TM 9-1275, MALFUNCTIONS & CORRECTIONS

Section 10. Paragraphs 40-51

MALFUNCTIONS AND CORRECTIONS

40. Scope

The malfunctions and corrections contained herein are supplementary to those contained in using arm manual FM 23-5. Although the same malfunction may appear in both the using arm manual and in this manual, the possible causes and corrective actions contained herein are in addition to those covered in the using arm manual. Therefore, when malfunctions are being corrected by ordnance personnel reference to FM 23-5 will be necessary.

41. Clip Inserts with Difficulty

If difficulty is encountered in inserting a loaded clip in the receiver of a rifle which has previously been loaded without apparent difficulty, it may be assumed to be caused by a deformed clip which should be discarded. However, if continued trouble is encountered in inserting loaded clips, it may be caused by one or more of the following reasons:

a. POINT OF CLIP EJECTOR TOO LONG

If the offset point of the clip ejector is too long, it may scrape against the side of the magazine aperture in the stock, thereby making it difficult to depress the clip ejector. Disassemble the barrel and receiver group and trigger housing group from the stock, then reassemble the two groups together without the stock. Note the position of the offset point of the clip ejector in regard to the outside face of the magazine of the receiver. If it protrudes beyond this face, the point of the clip ejector is too long. Remove the clip ejector from the trigger housing group in accordance with FM 23-5 and grind the offset point until sufficient clearance is obtained.

b. BURRS IN MAGAZINES.

With the trigger housing group removed from the receiver and the bolt retracted, examine the magazine for burrs. Burrs in the follower and slideways will prevent the follower and slide from functioning, thereby making it difficult to insert a loaded clip. Remove burrs with a fine-grained sharpening stone.

c. INTERFERENCE BETWEEN BULLET GUIDE AND FOLLOWER ARM.

Remove the barrel and receiver group from the stock and retract the bolt. With the right hand holding against the operating handle so that the bolt does not release, depress the follower and slide several times with the left hand and observe if interference is encountered between the bullet guide and follower arm. This interference is often caused by the opening in the bullet guide being "squeezed in" thereby causing the follower arm or follower rod to drag on the bullet guide. Remove the bullet guide from the receiver in accordance with FM 23-5 and with a suitable wedge spread the opening until suitable clearance is obtained between the bullet guide and follower arm.

42. Short Recoil

Short recoil stoppages, often confused with feed stoppages, occur in rifles which are underpowered; and therefore do not drive the operating rod completely to the rear. When a weapon is underpowered, and thus subject to short recoil stoppages, it will usually close on an empty chamber or fail to eject the fired case, closing with the spent case in the chamber. This is the type of malfunction which occurs most frequently in the rifles. In analyzing this type of stoppage, the possible causes listed below should be carefully checked:

a. UNDERSIZED PISTON. Refer to paragraph 20d.

b. OVERSIZED GAS CYLINDER. Refer to paragraph 20g.

c. UNDERSIZED BARREL AT SPLINED SECTION. Refer to paragraph 21f.

d. CARBON OR FOREIGN MATTER IN GAS PORT OF BARREL. Refer to paragraph 21f.

e. CARBON IN GAS CYLINDER. Refer to paragraph 21c.

f. OPERATING ROD BINDING. Refer to paragraphs 20d and 30,

g. VALVE LEAK IN GAS CYLINDER LOCK SCREW. Refer to paragraph 20g.

h. DEFECTIVE OPERATING ROD SPRING. Refer to paragraph 20c.

i. BOLT BINDING. With the follower rod and operating rod removed from the rifle, operate the bolt back and forth several times by hand and note where it is binding. The rear lug on the bolt dragging on the receiver and heavy or burred locking lugs are the two most common causes of a binding bolt. Remove the bolt from the receiver in accordance with FM 23-5 and with a fine, flat file or fine-grained sharpening stone remove just enough metal so that when the rifle is tipped up and down, the operating rod and bolt, with the follower rod and operating rod spring removed, will move from closed to open position and back by their own weight.

j. BURRS, FOREIGN MATTER AND IMPROPER LUBRICATION. Refer to Section 4.

k. RUSTY OR RINGED CHAMBER. Clean the rifle barrel in accordance with instructions contained in FM 23-5 and examine it as outlined in paragraph 9c of this manual. If barrel is unserviceable, refer to paragraph 22c for instructions on replacement.

