TM 9-1275

(7) Barrel and receiver group. (a) The barrel is inspected visually to determine the condition of the bore and the deterioration that has taken place. A gage inspection is then made to determine the amount of wear that has taken place at the origin of the rifling with breech bore gage. (See fig. 6) The wear in the chamber or in the related parts affecting headspace is checked with the headspace gage specified in the serviceability chart. (See fig. 23)

(b) Gage inspection offers no problems, as the tolerances are definitely set; however, classification of barrels by visual inspection is a matter of individual skill and judgment and, therefore, offers many problems. Care in interpretation and application of the standards contained will aid in arriving at a uniform point of rejection. The point at which a barrel is rejected by visual inspection varies with the disposition to be made of the rifle immediately following inspection, as explained in b above.

1. Limits of serviceability for using organizations. The serviceability chart (fig. 23) shows the limits for breech bore (fig. 6) and headspace measurements. (See fig. 7) If the barrel is pitted to the extent that the sharpness of the lands is affected, or if it has a pit or pits in the lands or grooves large enough to permit the passage of gas past the bullet, it is to be scrapped. A pit, the width of a land or groove and 3/8 inch long or longer, indicated this condition. Examine barrel for mechanical damage and examine the chamber for deep pits that would seriously affect extraction.

2. Special requirements for oversea shipment. Breech bore (fig. 6) and headspace measurements (fig. 7) are to be within the limits set by the serviceability chart. (See fig. 23) Examine barrel for pits or mechanical damage. A barrel that is uniformly pitted but with sharp edges on the lands may be considered serviceable. Only those barrels which show excessive wear, developed pits, or which have pits cutting into the lands are unserviceable for oversea shipment.

3. Weapons placed in storage for reissue. Limits for breech bore (fig. 6) and headspace measurements are shown in the serviceability chart (See fig. 23) A few fine pits are acceptable. However, the general appearance of the bore should approximate that of a new barrel and should appear to have a minimum of 75 percent of its normal life left.

(c) The headspace of a rifle is measured as the distance between the shoulder of the chamber and the face of the bolt when the bolt is in a locked position. The minimum measurement is 1.940 inches. Headspace is important because it affects accuracy and safety. If the weapon has excess headspace when the round is fired, the thin portion of the case expands and grips the wall of the chamber, while the base of the case moves rearward to fill the room allowed by excessive headspace and pulls the case in two. This is called a ruptured cartridge case and allows gas to enter the receiver, often severely damaging the weapon. To obtain the headspace measurement, the headspace gauge is placed on the face of the bolt and so positioned that the ejector enters the clearance cut on the base of the headspace gage. If the bolt will close fully on a 1.940-inch gage and will not close on the maximum gage as specified by the serviceability chart (fig. 23) the headspace is satisfactory.

1. Certain gages of early manufacture do not have a bevel around the head of the gage. Do not use these gages on the rifle as interference will be encountered with the fillet around the face of the bolt and erroneous readings will be obtained. Certain other gages do not have the clearance cut for the ejector. When these gages are used, remove the ejector.

2. The most accurate method of taking headspace is with the operating rod removed, and the reading taken while rotating the bolt by hand. If it is found that the headspace of the rifle is over 1.950 inches, check the rifle with a field test bolt. (See fig 7) This will determine whether the excessive headspace is caused by a worn bolt or a worn barrel and receiver assembly. If the field test bolt will not close on a 1.950-inch headspace, the bolt is worn and must be replaced; if the field test bolt closes on the 1.950-inch gage, the barrel and receiver assembly is worn and must be replaced.

(d) With the action open, inspect the receiver for burs or other deformation.

(8) Bolt group. Test the bolt for freedom, smoothness of movement, and for locking. Insert bolt in receiver and function with fingers.

(9) Stock group. (a) Inspect the stock for cracks, scratches, bruises, or mutilations. Check for loose or bent sling swivels, burs, a loose front swivel screw, loose or burred stock ferrule, and for loose or missing butt plate screws. Check the seating of the butt plate, function of the butt plate cap, and the tension of the butt plate plunger spring. Make certain the combination tool, oiler, thong case, and rifle grease container are in the butt-well.

(b) Inspect the hand guards for cracks or scoring. Check the ferrule and rear hand guard band for looseness and burs. Check the lower band for looseness, burs, and loose or missing pin. The pin should be staked. Check the spacer in the front hand guard for position and looseness.

TM 9-1275