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Malfunctions, Probable Causes, Corrective Actions

Malfunctions are caused by
procedural or mechanical failures of the rifle,
magazine, or ammunition. Pre-firing checks and
serviceability inspections identify potential problems
before they become malfunctions. This paragraph
describes the primary categories of malfunctions.

  1. Failure to Feed, Chamber, or Lock. A
    malfunction can occur when loading the rifle or during
    the cycle of operation. Once the magazine has been
    loaded into the rifle, the forward movement of the
    bolt carrier group could lack enough force (generated
    by the expansion of the action spring) to feed,
    chamber, or lock the bolt


    Failure to Feed, Chamber or lock

               (Click image to
    view larger image)

    1. Probable Causes. The cause could be the
      result of one or more of the following:

      • Excess accumulation of dirt or fouling in and
        around the bolt and bolt carrier.
      • Defective magazine (dented, bulged, or a weak
        magazine spring).
      • Improperly loaded magazine.
      • Defective round (projectile forced back into
        the cartridge case, which could result in a
        stubbed round or the base of the previous
        cartridge could be separated, leaving the
        remainder in the chamber).
      • Damaged or broken action spring.
      • Exterior accumulation of dirt in the lower
        receiver extension.
      • Fouled gas tube resulting in short recoil.
      • A magazine resting on the ground or pushed
        forward could cause an improper lock.
    2. Corrective Action. Applying immediate
      action usually corrects the malfunction. To avoid
      the risk of further jamming, the firer should watch
      for ejection of a cartridge and ensure that the
      upper receiver is free of any loose rounds. If
      immediate action fails to clear the malfunction,
      remedial action must be taken. The carrier should
      not be forced. If resistance is encountered, which
      can occur with an unserviceable round, the bolt
      should be locked to the rear, the magazine removed,
      and the malfunction cleared. For example, a bolt
      override is when a cartridge has wedged itself
      between the bolt and charging handle. The best way
      to correct this problem is by

      • Ensuring the charging handle is pushed forward
        and locked in place.
      • Securing the rifle and pulling the bolt to the
        rear until the bolt seats completely into the
        buffer well.
      • Turning the rifle upright and allowing the
        overridden cartridge to fall out.
  2. Failure to Fire Cartridge. This is a
    failure of a cartridge to fire despite the fact that a
    round has been chambered, the trigger pulled, and the
    sear released the hammer. This occurs when the firing
    pin fails to strike the primer with enough force or
    when the ammunition is defective.

    1. Probable Causes. Excessive carbon buildup
      on the firing pin (Figure 3-2, A) is often the
      cause, because the full forward travel of the firing
      pin is restricted. A defective or worn firing pin
      can give the same results. Inspection of the
      ammunition could reveal a shallow indentation or no
      mark on the primer, indicating a firing pin
      malfunction (Figure 3-2, B). Cartridges that show a
      normal indentation on the primer, but did not fire
      indicate faulty ammunition.

      Failure to fire

                 (Click image to
      view larger image)
    2. Corrective Action. If the malfunction
      continues, the firing pin, bolt, carrier, and
      locking lug recesses of the barrel extension should
      be inspected, and any accumulation of excessive
      carbon or fouling should be removed. The firing pin
      should also be inspected for damage. Cartridges that
      show a normal indentation on the primer, but failed
      to fire could
      indicate a bad
      ammunition lot. Those that show a complete
      penetration of the primer by the firing pin could
      also indicate failure of the cartridge to fully seat
      in the chamber.

      NOTE: If the round is
      suspected to be faulty, it is reported and returned
      to the agency responsible for issuing ammunition.

      WARNING If an audible “POP”
      or reduced recoil occurs during firing, immediately
      cease-fire. This POP or reduced recoil could be the
      result of a round being fired without enough force
      to send the projectile out of the barrel. Do not
      apply immediate action. Remove the magazine, lock
      the bolt to the rear, and place the selector lever
      in the safe position. Visually inspect the bore to
      ensure a projectile is not lodged in the barrel. If
      a projectile is lodged in the barrel, do not try to
      remove it. Turn the rifle in to the armorer.


  3. Failure to Extract. A failure to extract
    results when the cartridge case remains in the chamber
    of the rifle. While the bolt and bolt carrier could
    move rearward only a short distance, more commonly the
    bolt and bolt carrier recoil fully to the rear,
    leaving the cartridge case in the chamber. A live
    round is then forced into the base of the cartridge
    case as the bolt returns in the next feed cycle. This
    malfunction is one of the hardest to clear.

