How To: M4 Tear Down
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This article is written as a simple guide that can be followed to tear down your M4. Please remember that not all guns are constructed the same, and ASR and its staff can't be held responsible for anything you break.
The first step is to clear the rifle, remove the magazine, the battery, and turn the hop-up all the way down.
With the gun made safe, begin the disassembly by removing the sliding stock. To do this, pull down on the back side of the lever, and pull the stock rearward. If you have a fixed stock, open it and remove the bolts securing it to the gun.
With the stock removed, use the appropriate tool to remove the screw from the stock tube cover. It is typically an Allen or Phillips head screw. Once the screw is out, the cover will pull out.
With the tube cover removed, insert the proper screwdriver into the tube and remove the long bolt. The tube will now pull off of the gun.
With the stock done, move to the front of the rifle, and disconnect the wires running from the battery plug to those running into the gun.
Move to the grip of the gun, and remove the two screws holding the motor plate in place. These can be either slotted, Allen, or most commonly Phillips drive.
With the plate loose, you can remove it, and the motor height adjustment disc. The disc may fall into the grip. Don't worry it will get stuck to the motor.
With the plate removed you can disconnect the leads from the motor terminals. Be careful here, the leads on some guns are very fragile, and can snap.
Pull the motor out.
Now that the grip is hollow, insert the correct drive screwdriver, and remove the two screws holding the grip to the gearbox, be careful not to strip the screws.
With the grip released from the gearbox, pull it away, and gently pull the wires through the holes.
With the grip removed, push the pin out of the lower receiver. One end is checkered, so that the pin will only go out one way. In the example the pin pushes out from right to left.
Do not force the pin if it won't come out; instead try it from the other side. If you force it through you may damage the pin, and widen the holes in the body.
Remove the magazine catch next. Place one hand on the back side (left side) of the rifle to support the mag catch. Begin by removing the screw from the center of the mag release button; now remove the button and then the spring the latch will now fall out from the other side.
The last step before separating the upper and lower receivers is to remove the body pins. The pins are pushed in from the left side and secured on the right side with a screw. Remove the screws, and knock the pins through from right to left.
Now we can finally separate the receivers.
Push forward on the bottom of the gearbox, while pulling down and back on the stock tube. This action essentially rotates the lower receiver off of the gearbox, and is much easier said than done, thus I chose to add this video:
Now we can finally remove the gearbox. Depending on the way your rifle was built this may be as easy as pulling it directly to the rear of the gun, or it may involve pulling the charging handle back, and pulling the gearbox out simultaneously. Either way it's not too difficult. You can now take the gearbox apart, for which a guide is available here.
If need be, the hop-up can be removed by simply pushing it to the rear of the gun. If you need a guide for hop-up/barrel work, click here.
On reassembly, you will want to make sure you route the wires back to the front of the rifle correctly, this is pretty straight forward. Also, putting the lower receiver back on is the reverse of taking it off, again here is a video:
Well that does it. If you have any questions or need technical help, ask in the forums.