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Inspection, Cleaning, and Lubrication

  • After firing, clean your rifle as soon as possible to make the job easier and to avoid allowing the development of any corrosion.
  • When your firearm has not been fired, you should clean it at least once or twice a year if you live in a temperate climate, or as often as once a week in a tropical climate.
  • If you get your firearm wet, clean it as soon as possible.


Use a high quality rifle cleaning kit that includes a cleaning rod; swab holder; cotton flannel bore patches; pipe cleaners; a small toothbrush; brass wire bristle bore and chamber brushes and a Cleaner/Lubricant/Preservative (CLP in Army terminology).

After you have disassembled the rifle, thoroughly clean, inspect and lubricate all parts according to the techniques described on following pages.

Detailed cleaning techniques…

NOTE: The procedures below describe cleaning with a standard multi-piece rod cleaning kit. Other commercial cleaning kits may include alternate cleaning instructions which may be just as effective.


CLEANING THE BORE: The bore of your Bushmaster rifle has lands and grooves called rifling. Rifling makes the bullet spin very fast as it moves down the bore and down range. It is difficult to push a new, stiff bore brush through the bore. You will find it much easier, and more effective, to pull your bore brush through the bore. Also, because the brush will clean better if the bristles follow the grooves (this is called tracking), you want the bore brush to be able to turn as you pull it through. Always clean from from chamber toward the muzzle. This is how it’s done:

  1. Swab out the bore with a patch moistened with “CLP”.
  2. Attach three rod sections together but leave each one about two turns short of being tight.
  3. Attach the bore brush but leave it two turns short also.
  4. Point muzzle down. Hold the upper receiver in one hand while inserting the end of the rod without the brush into the chamber. Guide the rod carefully through the bore. CAUTION: do not let the rod or its threaded end scratch the Bore or Firing Chamber. About 2 - 3 inches of the rod should protrude out of the muzzle.
  5. Attach the handle section of the cleaning rod to the end of the rod sticking out of the muzzle.
  6. Pull the brush through the bore and out the muzzle. You should be able to see the rod twisting as you pull it - this is the brush “tracking” in the rifling.
  7. After one pull, take off the handle section and repeat the process. After three or four pulls, the three rod sections and the bore brush may become screwed tightly together. Loosen them up and repeat the process.
  8. Send a patch through the bore occasionally to clean out any debris that the brush is getting loose. Just replace the bore brush with the rod tip (patch holder) and a wet patch. Pull it through. If you leave the rods loose, the patch will also “track” in the rifling. Always have the bore wet with cleaner before pulling a brush through.

Cleaning the upper receiver…

NOTE: Check to ensure that there is no looseness between the barrel and the upper receiver - if you detect any movement by twisting with your hands, the barrel nut must be re-torqued. Bring the rifle to a qualified gunsmith.


  1. Using a “CLP“ product, clean all areas of powder, corrosion, dirt and rust. Never use a wire brush or any type of abrasive to clean the aluminum upper receiver - you'll scratch and damage the finish.
  2. Clean the firing chamber - dip the chamber cleaning brush in CLP and use at least five plunge strokes and three 360 clockwise rotations. Then swab out the bore as described previously to remove any contaminated solution or loosened debris.
  3. Use the bore cleaning brush, still wet with CLP, and clean carbon and powder residue from around the gas tube, run a pipe cleaner into the gas tube, clean the bolt locking lugs, bolt rings, firing pin, bolt cam pin, lip of the extractor, and inside the bolt carrier from both front and rear.
  4. Wipe all components clean and dry, and inspect for excessive wear, corrosion or mechanical damage. Replace any defective parts before firing (order new parts at 1-800-998-7928).


Cleaning the lower receiver…

  1. Clean all areas of powder fouling, corrosion, dirt and rust. Again, never use a wire brush or any type of abrasive to clean the aluminum lower receiver.
  2. Wipe any dirt from the trigger mechanism. Clean the buffer, action spring, and inside the lower receiver extension (the buffer tube).



Cleaning the ejector…

The design of the ejector makes its disassembly for cleaning somewhat impractical (i.e. we don't recommend it). Make sure your Bushmaster ejects empty cases efficiently by following these steps on a monthly basis (more frequently if firing blanks).