    WARNING A failure to extract
    is considered an extremely serious malfunction,
    requiring the use of tools to clear. A live round
    could be left in the chamber and accidentally
    discharged. If a second live round is fed into the
    primer of the chambered live round, the rifle could
    explode and cause personal injury. This malfunction
    must be properly identified and reported. Failures to
    eject should not be reported as extraction failures.


    1. Probable Cause. Short recoil cycles and
      fouled or corroded rifle chambers are the most
      common causes of failures to extract. A damaged
      extractor or a weak or broken extractor spring can
      also cause this malfunction.
    2. Corrective Action. The severity of a failure to
      extract determines the corrective action procedures.
      If the bolt has moved rearward far enough to strip a
      live round from the
      magazine in
      its forward motion, the bolt and carrier must be
      locked to the rear. The magazine and all loose
      rounds must be removed before clearing the stoppage.
      Usually, tapping the butt of the rifle on a hard
      surface causes the cartridge to fall out of the
      chamber. However, if the cartridge case is ruptured,
      it can be seized. When this occurs, a cleaning rod
      can be inserted into the bore from the muzzle end.
      The cartridge case can be forced from the chamber by
      tapping the cleaning rod against the inside base of
      the fired cartridge. If cleaning and inspecting the
      mechanism and chamber reveals no defects but
      failures to extract persist, the extractor and
      extractor spring should be replaced. If the chamber
      surface is damaged, the entire barrel must be
  4. Failure to Eject. Ejection of a cartridge
    is an element in the cycle of functioning of the
    rifle, regardless of the mode of fire. A malfunction
    occurs when the cartridge is not ejected through the
    ejection port and either remains partly in the chamber
    or becomes jammed in the upper receiver as the bolt
    closes. When the firer initially clears the rifle, the
    cartridge could strike an inside surface of the
    receiver and bounce back into the path of the bolt.

    1. Probable Cause. The cartridge must
      extract before it can eject. Failures to eject can
      also be caused by a buildup of carbon or fouling on
      the ejector spring or extractor, or from short
      recoil. Short recoil is usually due to a buildup of
      fouling in the carrier mechanism or gas tube, which
      could result in many failures to include a failure
      to eject. Resistance caused by a carbon-coated or
      corroded chamber can impede the extraction, and then
      the ejection of a cartridge.
    2. Corrective Action. While retraction of
      the charging handle usually frees the cartridge and
      permits removal, the charging handle must not be
      released until the position of the next live round
      is determined. If another live round has been
      sufficiently stripped from the magazine or remains
      in the chamber, then the magazine and all live
      rounds could also require removal before the
      charging handle can be released. If several
      malfunctions occur and are not corrected by cleaning
      and lubricating, the ejector spring, extractor
      spring, and extractor should be replaced.
  5. Other Malfunctions.
    The following
    paragraphs describe some other malfunctions that can

    1. The bolt fails to remain in a rearward position
      after the last round in the magazine is fired. Check
      for a bad magazine or short recoil.
    2. The bolt fails to lock in the rearward position
      when the bolt catch has been engaged. Check bolt
      catch; turn in to unit armorer.
    3. The weapon fires two or more rounds when the
      trigger is pulled and the selection lever is in the
      SEMI position. This indicates a worn sear, cam, or
      disconnector. Turn in to armorer to repair and
      replace trigger group parts as required.
    4. The trigger fails to pull or return after
      release with the selector set in a firing position.
      This indicates that the trigger pin has backed out
      of the receiver or the hammer spring is broken. Turn
      in to armorer to replace or repair.
    5. The magazine fails to lock into the magazine
      well. Check the magazine and magazine catch for
      damage. Turn in to armorer to adjust the catch;
      replace as required.
    6. Any part of the bolt carrier group fails to
      function. Check for incorrect assembly of
      components. Correctly clean and assemble the bolt
      carrier group, or replace damaged parts.
    7. The ammunition fails to feed from the magazine.
      Check for damaged magazine. A damaged magazine could
      cause repeated feeding failures and should be turned
      in to the armorer or exchanged.

NOTE: Additional technical information on
troubleshooting malfunctions and replacing components is
contained in the organizational and direct support
maintenance publications and manuals

Other Possible Malfunctions

(Click image to view larger image)

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