The following discussion on maintenance of the M870 shotgun covers only action necessary for routine maintenance of the weapon. Maintenance is performed according to the MRCs for this weapon.
Before any disassembly of the M870 shotgun is attempted, be sure no shells remain in the chamber or magazine.
BARREL.- To remove and clean the barrel, push the safety to the SAFE position. Open the action, unscrew the magazine cap, and pull the barrel from the
receiver. Replace the magazine cap on the end of the magazine tube. To clean the barrel, use a cleaning rod with a lightly oiled cloth. If powder fouling remains in the barrel, use a powder solvent to scrub the bore. After using solvent, wipe the barrel clean and re-oil it very lightly. Replace the barrel by removing the magazine cap, insert the barrel in the receiver, and replace the magazine cap.
TRIGGER PLATE ASSEMBLY.- Wlth the safety pushed to the SAFE position, cock the action. Tap out the front and rear trigger plate pins (fig. 3-54A). Lift the rear of the trigger plate from the receiver, then slide it rearward to remove it from the gun. The trigger assembly will be cleaned as a unit by brushing with a solvent. Wipe the trigger assembly dry and re-oil it very sparingly. When replacing the plate assembly in the gun, make sure the action bar lock enters the receiver easily and operates in position.
FORE-END ASSEMBLY UNIT.- Push the safety to the SAFE position. Close the action and
remove the magazine cap and barrel. Reach into the bottom of the receiver and press the left shell latch inward. Remove the fore-end by sliding it forward off the magazine tube. After the fore-end assembly has been removed from the gun, the breech bolt parts and the slide may be lifted from the ends of the action bars.
The top right edge of the slide may bind on the bottom front edge of the ejector port in the receiver. To free the slide, push downward on the front end of the bolt.
It is not necessary to disassemble the bolt for routine cleaning. Brush it with solvent to clean, then wipe it dry.
Assembly of the weapon is done in reverse of disassembly. There are, however, set procedures to follow to facilitate the assembly.
When you are assembling the fore-end parts, the gun must be cocked. During this assembly, place the slide in the correct position on the ends of the double-action bar. Place the breech bolt assembly, which includes the attached locking block assembly, over the slide on the action bars. Insert the end of the action bars into the matching grooves in the receiver. Move the fore-end slowly until contact is made with the front end of the right shell latch. Press the front right shell latch into the side of the receiver and continue moving the fore-end past this latch until contact is made with the left shell latch. Press the front of the left shell latch in to allow the fore-end assembly to pass and move freely into the receiver. Assemble the barrel to the receiver and tighten it firmly with the magazine cap. This completes the assembly of the shotgun.
For further information on the Remington M870 shotgun, refer to the U.S. Air Force TM TO-11W3-6-2-1.
MOSSBERG M500 SHOTGUN
While very similar to the M870, the Mossberg M500 has a few significant differences. The following is a brief description of the differences that affect operation of the weapon. Figure 3-55 shows the location of the safety switch and the action lock lever on the M500 shotgun. The M500 safety switch is located on the top of the receiver and the action lock release is to the rear of the trigger guard. The M870 has the safety switch in the trigger guard and the action lock release to the front of the trigger guard. The disassembly and maintenance of the M500 is basically the same as that of the M870 so much so that they are both currently covered on the same MRC. Further information on the Mossberg M500 shotgun maybe found in the manual
supplied with the weapon.
Figure 3-55.-Mossberg M500 shotgun safety and action release.