  1. Remove the bolt from the carrier (as described previously). Hold it as shown with the ejector down and the extractor up.
  2. Dribble a few drops of CLP around the ejector to form a puddle.
  3. Take a fired or dummy case and place it under the lip of the extractor. With a rocking motion, press the case down against the ejector. Since the ejector is spring loaded, some resistance will be felt. Press on the case until it stops against the bolt face. Ease off with your thumb slightly and press down again. Repeat several times. Replace the CLP frequently. Once the spring action of the ejector is smooth and strong, dry off any excess.

Inspection before lubricating…

  1. Check the bolt: Look for cracks or fractures, especially in the cam pin hole area. Bolts with any pitting extending into the firing pin hole should be replaced.
  2. Check the firing pin; if it is bent, cracked, too bunted or too sharp, it should be replaced.
    WARNING: If cam pin is missing, DO NOT FIRE THE RIFLE! It will explode!
  3. Check the firing pin retaining pin: If it is bent, or badly worn, it should be replaced. Never use a “cotter pin” as a substitute for a real firing pin retaining pin. Cotter pins are not made of heat treated spring steel and their round head shape will cause damage.
  4. Check the cam pin: If it is cracked, or chipped, it should be replaced.
  5. Check the extractor and extractor spring: If the extractor is chipped, or has broken edges in the area of the lip that engages the cartridge rim, it should be replaced.

Lubrication – upper receiver…

Lightly lubricate:

  • The inside of the upper receiver, the bore and chamber (using the cleaning rod and a patch), the outer surfaces of barrel, front sight, and surfaces under the handguard.
  • Be sure you lube in and around all the locking lugs (see illustration below). Depress the front sight detent and apply 2-3 drops of CLP to it. Depress the detent several times to work the lubricant into the spring.
  • The firing pin and the firing pin recess in the bolt with CLP.
  • The charging handle, the inner and outer surfaces of the bolt carrier, the extractor and its pin. The inside of the carrier key should be dried with a pipe cleaner – then place one drop of CLP inside.

Generously lubricate:

  • The slide and cam pin area of the bolt carrier, the bolt, and the bolt gas rings.

Lubrication – lower receiver…

Lightly lubricate:

  • Inside the lower receiver extension (buffer tube), buffer and the action spring.

Generously lubricate:

  • All moving lower receiver parts trigger, hammer, safety, bolt catch, forward assist, etc), and their various pins and detents. Don't forget the takedown and pivot pins and detents. Clean fingerprints (they can start the corrosion process) off the exterior surfaces with a oiled black rag (black rags leave no visible lint).

Lubrication – bolt carrier group…

  • Lightly lubricate the firing pin with CLP - also the firing pin recess in the bolt.
  • Generously lubricate the bolt, its cam pin area, the bolt gas rings. A lighter application is good on the extractor and its pin.
  • Lightly lubricate the charging handle and the inner and outer surfaces of the bolt carrier.
  • Generously lubricate the slide and cam pin area of the bolt carrier.
  • The inside of the carrier key on the bolt carrier should be dried with a pipe cleaner or cotton swap - then place one drop of CLP inside.

Lubrication – adjustable rear sight…

Note: Record how far you move the rear sight so it can be returned to its original position upon the completion of this task.

Rear Sight Moving Parts:

Use 1 or 2 drops of CLP. Rotate these parts to ensure that the lubricant is spread evenly above, below and around the threads of the:

  • Elevation knob
  • Elevation screw shaft
  • Windage knob
  • Windage screw
  • Detent holes


Elevation Screw Shaft:

Also lube from inside the upper receiver as follows:

  • Turn upper receiver upside down
  • Remove charging handle
  • Put 2 or 3 drops on bottom of elevation screw shaft and in elevation detent spring hole
  • Rotate the elevation dial back and forth a few times while keeping upper receiver upside down


  1. Insert action spring and buffer. Depress buffer detent and push buffer in past the detent, then release.
  2. Insert extractor, plunger, and spring.
  3. Push in extractor pin.
    STAGGER THE GAS RING GAPS TO REDUCE GAS LOSS. Position the three ring gaps 120 apart around the bolt.
  4. Slide bolt into carrier.

WARNING: If cam pin is missing, DO NOT FIRE THE RIFLE! It will explode!