43. Bolt Fails to Close Tightly After Fire.

This condition may be due to one or more of the following causes:

a. EXTRACTOR DOES NOT OPEN ENOUGH TO PASS OVER RIM OF CARTRIDGE. The most common cause of the extractor failing to open sufficiently to pass over the rim of the cartridge is chips or foreign matter lodged between the heel of the extractor and the locking lug on the bolt which houses the extractor spring plunger. Remove the extractor, extractor spring plunger assembly, and the cartridge ejector assembly in accordance with paragraph 19e. Clean all parts thoroughly. Check the extractor and extractor spring plunger for free action in their apertures in the bolt, as binding of these parts will prevent the extractor from opening.

b. OPERATING ROD BINDING. Refer to paragraphs 20d and 30.

c. WEAK OR BROKEN OPERATING ROD SPRING. Refer to paragraph 20c.

d. ROUGH OR DIRTY CHAMBER. Refer to paragraph 42 above.

e. INSUFFICIENT HEADSPACE. Refer to paragraphs 9c and 22d.

44. Failure to Feed.

Feed failures, as in the case of short recoil stoppages, may cause the weapon to close on an empty chamber. This may be caused by excessive bolt speed when the bolt moves so rapidly on the forward stroke that the ammunition does not have time to obtain its proper feeding position. This condition is often caused by unauthorized modification of the weapon, such as increasing the gas port diameter. (See par. 21f). It also may be caused by any of the following reasons:

a. INSUFFICIENT REARWARD TRAVEL FOR BOLT TO PICK UP NEXT ROUND DUE TO INSUFFICIENT RECOIL. Refer to paragraph 42 above.

b. LONG EJECTOR. If the ejector is too long and protrudes beyond the rim on the front of the bolt, the cartridge will be prevented from rising to its proper position in front of the bolt. Remove the ejector from the bolt in accordance with paragraph 19e and grind or file sufficient metal from the ejector so that it lies below the rim on the front of the bolt.

c. WORN OR IMPROPER FORMED FOLLOWER. A worn or improperly formed follower may cock or bind in its slideways in the receiver and thus prevent it from forcing the cartridge upward to its proper position in front of the bolt. Remove the follower and slide assembly and check angle of the follower as outlined in paragraph 21a. Replace a badly worn follower.

45. Bolt Fails To Release When Clip Is Latched.

This condition may be due to the following causes:

a. INSUFFICIENT RADII OR BURRS ON CATCH AND OPERATING ROD HOOKS. Insufficient radii or burrs on the hooks of the operating rod and operating rod catch may prevent them from "riding over" each other, thus preventing the bolt from releasing when the clip is inserted and latched. This condition may be remedied by lightly stoning the edges of the hooks with a fine-grained sharpening stone. Extreme care must be exercised when stoning so that the radii are not enlarged excessively as this will cause the bolt to release before the clip is latched. (See par. 46 below).

b. BULLET GUIDE LOW AT ACCELERATOR BEARING POINT. If the bullet guide is worn sufficiently at the accelerator bearing point (fig. 30), the follower arm acting upon the accelerator will fail to cam up the operating rod catch sufficiently for it to clear the operating rod hook and the bolt will not go forward when the clip has been inserted and latched. Replace bullet guide to correct this condition.

