This set of instructions are for those that want/need to field strip their AR-15 either for cleaning purposes or to inspect the rifle. There is also a video attached to the last step, in case you want to use that instead or use it as a supplement.
DANGER: AR-15 are not toys, exercise the fundamental rules whenever handling a firearm. Always keep it pointed in a safe direction.
Step 1: Required Items
1. AR-15 Rifle
2. Work Area
3. Small Tool with Narrow End (Small Hex Key) (Optional)
Step 2: Clearing and Safety Checking the Rifle
Clearing the Rifle:
Point the rifle in a safe direction, remove the magazine, and pull the charging handle all the way back a few times to ensure the chamber is empty
Safety Checking the Rifle:
Pull the bolt back all the way with the charging handle and hold it while looking into the action to visually check that there are, indeed, no rounds currently in the chamber.
Step 3: Remove the Rear Take-down Pin
There are 2 pins holding the upper and lower receiver together, the one that is toward the rear (The end with the butt stock) of the rifle is the one that will be removed and is called the rear take-down pin
Make sure the bolt is in the forward position and remove the rear take-down pin by pushing the small end in with your finger, then pull the other, bigger, end out. The pin should not come all the way out (It should be retained in the lower receiver), but should be pulled out enough to separate the lower and upper receiver and should be hinged by the forward take-down pin, which is the second pin that is towards the front (The end opposite of the butt stock) of the rifle.
Step 4: Remove Charging Handle and Bolt Carrier Group
Slowly separate the upper and lower receiver, in case any parts came loose and may fly out. At this point, you have a choice, you can either pull out the forward take-down pin and completely separate the upper and lower receiver or you can just leave it in and pivot it open. For the sake of this set of instructions, we will leave the forward take-down pin in, but it will make no difference either way in regards to the actual field stripping of the rifle.
Next, slowly pull the charging handle back, while the upper and lower receivers are separated, about half-way. Then pull the bolt carrier group out and set it aside. Lastly, remove the charging handle, but be careful of the notches that are on the charging handle. You will have to lift the charging handle away from the top of the rifle to ensure that the notches don't catch on the upper receiver. Once taken out, set that aside also.
Step 5: Disassemble Bolt Carrier Group
Now for the most complex part of field stripping an AR-15, disassembling the bolt carrier group(BCG). First, remove the retaining pin. The retaining pin is the pin that has a little loop in it that you can grab with your fingernail, it keeps the firing pin from falling out. The retaining pin is located near the rear(the open end of the BCG) of the BCG inside of a little indent in the bolt carrier. If you are unable the pull the pin out with your finger nail, you can use an object with a small tip to pull it out, such as a small hex key.
After removing the retaining pin, just tip the BCG backwards and the firing pin should slide out, but in some cases, there may be too much carbon build up on the firing pin and it may not slide out, in which case you can pull it out with your finger or pry it out with the same object you used to pull out the retaining pin.
Once the firing pin is removed, you can now remove the cam pin. The cam pin is the large pin that is in a slot that is near the front(closed end of the BCG) of the BCG. To remove it, push the bolt in towards the rear of the BCG, then rotate the cam pin so that the straight edges of the pin are parallel with the bolt carrier, then pull it out, it may take some rotating and wiggling.
The last step is removing the bolt. The bolt is the part that closes off the front of the BCG. To remove it, pull it out, it may be hard to pull out, if not lubed correctly or due to carbon build up.
You are now done field stripping the upper receiver.
Step 6: Remove Buffer Spring and Buffer
The last step to field stripping an AR-15, is removing the buffer spring and buffer from the lower receiver. The buffer spring and buffer are housed inside of the buffer tube, which is covered by the butt stock. If you look at the open end of the buffer tube, you will see the buffer detent sticking up, holding the buffer spring and buffer inside of the buffer tube. Depress the buffer detent slowly till the buffer comes out, be careful, the buffer spring, buffer, and buffer detent can shoot out if you are not paying attention.
Step 7: Reassemble
Now that you have successfully field stripped the AR-15, you need to reassemble it. To reassemble it, you do everything you did in reverse, but there are a few things to pay particular attention to:
When reassembling the BCG, make sure the bolt face is rotated so that the extractor is in the 10 O'clock position.
When reassembling the BCG, when you put the cam pin back in, make sure you rotate it so that the straight edges are perpendicular to the BCG, otherwise the firing pin won't go in all the way.
When putting the charging handle into the rifle, make sure that the notches in the charging handle go into the cut-outs in the upper receiver, otherwise the charging handle won't go in.
When putting the BCG back into the upper receiver, make sure the bolt is pulled out, otherwise the BCG will not fit into the upper receiver.
Step 8: Function Check and Safety Check
After the rifle has been reassembled, all that is left to do is to function check and safety check the rifle.
The function check the rifle, pull the charging handle all the way back and release it. It should be able to be pulled back and released smoothly, if it catches or doesn't run smoothly, you may need to lubricate some of the parts.
The final step is to safety check the rifle once again, this may seem redundant and pointless, but safety is key and it doesn't take long. To safety check the rifle, pull the charging handle back and visually look into the chamber to ensure it is clear.
You have now completely field stripped an AR-15 and reassembled it.
There is a video attached to this step on how to do most of what I have mentioned in this set of instructions, the only thing that it does not include is the removal of the buffer and buffer spring. If you need further assistance on how to field strip a rifle, you can look up more videos on YouTube.