NOTE: The bolt is machined so as to allow insertion of the cam pin from one side only. This provision aligns the extractor and ejector properly within the upper receiver.

  1. Replace bolt cam pin.
  2. Drop in and seat the firing pin.
  3. Pull bolt out.
    NOTE: Firing pin should not fall out when bolt carrier group is turned upside down.
  4. Replace firing pin retaining pin
  5. Engage, then push charging handle part way
  6. Position carrier key in slotted bottom of charging handle. Slide in bolt carrier group.
    CAUTION: Bushmaster does not recommend the practice of swapping bolts between different rifles. doing so could result in damage, personal injury, or death.
  7. Push charging handle and bolt carrier group into receiver together.
  8. Join Upper and Lower Receivers.
  9. Engage Receiver Pivot Pin.
    CAUTION: Selector lever should be on SAFE before closing Upper Receiver.
  10. Close the upper and lower receiver groups and push in the takedown pin.
    When removing or reattaching the handguards, use a hanguard removal tool (part #HGD-Tool) or use the “Buddy System” as describe below.
  11. Place the rifle on the buttstock and press down on the slip ring with both hands. Note: The “Half-Round” Handguards are identical and can be used on top or bottom.
  12. Have your buddy install one handguard on top and the other on the bottom.
  13. Reattach the sling.

Safety function check…


  1. Remove magazine if installed. Pull charging handle assembly to rear. Check that the chamber is clear. Let bolt and bolt carrier close. DO NOT PULL TRIGGER. Leave hammer in cocked position.
    WARNING: If rifle fails any of the following tests, continued use of the Rifle could result in injury to, or death of, personnel.
  2. Place Selector Lever in SAFE position and pull trigger. The hammer should not fall.
  3. Place Selector Lever in FIRE position. Pull trigger. The hammer should fall.
    NOTE: For the purpose of the following check, “SLOW” is defined as one fourth to one half the normal rate of trigger release.
  4. Hold trigger to the rear, pull charging handle to the rear and release charging handle. Let off pressure on the trigger with a slow, smooth motion, without hesitations or stops, until the trigger is fully forward. An audible click should be heard – the hammer should not fall.
  5. Repeat the FIRE position test five times. The rifle must not malfunction during any of these five tests. If the rifle malfunctions during any of these five tests, have the rifle checked by a qualified gunsmith.

Loading a magazine…

  • Use only quality ammunition suitable for your firearm. Examine each cartridge – particularly around the primer.
  • Look for dents, scratches, and other signs of damage. Do not load damaged ammunition.
  • With the magazine facing forward as shown in the illustration, place a round between the lips of the magazine with the bullet tip forward. Push the round down until it is held by the magazine lips.
  • If necessary, give the round a slight push backward to seat it against the back edge of the magazine lips. Place next round on top of previous round and repeat steps until desired number of rounds are loaded.

The forward assist...

CAUTION: Safe firearms handling dictates that you load live ammunition into your rifle only when you are ready to shoot.

The forward assist helps lock the bolt into the barrel, but it will only be useful on rare occasions when the bolt fails to lock automatically. If you find that you need to use the forward assist it is probably time you cleaned your rifle – pay particular attention to the locking lug areas in the chamber and on the bolt.

CAUTION: Before using the forward assist, make sure your ammunition is clean and undamaged. Forcing dirty or damaged ammunition into the chamber could damage your rifle and could result in injury, death or property damage.

Adjustable front sight post…

The front sight post is threaded - allowing it to be moved up or down when “Zeroing” the rear sight (see “Zeroing Your Sights”)


A2 dual aperture rear sight…


NORMAL RANGE - The smaller aperture is unmarked and is used for most firing situations. It is used in conjunction with the elevation knob for 300, 400, 500, 600, 700, 800, and 1000 meter targets.

Zeroing your sights…

This is the procedure to follow in order to “Zero” your mechanical sights.

  1. In this procedure, the front sight post and rear sight windage knob are adjusted so that you can hit your point of aim at 300 meters:
  2. Flip the unmarked (smaller) aperture to the up position (as shown).
  3. Set the rear sight so that the 300-meter mark is aligned with the mark on the left side of the receiver.