46. Bolt Releases Before Clip Is Latched.

The reverse of the causes of the bolt failing to release when the clips is inserted, listed in paragraph 45, above, may cause this condition. In addition it may be due to a defective clip latch or clip latch spring. If the radii on the hooks of the operating rod or operating rod catch are excessive and causing the bolt to go forward before the clip is latched, replace the parts. A bullet guide that is high at the accelerator bearing point should be removed from the rifle and stoned at this point until the accelerator will not cam up the operating catch sufficiently to release the operating rod until the clip is fully inserted and latched. Hand function the clip latch to see if this is not binding in the receiver and that the clip latch spring has sufficient tension to rotate the clip latch on its hinge pin. If there is binding, examine for burrs and remove by stoning or filing. If binding is due to deformation or improper dimensions, replace the clip latch. Replace a weak or broken spring.

47. Bolt Fails To Stay In Rearmost Position After Firing The Last Round. Clip Held Inside Of Gun, Jammed On The Way Out By The Bolt.

This condition may be caused by insufficient power to drive the mechanism rearward far enough for the operating rod to engage the catch (par. 42, above), a binding clip latch (par. 46,above), or the following: With the bolt fully retracted and latched and the follower at its uppermost position, examine the clip locking lug at the rear end of the clip latch to see if it clears the receiver. If it does not clear the receiver, the arm of the operating rod catch is either broken off or deformed to the extent that it does not rotate the clip latch sufficiently for the locking lug to clear the receiver and release the clip. Replace a broken or deformed operating rod catch.

48. Failure To Eject Cartridge Case.

This may be caused by a short recoil (par. 42, above) or one of the following reasons:

a. WEAK OR MISSING EJECTOR SPRING. Remove the ejectore spring from the bolt as described in paragraph 19e and replace.

b. EJECTOR BINDING. Remove the cartridge ejector from the bolt as described in paragraph 19e. Examine for burrs on ejector. Also check for burrs and foreign matter in ejector aperture in bolt.

49. Failure To Eject Cartridge Clip.

This condition may be due to one or more of the following causes:

a. CLIP EJECTOR WEAK OR BROKEN. Remove the clip ejector from the trigger housing group in accordance with FM 23-5 and replace.

b. DISTORTED CLIP.

c. DEFORMED OR BROKEN OPERATING ROD CATCH. Refer to paragraph 47, above.

50. Failure Of Bolt To Open After Fire.

This is probably due to one of the following reasons:

a. PLUGGED GAS PORT. A plugged gas port in either or both the barrel and gas cylinder will prevent the expanding gas from passing through these ports to drive the operating rod and bolt to the rear. Refer to paragraph 21c and f for corrective action.

b. LOOSE GAS CYLINDER. If the gas cylinder is sufficiently loose on the barrel of the rifle, enough of the expanding gas will escape around the barrel so that the gas acting on the piston through the gas ports will be insufficient to drive the operating rod and bolt to the rear. Check the diameter of the barrel at the gas port. (See par. 21f). If the barrel is undersize, replace. If the barrel is of correct size, replace the gas cylinder.

c. GAS CYLINDER LOCK SCREW VALVE OPEN. Refer to paragraph 20g.

51. Failure To Fire.

The possible causes of failure to fire listed below are in addition to those listed in FM 23-5:

a. WEAK OR BROKEN HAMMER SPRING. A weak or broken hammer spring may fail to drive the hammer forward against the firing pin with sufficient force to fire the cartridge. This is indicated by a light indent in the primer. Remove the spring from the trigger housing group as outlined in FM 23-5, and replace.

b. LOWER TANG ON HAMMER STRIKES STUD ON TRIGGER GUARD. The rear tang on the hammer striking the stud on the trigger housing will cushion the blow of the hammer against the firing pin or possibly even prevent it from going forward far enough to strike the firing pin. Remove the trigger housing group from the rifle, cock and release the hammer. Note if the rear tang on the hammer is striking the stud on the trigger housing. If the hammer does strike the stud, disassemble the trigger housing group as outlined in FM 23-5, and grind the tang on the hammer sufficiently to clear the stud when the hammer is in its forward position.

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