinder is replaced at a later date by a cylinder manufactured to the extremes of drawing tolerance, which tends to increase the power of the rifle, a malfunction may occur. The bolt speed will increase, increasing the force with which the bolt strikes the rear of the receiver. The bolt then bounces off the receiver with such speed that the ammunition may not have had time to reach the feeding position, and a feed stoppage occurs. Occasionally the added velocity of the bolt is sufficient to break the receiver, which would be a definite hazard to the firer.
g. Telescope Mount And Bracket (U.S. Rifle, Cal. .30., M1C (Sniper's) Only). A fine-grained, three cornered sharpening stone or fine, three-cornered file may be used to remove burs from the male and female dovetail slides. Replace screws which are stripped or worn to a loose fit.

TM 9-1275