Zeroing adjustments…

  1. During zeroing procedures, only the front sight post and windage knob are adjusted to move the strike of the bullet on the target.
  2. Also see the detailed zeroing procedures below.


FRONT SIGHT: To adjust elevation, depress detent and rotate post. To raise strike of bullet, rotate post in the direction of arrow marked UP. Reverse the direction of rotation to lower strike of bullet. Each graduation (notch) moves the point of impact of bullet as indicated.

Impact Distance
0.9 cm (3/8 in.) 25 meters
3.5 cm (1 3/8 in.) 100 meters
7.0 cm (2 3/4 in.) 200 meters

For windage knob (per click)*

Impact Distance
0.3 cm (1/8 in.)
1.25 cm (1/2 in.)
2.50 cm (1 in.)
3.8 cm (1 1/2 in.)
5.0 cm (2 in.)
6.3 cm (2 1/2 in.)
7.6 cm (3 in.)
8.8 cm (3 1/2 in.)
10.0 cm (4 in.)

*AII of the above values have been rounded off.

Note: To remember your correct zero windage, note location of windage scale and windage knob pointer (heavy mark on outside of knob). Once you have established your correct zero windage leave your windage Scale and windage knob pointer on these settings at all times.

25 meter zeroing procedures…

Place an appropriate 25 meter paper sighting target 25 meters down range and follow the steps below to establish a “battlesight” zero.

  1. Do not move the front sight post on your rifle at this time. It was set at the factory and should be very close to zero.
  2. Center the rear sight aperture by turning the windage knob left or right. This is called “Mechanical Zero Windage”.
  3. The unmarked (smaller) aperture should be up.
  4. Now rotate the elevation knob “up” one click past the 300 - meter mark. From this point on, the elevation knob should not be moved. Any changes in elevation required in the following zeroing steps are made to the front sight post only.
  5. Carefully aim and fire at the center of the target bull’s-eye.
  6. If your shot group is not in the center of the bull’s-eye, use the squares on the target sheet to calculate the required “clicks” necessary to move your next shot group into the bull’s-eye.
    Remember - any changes in elevation are made by moving front sight post only!
  7. In order to raise your next shot group, rotate the front sight post clockwise. To lower shot group, rotate front sight post counterclockwise.
    Changes in windage are made with the windage knob. In order to move the shot group to the left, turn the windage knob counterclockwise. In order to move the shot group to the right, turn the windage knob clockwise.
  8. Carefully aim and fire another group at the center of the target bull’s-eye.
  9. Repeat Steps 7 through 9, if required.
  10. If your group is on target, your sight is now “calibrated.” To place your actual 300 - meter zero on the rifle, you must rotate the elevation knob one click “down.” (The range scale’s 300-meter mark should now be aligned with the mark on the rifle’s receiver).

Operating your rifle…

WARNING: If a noticeable difference in sound or recoil is experienced, STOP FIRING. Either condition could indicate an incomplete powder burn and/or a bullet stuck in the bore (also see Troubleshooting). Retract the bolt slowly and remove the fired cartridge case. Clear the weapon and check for unburned powder grains in the receiver or bore, and for a bullet stuck in the bore. Clean out any unburned powder before resuming firing. If a bullet is stuck in the bore, do not attempt to remove it. Take the rifle to a qualified gunsmith.


CAUTION: Always point the muzzle in a safe direction!

  1. With hammer cocked, place selector lever on SAFE.
  2. Open bolt and check chamber. Make sure it is clear.

Inserting a magazine…

  1. Push magazine up into magazine well until magazine catch engages and holds the magazine.
  2. Tap upward on magazine bottom to make sure it’s seated correctly.


Chambering a round with bolt assembly open…

NOTE: The magazine may be inserted into the rifle with bolt assembly open or closed.

  1. Depress upper portion of bolt catch. Bolt should spring forward.
  2. TAP the forward assist to ensure bolt is fully forward and locked.

Chambering a round with bolt assembly closed…

  1. Pull charging handle fully to rear.
  2. Release the charging handle.
  3. TAP the forward assist to ensure bolt is fully forward and locked.

NEVER “Ride” the charging handle. Let it move forward on its own.

Note: If the rifle is not going to be fired immediately, make sure the selector lever is still on safe, and close the ejection port cover to keep out dirt.

Always keep muzzle pointed in safe direction.

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